FINAL Lic MANUAL Studentcopy 1455085288190
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Transcript of FINAL Lic MANUAL Studentcopy 1455085288190
EC1015 LABORATORY POLICIES AND REPORT FORMAT
Reports are due at the beginning of the lab period. The reports are intended to be a complete documentation of the work done in preparation for and during the lab. The report should be complete so that someone else familiar with digital design could use it to verify your work. The prelab and post lab report format is as follows:
1. A neat thorough prelab must be presented to your Staff In charge at the beginning of your scheduled lab period. Lab reports should be submitted on A4 paper. Your report is a professional presentation of your work in the lab. Neatness, organization, and completeness will be rewarded. Points will be deducted for any part that is not clear.
2. In this laboratory students will work in teams of three. However, the lab reports will be written individually. Please use the following format for your lab reports.
a. Cover Page: Include your name, Subject Code, Section No., Experiment No. and Date.
b. Objectives: Enumerate 3 or 4 of the topics that you think the lab will teach you. DO NOT REPEAT the wording in the lab manual procedures. There should be one or two sentences per objective. Remember, you should write about what you will learn, not what you will do.
c.Design: This part contains all the steps required to arrive at your final circuit. This should include diagrams, tables, equations, K-maps, explanations, etc. Be sure to reproduce any tables you completed for the lab. This section should also include a clear written description of your design process. Simply including a circuit schematic is not sufficient.
e. Questions: Specific questions (Prelab and Postlab) asked in the lab should be answered here. Retype the questions presented in the lab and then formally answer them.
3. Your work must be original and prepared independently. However, if you need any guidance or have any questions or problems, please do not hesitate to approach your staff in charge during office hours. Copying any prelab/ postlab will result in a grade of 0. The incident will be formally reported to the University and the students should follow the dress code in the Lab session.
4. Each laboratory exercise (circuit) must be completed and demonstrated to your Staff In charge in order to receive working circuit credit. This is the procedure to follow:
a. Circuit works: If the circuit works during the lab period (3 hours), call your staff in charge, and he/she will sign and date it.. This is the end of this lab, and you will get a complete grade for this portion of the lab.
b. Circuit does not work: If the circuit does not work, you must make use of the
open times for the lab room to complete your circuit. When your circuit is ready, contact your staff in charge to set up a time when the two of you can meet to check your circuit.
5. Attendance at your regularly scheduled lab period is required. An unexpected absence will result in loss of credit for your lab. If for valid reason a student misses a lab, or makes a reasonable request in advance of the class meeting, it is permissible for the student to do the lab in a different section later in the week if approved by the staff incharge of both the sections. Habitually late students (i.e., students late more than 15 minutes more than once) will receive 10 point reductions in their grades for each occurrence following the first.
6. Final grade in this course will be based on laboratory assignments. All labs have an equal weight in the final grade. Grading will be based on pre-lab work, laboratory reports, post-lab and in-lab performance (i.e., completing lab, answering laboratory related questions, etc.,).The Staff In charge will ask pertinent questions to individual members of a team at random. Labs will be graded as per the following grading policy:
Internal Assessment Marks: 60 End Semester Examination Marks: 40Carrying out lab work & Report
: 25
Mini Project : 10Attendance : 05Model Exam : 20
Circuit diagram & Waveforms
: 10
Design / Calculation : 05Procedure : 05Tabulation / Graph : 10Result : 05Viva-Voce : 05
7. Reports Due Dates: Reports are due one week after completion of the corresponding lab.
8. Systems of Tests: Regular laboratory class work over the full semester will carry a weight age of 60%. The remaining 40% weightage will be given by conducting an end semester practical examination for every individual student if possible or by conducting a 1 to 1 ½ hours duration common written test for all students, based on all the experiment carried out in the semester.
9. General Procedure
a. Properly place the components in the general purpose breadboard and identify the positive and negative terminals of the power supply, before making connection.
b. Keep the required supply voltage in Power supply and connect power supply voltage and ground terminals to the respective node points in the breadboard.
c. Connect the components as per the circuit diagram, after verifying connection switch on the supply and note down the required parameter values
d. After completion of the experiments, switch off the power supply and return the components.
EQUIPMENT AND LABORATORY MAINTENANCE
Be responsible for equipment and laboratory maintenance. For example:
1. Keep the lab and benches neat and organized.
2. Use the equipment properly. For example, use only the probes that have been
compensated for your oscilloscope with your oscilloscope. An oscilloscope and its
matched probes are labeled by the same number to help you keep using them together.
Do not take the sleeve off the sensitive probe tip and use the probe tip directly (e.g.,
by inserting the probe tip directly into a hole on a breadboard). Many probes have
been permanently damaged when used this way because a) the fragile tip is broken by
the severe probing strain, b) the probe accidentally falls to the ground, breaking the
fragile tip, or c) the probe sleeve is lost after it is removed from the probe tip. A short
hook-up wire hooked to the probe will allow fine probing without using the probe tip
directly.
3. Return instruments, manuals, tools, components, cables, etc., to the proper storage
location.
4. Bring defective equipment to the lab staff or laboratory maintenance staff for repair.
5. Notify the lab staff when the stock is about to run out of a certain component.
USEFUL LABORATORY PRACTICES
In general, keep the following points in mind:
1. Identify lab objectives. An experiment should not be treated as a cookbook
procedure. Find a rationale behind each step.
2. Come to the lab prepared. Preview the experiment as homework.
3. Keep a lab notebook to record all activities during all lab sessions.
4. Finish as much as possible before leaving. This includes acquiring data, interpreting
data, answering questions, and revolving uncertainties.
5. All data are real. If data look unbelievable, check all the steps carefully. Consult the lab staff.
6. Safety is first. Change instrument settings slowly. Observe the effect of the most recent
change before proceeding with more change. Set voltage/current/power limit. It is important
that right from the beginning of your lab work you consider the possible interactions between
measuring instruments and the device under test. For example:
7. The input impedance of meters can cause measurement error in high impedance circuits.
8. The input capacitance of scopes, scope probes, or connecting cables may have important high
frequency loading effects.
9. When using an oscilloscope to make accurate waveform or frequency response measurements
with a x10 probe, make sure the probe is properly compensated.
10. Learn to use the current limiting features of the laboratory power supplies to protest the
device under test from possible damage under short circuit conditions.
11. Make sure to have low impedance ground connections between the test instruments and your
“breadboard”. Avoid groundloops!
The list could go on much longer. It represents the pitfalls of doing electronics in the real world.
IX. SAFETY PRECAUTIONS AND LABORATORY RULES
To be responsible for your own safety and keep the laboratory in a good order, you must comply with
the rules below.
Solid footwear must be worn by all students inside the laboratory. Staffs are required by the
university to ensure that everyone in the laboratory is wearing solid footwear. Students with
bare feet, thongs, sandals, or other forms of open footwear will not be allowed into the
laboratory.
No smoking, drinking, or eating is permitted in the laboratory (this includes chewing gum and
confectionaries).
Always have your circuits checked by a demonstrator before switching on, and always switch
the power off immediately after taking measurements.
Act sensibly and tidy up after yourself.
/There is a safety switch on each bench which switches power to (and protects) the GPO's
(general purpose outlets/power points).
Under no circumstances should you attempt to remove any of the panels on the bench. There
is a 220 volt supply behind them which could be lethal.
You should not take equipment from another bench. If something is faulty (or missing) ask
the lab staff for assistance.
SAFETY
Safety in the electrical laboratory, as everywhere else, is a matter of the knowledge of potential
hazards, following safety precautions, and common sense. Observing safety precautions is important
due to pronounced hazards in any electrical/computer engineering laboratory. Death is usually certain
when 0.1 ampere or more flows through the head or upper thorax and have been fatal to persons with
coronary conditions. The current depends on body resistance, the resistance between body and
ground, and the voltage source. If the skin is wet, the heart is weak, the body contact with ground is
large and direct, then 40 volts could be fatal. Therefore, never take a chance on "low" voltage. When
working in a laboratory, injuries such as burns, broken bones, sprains, or damage to eyes are possible
and precautions must be taken to avoid these as well as the much less common fatal electrical shock.
Make sure that you have handy emergency phone numbers to call for assistance if necessary. If any
safety questions arise, consult the lab demonstrator or technical assistant/technician for guidance and
instructions. Observing proper safety precautions is important when working in the laboratory to
prevent harm to yourself or others. The most common hazard is the electric shock which can be fatal
if one is not careful.
ELECTRIC SHOCK
Shock is caused by passing an electric current through the human body. The severity depends mainly
on the amount of current and is less function of the applied voltage. The threshold of electric shock is
about 1 mA which usually gives an unpleasant tingling. For currents above 10 mA, severe muscle
pain occurs and the victim can't let go of the conductor due to muscle spasm. Current between 100
mA and 200 mA (50 Hz AC) causes ventricular fibrillation of the heart and is most likely to be lethal.
What is the voltage required for a fatal current to flow? This depends on the skin resistance. Wet skin
can have a resistance as low as 150 Ohm and dry skin may have a resistance of 15 kOhm. Arms and
legs have a resistance of about 100 Ohm and the trunk 200 Ohm. This implies that 240 V can cause
about 500 mA to flow in the body if the skin is wet and thus be fatal. In addition skin resistance falls
quickly at the point of contact, so it is important to break the contact as quickly as possible to prevent
the current from rising to lethal levels.
EQUIPMENT GROUNDING
Grounding is very important. Improper grounding can be the source of errors, noise and a lot of
trouble. Here we will focus on equipment grounding as a protection against electrical shocks. Electric
instruments and appliances have equipments casings that are electrically insulated from the wires that
carry the power. The isolation is provided by the insulation of the wires. However, if the wire
insulation gets damaged and makes contact to the casing, the casing will be at the high voltage
supplied by the wires. If the user touches the instrument he or she will feel the high voltage. If, while
standing on a wet floor, a user simultaneously comes in contact with the instrument case and a pipe or
faucet connected to ground, a sizable current can flow through him or he. However, if the case is
connected to the ground by use of a third (ground) wire, the current will flow from the hot wire
directly to the ground and bypass the user.
Equipments with a three wire cord is thus much safer to use. The ground wire (3rd wire) which is
connected to metal case, is also connected to the earth ground (usually a pipe or bar in the ground)
through the wall plug outlet.
Always observe the following safety precautions when working in the laboratory:
1. Do not work alone while working with high voltages or on energized electrical equipment or
electrically operated machinery like a drill.
2. Power must be switched off whenever an experiment or project is being assembled, disassembled,
or modified. Discharge any high voltage points to grounds with a well insulated jumper.
3. Remember that capacitors can store dangerous quantities of energy.
4. Make measurements on live circuits or discharge capacitors with well insulated probes keeping
one hand behind your back or in your pocket. Do not allow any part of your body to contact any
part of the circuit or equipment connected to the circuit.
5. After switching power off, discharge any capacitors that were in the circuit. Do not trust
supposedly discharged capacitors. Certain types of capacitors can build up a residual charge after
being discharged. Use a shorting bar across the capacitor, and keep it connected until ready for
use. If you use electrolytic capacitors, do not:
put excessive voltage across them
put ac across them
connect them in reverse polarity
6. Take extreme care when using tools that can cause short circuits if accidental contact is made to
other circuit elements. Only tools with insulated handles should be used.
7. If a person comes in contact with a high voltage, immediately shut off power. Do not attempt to
remove a person in contact with a high voltage unless you are insulated from them. If the victim is
not breathing, apply CPR immediately continuing until he/she is revived, and have someone dial
emergency numbers for assistance.
8. Check wire current carrying capacity if you will be using high currents. Also make sure your
leads are rated to withstand the voltages you are using. This includes instrument leads.
9. Avoid simultaneous touching of any metal chassis used as an enclosure for your circuits and any
pipes in the laboratory that may make contact with the earth, such as a water pipe. Use a floating
voltmeter to measure the voltage from ground to the chassis to see if a hazardous potential
difference exists.
10. Make sure that the lab instruments are at ground potential by using the ground terminal supplied
on the instrument. Never handle wet, damp, or ungrounded electrical equipment.
11. Never touch electrical equipment while standing on a damp or metal floor.
12. Wearing a ring or watch can be hazardous in an electrical lab since such items make good
electrodes for the human body.
13. When using rotating machinery, place neckties or necklaces inside your shirt or, better yet,
remove them.
14. Never open field circuits of D-C motors because the resulting dangerously high speeds may cause
a "mechanical explosion".
15. Keep your eyes away from arcing points. High intensity arcs may seriously impair your vision or
a shower of molten copper may cause permanent eye injury.
16. Never operate the black circuit breakers on the main and branch circuit panels.
17. In an emergency all power in the laboratory can be switched off by depressing the large red
button on the main breaker panel. Locate it. It is to be used for emergencies only.
18. Chairs and stools should be kept under benches when not in use. Sit upright on chairs or stools
keeping the feet on the floor. Be alert for wet floors near the stools.
19. Horseplay, running, or practical jokes must not occur in the laboratory.
20. Never use water on an electrical fire. If possible switch power off, then use CO2 or a dry type fire
extinguisher. Locate extinguishers and read operating instructions before an emergency occurs.
21. Never plunge for a falling part of a live circuit such as leads or measuring equipment.
22. Never touch even one wire of a circuit; it may be hot.
23. Avoid heat dissipating surfaces of high wattage resistors and loads because they can cause severe
burns.
24. Keep clear of rotating machinery.
Precautionary steps before starting an experiment so as not to waste time allocated
a) Read materials related to experiment before hand as preparation for pre-lab quiz and experimental
calculation.
b) Make sure that apparatus to be used are in good condition. Seek help from technicians or the lab
demonstrator in charge should any problem arises.
Power supply is working properly ie Imax (maximum current) LED indicator is disable.
Maximum current will retard the dial movement and eventually damage the equipment.
Two factors that will light up the LED indicator are short circuit and insufficient supply
of current by the equipment itself. To monitor and maintain a constant power supply, the
equipment must be connected to circuit during voltage measurement. DMM are not to be
used simultaneously with oscilloscope to avert wrong results.
Digital multimeter (DMM) with low battery indicated is not to be used. By proper
connection, check fuses functionality (especially important for current measurement).
Comprehend the use of DMM for various functions. Verify measurements obtained with
theoretical values calculated as it is quite often where 2 decimal point reading and 3
decimal point reading are very much deviated.
The functionality of voltage waveform generators are to be understood. Make sure that
frequency desired is displayed by selecting appropriate multiplier knob. Improper settings
(ie selected knob is not set at minimum (in direction of CAL – calibrate) at the bottom of
knob) might result in misleading values and hence incorrect results. Avoid connecting
oscilloscope together with DMM as this will lead to erroneous result.
Make sure both analog and digital oscilloscopes are properly calibrated by positioning
sweep variables for VOLT / DIV in direction of CAL. Calibration can also be achieved
by stand alone operation where coaxial cable connects CH1 to bottom left hand terminal
of oscilloscope. This procedure also verifies coaxial cable continuity.
c) Internal circuitry configuration of breadboard or Vero board should be at students’ fingertips (ie
holes are connected horizontally not vertically for the main part with engravings disconnecting in-
line holes).
d) Students should be rest assured that measured values (theoretical values) of discrete components
retrieved ie resistor, capacitor and inductor are in accordance the required ones.
e) Continuity check of connecter or wire using DMM should be performed prior to proceeding an
experiment. Minimize wires usage to avert mistakes.
PREFACE
The EC1015 Linear Integrated Circuits Lab is designed to help students understand the
basic principles of Operational amplifier circuits as well as giving them the insight on design,
simulation and hardware implementation of circuits. The main aim is to provide hands-on
experience to the students so that they are able to put theoretical concepts to practice.
The content of this course consists of two parts, ‘simulation’ and ‘hardwired’.
Computer simulation is stressed upon as it is a key analysis tool of engineering design.
“OrCAD Pspice and OrCAD Capture” software is used for simulation of Operational
amplifier circuits.
Students will carry out design experiments as a part of the experiments list provided
in this lab manual. Students will be given a specific design problem, which after completion
they will verify using the simulation software or hardwired implementation.
LIST OF EXPERIMENTS
Exp. No Title
1
Basic op-amp circuits
Inverting , Non-inverting voltage amplifiers & voltage
follower
2Linear op-amp circuits
Differentiator & Integrator
3Non-linear op-amp circuits
Precision Rectifiers(Half wave rectifier & full wave rectifier)
4 Comparator(Basic comparator & Schmitt trigger)
5Oscillators
RC Phase shift Oscillator and Wein bridge Oscillator
6IC555 Timer
Astable and Monostable operation
7DAC
Weighted Resistor & R-2R ladder types
8 AC Amplifiers(Inverting & Non-Inverting amplifiers)
9Op-amp applications- Adder, Clipper, Clamper, Square wave
generator
10Active Filters
LPF, HPF, BPF & BSF
INTRODUCTION TO ANALOG SYSTEM LAB KIT (ALSK) PRO
Part I – Learning the basics
In the first part, the students will be exposed to the operation of the basic building blocks of
analog systems. Using the general purpose operational amplifiers and the precision analog
multiplier, the student will build gain stages, buffers, instrumentation amplifiers and voltage
regulators. These experiments bring out several important issues, such as measurement of
gain-bandwidth product, slew-rate, as well as saturation limits of the operational amplifiers.
Part II – Building analog systems
In the second part, the students will be focused on learning about analog systems. Integrators
and differentiators will be introduced, which are essential for implementing filters that can
band-limit a signal prior to the sampling process to avoid aliasing errors.
System Lab Kit overview
ASLK PRO has been developed at Texas Instruments India. This kit is designed for
undergraduate engineering students to perform analog lab experiments. The main idea behind
ASLK PRO is to provide a cost efficient platform or test bed for students to realize almost
any analog system using general purpose ICs such as OP-Amps and analog multipliers.
ASLK PRO comes with three general-purpose operational amplifiers (TL082) and three
wide-bandwidth precision analog multipliers (MPY634) from Texas Instruments. We have
also included two 12-bit parallel-input multiplying digital-to-analog converters DAC7821, a
wide-input non-synchronous buck-type DC/DC controller TPS40200, and a low dropout
regulator TPS7250 from Texas Instruments. A portion of ASLK PRO is left for general-
purpose prototyping which can be used for carrying out mini-projects.
The kit has a provision to connect ±10V DC power supply. The kit comes with the necessary
short and long connectors. This comprehensive user manual included with the kit gives
complete insight of how to use ASLK PRO. The manual covers exercises of analog system
design along with brief theory and simulation results.
The following software is necessary to carry out the experiments suggested in this manual.
1. TINA or PSpice or any powerful simulator based on the SPICE Simulation Engine
2. FilterPro - A software program for designing analog filters
3. SwitcherPro - A software program for designing power supplies
The Analog System Lab kit ASLK PRO is divided into many sections. Refer to the photo of
ASLK PRO when you read the following description.
There are three TL082 OP-Amp ICs labelled 1, 2, 3 on ASLK PRO. Each of these ICs has
two amplifiers, which are labelled A and B. Thus 1A and 1B are the two OP-AMps on OP-
AMP IC 1, etc. The six OP-amps are categorized as below.
OP-Amp Type Purpose
1A TYPE I Inverting Configuration only
1B TYPE I Inverting Configuration only
2A TYPE II Full Configuration
2B TYPE II Full Configuration
3A TYPE III Basic Configuration
3B TYPE III Basic Configuration
Thus, the OP-amps are marked TYPE I, TYPE II and TYPE III on the board. The OP-Amps
marked TYPE I can be connected in the inverting configuration only. With the help of
connectors, either resistors or capacitors can be used in the feedback loop of the amplifier.
There are two such TYPE I amplifiers. There are two TYPE II amplifiers which can be
configured to act as inverting or non-inverting. Finally, we have two TYPE III amplifiers
which can be used as voltage buffers. Three analog multipliers are included in the kit. These
are wide-bandwidth precision analog multipliers from Texas Instruments (MPY634). Each
multiplier is a 14-pin IC and operates on internally provided ±10V supply.
There are two digital-to-analog converters (DAC) provided in the kit, labeled DAC I and
DAC II. Both the DACs are DAC7821 from Texas Instruments. They are 12-bit, parallel-
input multiplying DACs which can be used in place of analog multipliers in circuits like
AGC/AVC. Ground and power supplies are provided internally to the DAC. DAC Logic
Supply Jumper can be used to connect logic power supplies of both DAC I and DAC II to
either LDO or DC/DC converter located on the board. Using Tri-state switches you can set
12-bits of input data for each DAC to desired value. Click the Latch Data button to trigger
Digital-to-analog conversion.
We have included a wide-input non-synchronous DC/DC buck converter TPS40200 from
Texas Instruments on ASLK PRO. The converter provides an output of 3.3V over a wide
input range of 5.5-15V at output currents ranging from 0.125A to 2.5A. Using Vout SEL
jumper you can select output voltage to be either 5V or 3.3V. Another jumper allows you to
select whether input voltage is provided from the board (+10V), or externally using screw
terminals. We have included two transistor sockets on the board, which are needed in
designing an LDO regulator, or custom experiments.
A specialized LDO regulator IC (TPS7250) has been included on the board, which can
provide a constant output voltage for input voltage ranging from 5.5V to 11V. Ground
connection is internally provided to the IC. Using ON/OFF jumper you can enable or disable
LDO IC. Another jumper allows you to select whether input voltage is provided from the
board (+10V), or externally using screw terminals.
There are two 1kX trimmers (potentiometer) in the kit to enable the designer to obtain a
variable voltage if needed for a circuit. The potentiometers are labeled P1 and P2. These
operate respectively in the range 0V to +10V, and -10V to 0V. The kit has screw terminals to
connect ±10V power supply. All the ICs on the board are internally connected to power
supply. e sockets on the board, which can be used as rectifiers in custom laboratory
experiments. The top right portion of the kit is a general-purpose area which can be used as a
proto-board. ± 10V points and GND are provided for this area.
Lab Setup
ASLK PRO and the associated Lab Manual from Texas Instruments India – the lab kit comes
with required connectors. We provide an experiment that helps you build a circuit to directly
interface analog outputs to an oscilloscope. Dual power supply with the operating voltages of
±10V. Function generators which can operate in the range on 1 to 10 MHz and capable of
generating sine, square and triangular waves. A computer with installed circuit simulation
software. When we do not explicitly mention the magnitude and frequency of the input
waveform, please use 0 to 1V as the amplitude of the input and 1 kHz as the frequency.
Always use sinusoidal input when you plot the frequency response and use square wave input
when you plot the transient response.
Precaution! Please note that TL082 is a dual OP-Amp. This means that the IC has two OP-
Amp circuits. If your experiment requires only one of the two ICs, do not leave the inputs and
output of the other OP- Amp open; instead, place the second OP-Amp in unity-gain mode and
ground the inputs.
1. BASIC OP-AMP CIRCUITS
1.1 OBJECTIVE
1. To design the following basic op-amp circuits and explain the operation of each:
a. Inverting amplifier
b. Non-inverting amplifier
c. Voltage follower
1.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/Value Quantity
1 IC 741 Refer data sheet in
appendix
1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 1
3 Resistors 1.5K Ω 2
4 Dual Regulated power supply (0 -30V), 1A 1
5 Function Generator (0-2) MHz 1
6 ASLK PRO Kit Refer data sheet in
appendix
1
1.3THEORY
An op-amp is a high gain, direct coupled differential linear amplifier choose response
characteristics are externally controlled by negative feedback from the output to input, op-
amp has very high input impedance, typically a few mega ohms and low output impedance,
less than 100.
Op-amps can perform mathematical operations like summation integration,
differentiation, logarithm, anti-logarithm, etc., and hence the name operational amplifier op-
amps are also used as video and audio amplifiers, oscillators and so on, in communication
electronics, in instrumentation and control, in medical electronics, etc.
1.3.1 Circuit symbol and op-amp terminals
The circuit schematic of an op-amp is a triangle as shown below in Fig. 1-1 op-amp
has two input terminal. The minus input, marked (-) is the inverting input. A signal applied to
the minus terminal will be shifted in phase 180o at the output. The plus input, marked (+) is
the non-inverting input. A signal applied to the plus terminal will appear in the same phase at
the output as at the input. +VCC denotes the positive and negative power supplies. Most op-
amps operate with a wide range of supply voltages. A dual power supply of +15V is quite
common in practical op-amp circuits. The use of the positive and negative supply voltages
allows the output of the op-amp to swing in both positive and negative directions.
Fig-1-1 op-amp circuit symbol
1.3.2 Op amp internal circuit
Commercial integrated circuit OP-amps usually consists of your cascaded blocks as shown in
figure 1-2shown below.
V2
non-invertinginput
output-
-Vcc
inverting input
+offset null
+Vcc
offset null
u A 7 4 1
Differential Amplifier
Differential Amplifier
Buffer and Level
Translator Output driver
V1
Fig 1-2Internal block schematic op-amp
The first two stages are cascaded difference amplifier used to provide high gain. The third
stage is a buffer and the last stage is the output driver. The buffer is usually an emitter
fallowing whose input impedance is very high so that it prevents loading of the high gain
stage. The output stage is designed to provide low output impedance. The buffer stage along
with the output stage also acts as a level shifter so that output voltage is zero for zero inputs.
In this laboratory experiment, you will learn several basic ways in which an op-amp
can be connected using negative feedback to stabilize the gain and increase the frequency
response. The extremely high open-loop gain of an op-amp creates an unstable situation
because a small noise voltage on the input can be amplified to a point where the amplifier in
driven out of its linear region. Also unwanted oscillations can occur. In addition, the open-
loop gain parameter of an op-amp can vary greatly from one device to the next. Negative
feedback takes a portion of output and applies it back out of phase with the input, creating an
effective reduction in gain. This closed-loop gain is usually much less than the open-loop
gain and independent of it.
1.3.3 Closed – loop voltage gain, ACL
The closed-loop voltage gain is the voltage gain of an op-amp with external feedback.
The amplifier configuration consists of the op-amp and an external negative feedback circuit
that connects the output to the inverting input. The closed loop voltage gain is determined by
the external component values and can be precisely controlled by them.
1.3.4 Non-inverting amplifier
An op-amp connected in a closed-loop configuration as a non-inverting amplifier with
a controlled amount of voltage gain is shown in Fig 1-3.
-V c c
R f
R 1
V o
V in
u A 7 4 1
+V c c
-
+
Fig. 1-3 Non-inverting amplifier configuration of op-amp
The input signal is applied to the non-inverting (+) input. The output is applied back to the
inverting(-) input through the feedback circuit (closed loop) formed by the input resistor R1
and the feedback resistor Rf. This creates negative feedback as follows. Resistors R1 and Rf
form a voltage-divider circuit, which reduces VO and connects the reduced voltage Vf to the
inverting input. The feedback is expressed as
V f=(R1
R1+R f)Vo
The difference of the input voltage, Vin and the feedback voltage, Vfis the differential input of
the op-amp. This differential voltage is amplified by the gain of the op-amp and produces an
output voltage expressed as
Vo=(1+ R f
R1)V in
The closed-loop gain of the non-inverting amplifier is, thus
ACL(NI )=1+R f
R1
Notice that the closed loop gain is
independent of open-loop gain of op-amp
set by selecting values of R1 and Rf
An expression for the input impedance of a non-inverting amplifier can be written as
Zin (NI )=(1+AOL β )Z in
Where AOL = open-loop voltage gain of op-amp
Zin = internal input impedance of op-amp (without feedback)
= attenuation of the feedback circuit
=V f
Vo=
R1
R1+R f
Above equation shows that the input impedance of the non-inverting amplifier configuration
with negative feedback is much greater than the internal output impedance of the op-amp
itself.
The output impedance of a Non-Inverting amplifier can be written as
Zo(NI )
= Zo1+AOL β
This equation shows that the output impedance of non-inverting amplifier is much less than
the internal output impedance, Zo of the op-amp.
1.3.5 Voltage follower
The voltage follower configuration is a special case of the non-inverting amplifier
where all the output voltage is feedback to the inverting input by straight connection, as
shown in fig. 1.4
Fig. 1.4 Voltage follower configuration of op-amp
As you can see, the straight feedback connection has a voltage gain of (which means there is
no gain).
ACL (VF) = 1
The most important features of the voltage follower configuration are its very high input
impedance and its very low output impedance. These features make it a nearly ideal buffer
amplifier for interfacing high-impedance sources and low-impedance loads.
Z IN (VF )=(1+AOL)Z in
ZO (VF )=ZO
1+AOL
As you can see, the voltage follower input impedance is greater for a given AOL and Zin than
for the non-inverting amplifier. Also, its output impedance is much smaller.
+V c c
+
-V c c
u A 74 1-
V o
V in
1.3.6. Inverting amplifier
An op-amp connected as an inverting amplifier with a controlled amount of voltage
gain is shown in fig. 1.5
Fig.1.5 inverting amplifier
The input signal is applied through a series input resistor R1 to the inverting input. Also, the
output is fed back through Rf to the same input. The non-inverting input is grounded. An
expression for the output voltage of the inverting amplifier is written as
V O=−R f
R1V in
The –ve sign indicates inversion. The closed-loop gain of the inverting amplifier is, thus
ACL ( I )=−R f
R1
The input & output impedances of an inverting amplifier are
Zin(I) = R1
ZO ( I )=Zo
1+AOL β
The output impedance of both the non-inverting and inverting amplifier configurations is
very low; in fact, it is almost zero in practical cases. Because of this near zero output
impedance, any load impedance connected to the op-amp output can vary greatly and not
change the output voltage at all.
1.3.7. Design Constraints
The output signal is limited by the IC's power sources: the output signal cannot be greater
than +15V.
R 1
R f
V in
+V c c
u A 7 4 1-
+
-V c c
V o
1.4 PRE LAB QUESTIONS
2. Identify each of the op-amp configurations
Fig.(a)
3. A non-inverting amplifier has R1 of 1K&Rfof 100K. Determine Vf and
(Feedback voltage and feedback fraction), if VO = 5V
4. For the amplifier in Fig.(b) determine the following: (a) ACL(NI) (b) VO (c) Vf
Vin
+Vcc
+
-Vcc
u A 7 4 1-
Vo
-Vcc
R f
R 1
Vo
Vin
u A 74 1
+Vcc
-
+
R 1
R f
Vin+Vcc
u A 7 4 1-
+
-Vcc
Vo
+Vcc
u A 7 4 1 Vo
+
-Vcc
R f = 5 6 0 k
R 1 = 1 . 5 k
-
Vin10 mVrms
Fig.(b)
1.5 EXPERIMENT
(1) Non-Inverting amplifier
1.1 Design a non-inverting amplifier for the gain of 15. Let R1=1.5k Assemble the circuit.
1.2 Feed sinusoidal input of amplitude 10V and frequency 1KHz
1.3 Observe the input voltage and output voltage on a CRO. Tabulate the reading in Table
(2) Voltage follower
2.1 Assemble a voltage follower circuit.
2.2 Feed sinusoidal input of amplitude 100V and frequency 1KHz.
2.3 Observe the input and output voltages on a CRO. Tabulate the readings in Table.
(3) Inverting amplifier
3.1 Design an inverting amplifier for the gain of 15. Let R1=1.5k. Assemble the circuit.
3.2 Feed sinusoidal input of amplitude 1V and frequency 1KHz.
3.3 Observe the input and output voltages on a CRO. Tabulate the readings in Table
op-amp
configuration
/ circuit
Input signal Output signal Voltage gain
Amplitude Frequency Amplitude FrequencyDesigned
value
Observed
value
Non-inverting
amplifier
Voltage
follower
Inverting
amplifier
1.6. POST LAB QUESTIONS
1. What is the relationship, if any, between the polarity of the output and input voltages in
your experimental op-amp? Refer to your data.
2. Comment on the statement: “The closed-loop gain-bandwidth product is a constant for a
given op-amp”.
3. Find the value of Rf that will produce closed-loop gain of 300 in each amplifier in
fig.(c)
Fig.(c)
4. Determine the approximate values for each of the following quantities in Fig.(d).
Fig.(d)
5. If a signal voltage of 10mV is applied to each amplifier in Fig.(e),
what are the output voltages?
R f
u A 74 1
-Vcc
+
-
+Vcc
Vin
R 1 = 2 . 2k
Vo
R f
+Vcc
-Vcc
-Vou A 7 4 1
+
R 1 = 1 2 k
Vin
Ii n-- ---
+
R f = 2 2 k
V o
V in1 V
R 1 = 2 . 2 k
-
If
u A 7 4 1
+Vcc
-Vcc
-----
R f =1 0 0 k
uA 7 4 1
-Vcc
+
-
+Vcc
Vin
R 1 = 1 0 0 k
Vo
Fig. (e)
Vin
+Vcc
+
-Vcc
u A 7 4 1-
Vo
-V c c
R f =1 M
R 1 =4 7 k
V o
V in
u A 7 4 1
+V c c
-
+
+
-V c cR 1 =1 0 k
R f = 1 0 k
R 1 =1 0 k
-V in
+V c c
u A 7 4 1R 2 =1 0 k
V o
R 2 =1 k
V in-
R f =1 0 0 k
+
+V c cR 1 =1 k
V ou A 7 4 1
-V c c
2. LINEAR OP-AMP CIRCUITS
2.1 OBJECTIVE
1. Design an integrator for a frequency of 1KHz, given R=1KΩ , C=0.1 µF and Rf
= 1MΩ. Conduct the experiment and plot integrated output waveforms for various
input waveforms and analyze
2. Design an differentiator for a frequency of 1KHz, given R=10KΩ , and C=0.1µf
and Rf = 470Ω. Conduct the experiment and plot integrated output waveforms for
various input waveforms and analyze
2.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/Value Quantity1 IC 741 Refer data sheet in
appendix1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 13 Resistors 1K Ω
1M Ω10 K Ω470 Ω
1111
4 Capacitors 0.1µf 2
5 Dual Regulated power supply (0 -30V), 1A 16 Function Generator (0-2) MHz 17 ASLK PRO Kit 1
2.3 THEORY
In this laboratory experiment, you will learn several basic ways in which an op-amp
can be connected using negative feedback to stabilize the gain and increase the frequency
response. The extremely high open-loop gain of an op-amp creates an unstable situation
because a small noise voltage on the input can be amplified to a point where the amplifier in
driven out of its linear region. Also unwanted oscillations can occur. In addition, the open-
loop gain parameter of an op-amp can vary greatly from one device to the next. Negative
feedback takes a portion of output and applies it back out of phase with the input, creating an
effective reduction in gain. This closed-loop gain is usually much less than the open-loop
gain and independent of it.
2.3.1 Integrator
An op-amp integrator simulates mathematical integration which is basically a
summing process that determines the total area under the curve of a function ie., the
integrator does integration of the input voltage waveform. Here the input element is resistor
and the feedback element is capacitor as shown in fig.2-1.
Fig.2-1 Basic op-amp integrator
The output voltage is given by
V O=− 1RC∫o
t
V S dt+V C ( t=0 )
Where VC (t=0) is the initial voltage on the capacitor. For proper integration, RC has to be
much greater than the time period of the input signal.
It can be seen that the gain of the integrator decreases with the increasing frequency
so, the integrator circuit does not have any high frequency problem unlike a differentiator
circuit. However, at low frequencies such as at dc, the gain becomes infinite. Hence the op-
amp saturates (ie., the capacitor is fully charged and it behaves like an open circuit). A
practical integrator circuit is shown in Fig. 2-2.
Fig. 2-2 Practical op-amp integrator
2.3.2 Differentiator
An op-amp differentiator simulates mathematical differentiation, which is a process of
determining the instantaneous rate of change of a function. Differentiator performs the
reverse of integration function. The output waveform is derivative of the input waveform.
C
V ou A 7 4 1
R
-V in
+V c c
+
-V c c
C
R f
V ou A 7 41
R
-V in
+V c c
+
-V c c
Here, the input element is a capacitor and the feedback element is a resistor. An ideal
differentiation is shown in fig. 2-3.
Fig.2-3 Basic op-amp differentiator
The output voltage is given by
V O=−RC (dV S
dt)
For proper differentiation, RC has to be much smaller than the time period of the input signal.
It can be seen that at high frequencies a differentiator may become unstable and break into
oscillation. Also, the input impedance of the differentiator decreases with increase in
frequency, thereby making the circuit sensitive to high frequency noise. So, in order to limit
the gain of the differentiator at high frequencies, the input capacitor is connected in series
with a resistance R1 and hence avoiding high frequency noise and stability problems. A
practical differentiator circuit is shown in fig. 2-4.
Fig. 2-4 Practical op-amp differentiator
u A 7 4 1
V in
-V c c
V o
+
-
C
R f
+V c c
2.3.3 Design Constraints
Integrator circuit
The output of the integrator cannot rise indefinitely as the output will be limited.
The output of the op amp integrator will be limited by supply voltage.
When designing one of these circuits, it may be necessary to limit the gain or increase
the supply voltage to accommodate the likely output voltage swings.
While small input voltages and for short times may be acceptable, care must be taken
when designing circuits where the input voltages are maintained over longer periods of
time.
Differentiator circuit
Output rises with frequency: One of the key facts of having a series capacitor is that
it has an increased frequency response at higher frequencies. The differentiator output
rises linearly with frequency, although at some stage the limitations of the op amp will
mean this does not hold good. Accordingly precautions may need to be made to account
for this. The circuit, for example will be very susceptible to high frequency noise, stray
pick-up, etc.
Component value limits: It is always best to keep the values of the capacitor and
particularly the resistor within sensible limits. Often values of less than 100kΩ for the
resistor are best. In this way the input impedance of the op amp should have no effect
on the operation of the circuit.\
2.4 PRE LAB QUESTIONS
1. Determine the input and output impedances for each amplifier configuration, (Z in=10M,
ZO=75, AOL = 175,000) in fig.(a)
Fig. (a)
2. Determine the BW of each of the amplifiers in fig(b). The op-amps have an open-loop
gain of 90dB and a unity gain bound width of 2MHz.
-V c c
R f =5 6 0 k
R 1 =2 . 7 k
V o
V in
u A 7 4 1
+V c c
-
+Vin
+Vcc
+
-Vcc
uA 7 41-
Vo
R f =1 5 0k
u A 7 4 1
-V c c
+
-
+V c c
V in
R 1 =1 0 k
V o
Fig.(b)
3. Determine the output voltage of each amplifier in Fig (c).
Fig.(c)
-V c c
R f =2 2 0 k
R 1 =3 .3 k
V o
V in
u A 7 4 1
+V c c
-
+
R f =4 7 k
u A 7 4 1
-V c c
+
-
+V c c
V in
R 1 =1 k
V o
1 k
8V-
R f =1 0 k
+
+V c c1V
1 k
V o
3V
u A 7 4 1
-V c c
1 k
0.2V
-
+V c c
+
1 k
0.5V
-V c c
1 kV ou A 7 4 1
R f =1 0 k
100 k
3V
4V
-
100 k
R f =2 5 k
+
+V c c2V
100 k
V o
1V
u A 7 4 1
-V c c
100 k100 k
8V-
R f =1 0 k
+
+V c c2V
47 k
V o
3V
u A 7 4 1
-V c c
10 k
V o-
R f =1 0 0 k
2V
R 1 =1 0 k
R f =1 0 0 k
-V c c
+
+V c cR 1 =1 0 k
3V
u A 7 4 1
V o-
R f = 10 k
2V
R 1 =1 0 k
R f = 10 k
-V c c
+
+V c cR 1 =1 0 k
3V
uA 7 4 1
2.5 EXPERIMENT
(1) Integrator
1.1 Assemble an integrator circuit with R=1K and C=0.1µf. Connect Rf of value 1M
across the capacitor.
1.2 Feed +1V, 500Hz square wave input.
1.3 Observe the input and output voltages on a CRO.
1.4 Determine the gain of the circuit and tabulate the readings in table. Model waveform is
shown.
1.5 Plot the input and output voltages on the same scale on a linear graph sheet.
(2) Differentiator
2.1 Assemble a differentiator circuit with R=10K and C=0.1µf. Connect a resistor R1 of
value 470 between the source and the capacitor.
2.2 Feed +1V, 500Hz square wave input.
2.3 Observe the input and output voltages on a CRO.
op-amp
configuration /
circuit
Input signal Output signal
Amplitude Frequency Amplitude Frequency
Integrator
Differentiator
2.4 Determine the gain of the circuit and tabulate the readings in table. Model waveform is
shown.
2.5 Plot the input and output voltages on the same scale on a linear graph sheet.
a)
(b)
Fig.2.5 Waveform for (a) op-amp integrator, (b) op-amp differentiator
2.6 POST LAB QUESTIONS
1. Determine the gain-bandwidth product of each amplifier.
2. Determine the input and output impedances of each amplifier.
3. (a) What is the normal output voltage in fig. 2-14?
(b) What is the output voltage of R2 opens?
(c) What happens if R5 opens?
Fig. 2-14
R f =1 0 k
u A 7 4 1
R 30 . 9 1 k
-V c c
+
-
+V c cV in
R 1 = 1 k
V o
10k
0.2V
10 k
-
1 0 k
+
+V c c
0.1V
0.5V
10k
V o
1V
u A 7 4 1
-V c c
10 k
3. NON- LINEAR OP-AMP CIRCUITS
3.1 OBJECTIVE
a. To study the operation of active diode circuits (precisions circuits) using op-amps, such as
half wave rectifier and full wave rectifier
3.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/
Value
Quantity
1 IC 741 Refer data sheet in
appendix
1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 1
3 Resistors 10 K Ω 6
4 Semiconductor(Diode) 1N4002 2
5 Dual Regulated power supply (0 -30V), 1A 1
6 Function Generator (0-2) MHz 1
7 ASLK PRO Kit Refer data sheet in
appendix
1
3.3 THEORY
The major limitation of ordinary diodes is that it cannot rectify voltage below 0.6v,
thecut in voltage of the diode. The precision rectifier, which is also known as a super
diode, is a configuration obtained with an operational amplifier in order to have a circuit
behaving like an ideal diode and rectifier. It can be useful for high-precision signal
processing.
3.3.1 Active Half Wave Rectifier
Op-amps can enhance the performance of diode circuits. For one thing, the op-amp
can eliminate the effect of diode offset voltage, allowing us to rectify, peak-detect, clip, and
clamp low-level signals (those with amplitudes smaller than the offset voltage). And because
of their buffering action op-amps can eliminate the effects of source and load on diode
circuits. Circuits that combine op-amps and diodes are called active diode circuits. Fig. (a)
shows an active HWR, with gain.
Vi
+ D1
uA741 Vo
- R1
RL
R2
Fig(a) Active HWR, (b) input and output waveforms
When the input signal goes positive, the op-amp goes positive and turns on the diode. The
circuit then acts as a conventional non-inverting amplifier, and the positive half-cycle
appears across the load resistor. On the other hand, when the input goes negative, the op-
amp output goes negative and turns off the diode. Since the diode is open, no voltage
appears across the load resistor. This is why the final output is almost a perfect half-wave
signal.
The high gain of the op-amp virtually eliminates the effect of offset voltage. For
instance, if the offset voltage equals 0.7V and open-loop gain is 100,000, the input that just
turns on the diode is
Vin
0.7V
7 V .100,000
When the input is greater than 7µV, the diode turns on and the circuit acts like a voltage
follower. The effect is equivalent to reducing the offset voltage by a factor of A.
The active HWR is useful with low-level signals. For instance, if we want to
measure sinusoidal voltages in the millivolt region, we can add a milli ammeter in series
with RL with the proper value of RL, we can calibrate the meter to indicate rms millivolts.
1.3.2 Design Constraints
The output signal is limited by the IC's power sources: the output signal cannot be
greater than +15V
3.3.3 Experiment
1. Connect the circuit as shown in the figure. Consider all resistors value 10kΩ . Use
1N4002 diodes. Assemble the circuit.
2. Feed sinusoidal input of amplitude 200mVPP and frequency 100Hz. Using a CRO
observe the input and output voltages simultaneously. Determine the amplitude and
frequency of the output voltage.
3. Increase the frequency of the input signal till distortion appears in the output. Record
this frequency in the below table
4. Plot the input and output voltages on the same scale.
3.3.4 Full Wave Rectifier
A Full Wave Rectifier is a circuit, which converts an ac voltage into a pulsating dc
voltage using both half cycles of the applied ac voltage. It uses two diodes of which one
conducts during one half cycle while the other conducts during the other half cycle of the
applied ac voltage.
During the positive half cycle of the input voltage, diode D1 becomes forward
biased and D2 becomes reverse biased. Hence D1 conducts and D2 remains OFF. The
load current flows through D1 and the voltage drop across RL will be equal to the input
voltage. During the negative half cycle of the input voltage, diode D1 becomes reverse
biased and D2 becomes forward biased. Hence D1 remains OFF and D2 conducts. The
load current flows through D2 and the voltage drop across RL will be equal to the input
voltage.
Particulars Amplitude Time period Frequency
Input Voltage
Output Voltage
\
Input waveform
Output waveform:
Fig (a) Full wave rectifier, (b) input and output waveforms
Experiment1. Connect the circuit as shown in the figure. Consider all resistors value 10kΩ . Use
1N4002 diodes. Assemble the circuit.
2. Feed sinusoidal input of amplitude 200mVPP and frequency 100Hz.
3. Using a CRO observe the input and output voltages simultaneously. Determine the
amplitude and frequency of the output voltage. Increase the frequency of the input signal
till distortion appears in the output. Record this frequency in the below table.
4. Plot the input and output voltages on the same scale.
Particulars Amplitude Time period Frequency
Input Voltage
Output Voltage
3.4 PRE-LAB QUESTIONS
1. What is a precision diode
2. Give the uses of precision diode
3. Give some applications of precision diode
4. What are the major limitations of an ordinary diode?
5. For a precision HWR, draw the output waveform if Vin is a 300mV peak sine wave at
1 KHz.
3.5 POST LAB QUESTIONS
1. If the diode is reversed in half wave rectifier, what would the output voltage be?
2. Draw the equivalent circuit of a full wave rectifier for input voltage less than zero
volts(Vi<0)
3. Draw the circuit of a Clipper which will clip the input signal below a reference voltage.
4. What is Clamper circuit?
4. COMPARATOR4.1 OBJECTIVE:
1. Design the comparator for a frequency of 1 KHz sine wave with 5 Vpp at the non-
inverting input terminal and apply 1V dc voltage as reference voltage at the inverting
terminal of IC741
2. Design a Schmitt Trigger and conduct an experiment to obtain VUTP and VLTP for various
values of R1 and R2 for the specified design constraint with upper and lower threshold
should be ±1V, for the frequency range of 100 Hz to 10KHz.
4.2 COMPARATOR
4.2.1 Apparatus required:
S.No Equipment/Component name Specifications/Value Quantity
1 IC 741 Refer data sheet 1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 1
3 Multimeter 1
4 Resistors 10 kΩ 2
6 Dual Regulated power supply (0 -30V), 1A 1
4.2.2 Theory:
A Comparator is a non-linear signal processor. It is an open loop mode application of
Op-amp operated in saturation mode. Comparator compares a signal voltage at one input with
a reference voltage at the other input. Here the Op-amp is operated in open loop mode and
hence the output is ±Vsat. It is basically classified as inverting and non-inverting comparator.
In a non-inverting comparator Vin is given to +ve terminal and Vref to –ve terminal. When
Vin < Vref, the output is –Vsat and when Vin > Vref, the output is +Vsat (see expected
waveforms). In an inverting comparator input is given to the inverting terminal and reference
voltage is given to the non inverting terminal. The output of the inverting comparator is the
inverse of the output of non-inverting comparator. The comparator can be used as a zero
crossing detector, window detector, time marker generator and phase meter
.
4.2.3 Experiment
1. Connect the components/equipment as shown in the circuit diagram.
2. Switch ON the power supply.
3. Apply 1 KHz sine wave with 5 Vpp at the non-inverting input terminal of IC741 using a
function generator.
4. Apply 1V dc voltage as reference voltage at the inverting terminal of IC741.
5. Connect the channel-1 of CRO at the input terminals and channel-2 of CRO at the
output terminals.
6. Observe the input sinusoidal signal at channel-1 and the corresponding output square
wave at channel-2 of CRO. Note down their amplitude and time period.
7. Overlap both the input and output waves and note down voltages at positions on sine
wave where the output changes its state. These voltages denote the Reference voltage.
8. Plot the output square wave corresponding to the sine input with Vref = 1V.
4.2.4 Expected Waveforms: Comparator Input & Output Waveforms
Observations
Theoretical Reference voltage (From the circuit)
Practical Reference voltage (From output waveform)
4.2.5 Pre Lab Question:
1. How many basic input parameters are required for a comparator?
2. How is Vo related to Vin and Vref?
3. Why this circuit is called a non-inverting comparator?
4. What do these maximum and minimum values correspond to?
4.2.6 Post Lab Question:
1. Draw the circuit diagram of a non-inverting comparator and inverting comparator.
2. What do you think is the role of resistors R1 and R2?
3. What is the output of a non-inverting comparator and inverting comparator if the
input is triangular signal?
4. What happens when Vref becomes greater than the maximum value of Vin?
5. What happens when Vref becomes less than the minimum value of Vin?
Result:
4.3 SCHMITT TRIGGER CIRCUITS
4.3.1 Apparatus required:
S.No Equipment/Component name Specifications/Value Quantity
1 IC 741 Refer data sheet 1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 1
3 Multimeter 1
4 Resistors 10K Ω
56 K Ω
2
1
5 Dual Regulated power supply (0 -30V), 1A 1
6` Function Generator (0-2) MHz 1
4.3.2 Theory:
Circuit shows an inverting comparator with positive feedback. This circuit converts an
irregular shaped waveform to square wave or pulse. This circuit is known as Schmitt trigger
or Regenerative comparator or Squaring circuit. The input voltage Vin triggers (changes the
state of ) the output Vo every time it exceeds certain voltage levels called Upper threshold
voltage, VUT and Lower threshold voltage, VLT. The hysteresis width is the difference
between these two threshold voltages i.e. VUT – VLT. These threshold voltages are calculated
as follows.
VUT = (R2/R1+R2) Vsat when Vo= Vsat
VLT = (R2/R1+R2) (-Vsat) when Vo= -Vsat
The output of Schmitt trigger is a square wave when the input is sine wave or triangular
wave, where as if the input is a saw tooth wave then the output is a pulse wave.
R=10kΩ
R2 =10kΩ
Vin = 5Vpp
Schmitt trigger circuit using IC 741
Design Equations:
4.3.3 Design Constraints
Minimum Input voltage is 1v and maximum output voltage is 10v.
Biasing voltage is ±12v
Frequency range is 100 Hz up to 10kHz
4.3.4 Experiment:
1. Connect the components / equipment as shown in the circuit diagram.
2. Switch ON the power supply.
3. Apply 5 Vpp and 1KHz input sine wave using function generator.
4. Connect the channel - 1 of CRO at the input terminals and Channel-2 at the output
terminals.
5. Observe the output square waveform corresponding to input sinusoidal signal.
6. Overlap both the input and output waves and note down voltages at positions on sine
wave where output changes its state. These voltages denote the Upper threshold voltage
and the Lower threshold voltage (see EXPECTED WAVEFORMS below).
7. Verify that these practical threshold voltages are almost same as the theoretical
threshold voltages calculated using formulas given in the THEORY section above.
8. Sketch the waveforms by noting down the amplitude and the time period of the input
Vin and the output Vo.
4.3.4 Model output Schmitt trigger input and output Waveforms:
Observation Table
Sl
no.
Theoretical Values Practical Value
1
2
3
4.3.5 Pre Lab Question:
1. Which is type of comparator called Schmitt trigger using IC741?
2. What is the output wave of Schmitt trigger if the input is sine wave?
3. What type of waveform is obtained when triangular or ramp waveforms are applied to
Schmitt trigger circuit?
4.3.6 Post Lab Question:
1. How do you calculate the theoretical values of VUT and VLT in the case of IC741?
2. What is the Hysteresis width?
3. What is the minimum amplitude of the input sine wave in the case of Schmitt trigger
using IC741
Results:
5. OSCILLATORS5.1 OBJECTIVE
1. Design a RC Phase Shift Oscillator for the oscillation frequency f0 =500Hz with peak to
peak voltage 20V with the closed loop gain of 30. Perform the experiment and plot the
waveforms
2. Design a Wein Bridge Oscillator for the oscillation frequency f0 =1 KHz with peak to
peak voltage 20V for the closed loop gain of 3. Perform the experiment and plot the
waveforms
5.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/Value Quantity1 IC 741 Refer data sheet in
appendix1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 13 Resistors 1.5K Ω
15K Ω10 K Ω18 K Ω435K Ω (1M Ω pot)
13111
4 Capacitors 0.1µf 5
5 Dual Regulated power supply (0 -30V), 1A 16 Function Generator (0-2) MHz 17 ASLK PRO Kit 1
5.3 THEORY
5.3.1 RC phase shift oscillator
The feedback network consists of three identical RC sections. Each section produces a phase
shift of 60o Therefore, the net phase shift of the feedback is 180 o The amplifier stage
introduces a phase shift of 180 o Therefore, the total phase shift between the input and output
is 360 o or 0 o. When the circuit is energized, by switching on the supply, the circuit starts
oscillating. The oscillations will be maintained if the loop gain is at least equal to unity.
Feedback fraction of the RC phase shift network
=1/29
The frequency of oscillation
f0=1/2 πRC6.
Circuit diagram
C=0.1µF, R=1.5K, R1=15K, RF=1M pot
DESIGN:
f0=1/2 πRC6
Rf ≥ 29R1
R1 ≥ 10R
Choose C =0.1µF
f0 = 500 Hz
R = 1 = 1
62πf0C 62πx500x0.1x10−6
R = 1.3 KΩ
Choose R = 1.5KΩ
R1≥15KΩ (to prevent loading)
Therefore, R1 = 10R = 15KΩ
Rf = 29R1=29x15KΩ=435KΩ (Use 1MΩpot)
Test Procedure:
1. Design the circuit for f 0=500Hz.calculate R1,R2,and Rf
2. Connect the circuit as shown in the figure with the designed values.
3. Switch on the power supply and observe the waveform.
4. Note down the amplitude and time period.
5. Plot the waveforms on a graph sheet.
5.3.2 Wein Bridge Oscillator
It is commonly used in audio frequency oscillator. The feedback signal is connected in
the input terminal so that the output amplifier is working as a non-inverting amplifier. The
Wien bridge circuit is connected between amplifier input terminal and output terminal. The
bridge has a series R network, in one arm and a parallel RC network in the adjoining arm. In
the remaining two arms of the bridge, resistor R1 and Rf are connected. the phase angle
criterion for oscillation is that the total phase shift around the circuit must be zero. This
condition occurs when bridge is balanced. At resonance frequency of oscillation is exactly the
resonance frequency of balanced Wien bridge and is given by f0 = 1/ (2πfC).assuming that
the resistors are input impedance value and capacitance are equal to the value in the reactive
stage of Wien bridge. At this frequency, the gain required for sustained.
Design
Given, fo = 1KHz;
Assume C = 0.0015µF
fo = 1/(2π RC),
R = 100KΩ
Rf = 2R = 200KΩ
5.3.3 Design Constraints
The loading effect of the amplifier on the feedback network has an effect on the
frequency of oscillations and can cause the oscillator frequency to be up to 25% higher
than calculated. Then the feedback network should be driven from a high impedance
output source and fed into a low impedance load such as a common emitter transistor
amplifier but better still is to use an Operational Amplifier as it satisfies these
conditions perfectly.
The voltage gain of the Wein bridge oscillator circuit must be equal to or greater than
three “Gain = 3″ for oscillations to start.
Due to the open-loop gain limitations of operational amplifiers, frequencies above
1MHz are unachievable without the use of special high frequency op-amps.
Test Procedure:
1. Design the circuit for f 0=1KHz.calculate R and Rf
2. Connect the circuit as shown in the figure with the designed values.
3. Switch on the power supply and observe the waveform.
4. Note down the amplitude and time period.
5. Plot the waveforms on a graph sheet.
Oscillator Amplitude Time Period
RC Phase shift
Wein Bridge Oscillator
5.4 PRE LAB QUESTIONS
1) Give the condition which determines the frequency of oscillation
2) Give the formula to calculate frequency of oscillation for RC and Wein bridge
oscillator.
3) Where do you use IC oscillators?
5.5 POSTLAB QUESTIONS
1. What are the merits and Demerits of RC phase shift oscillator?.
2. Why do we need three RC networks for a phase shift oscillator?
3. Explain the main difference between an amplifier and an oscillator.
6. APPLICATIONS OF IC 555 TIMER
6.1 OBJECTIVE
1. Design a Monostable multivibrator for an ON- time of 11secs, with capacitor value of 1
µF. Conduct the experiment and plot appropriate graphs
2. Design an Astable multivibrator for a frequency of 1KHz with 60% duty cylcle using
555 timer
6.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/Value Quantity
1 IC 555 Timer Refer data sheet in appendix 1
2 Cathode Ray Oscilloscope (0 – 20MHz) 1 1
3 Resistors
330 Ω15K Ω10 M Ω6.8 K Ω1K Ω
11111
4 Capacitors0.1µf
1µf
2
2
5 Regulated power supply (0 -5V), 1A 16 Function Generator (0-2) MHz 1
6.3 THEORY
The 555 Timer is a monolithic timing circuit that can produce accurate and highly
stable time delays or oscillations. The timer basically operates in one of the two modes—
monostable(one-shot) multivibrator or as an as table(free-running) multivibrator. In the
monostable mode, it can produce accurate time delays from microseconds to hours. In the
astable mode, it can produce rectangular waves with a variable duty cycle. Frequently, the
555 is used in astable mode to generate a continuous series of pulses, but you can also use the
555 to make a one-shot or monostable circuit.
Applications of 555 timer in monostable mode include timers, missing pulse detection,
bounce free switches, touch switches, frequency divider, capacitance measurement, pulse
width modulation (PWM) etc.
In astable or free running mode, the 555 can operate as an oscillator. The uses include
LED and lamp flashers, logic clocks, security alarms, pulse generation, tone generation, pulse
position modulation, etc. In the bistable mode, the 555 can operate as a flip-flop and is used
to make bounce-free latched switches, etc.
Pin diagram of IC55
Functional block diagram of IC 555
6.3.1 MONOSTABLE MULTIVIBRATOR
The circuit has an external resistor and capacitor. The voltage across the capacitor is
used for the threshold to pin 6. When the trigger arrives at pin 2, the circuit produces output
pulse at pin 3. Initially, if the output of the timer is low, that is, the circuit is in a stable state,
transistor Q1 is on and the external capacitor C is shorted to ground. Upon application of a
negative trigger pulse to pin 2, transistor Q1 is turned off, which releases the short circuit
across the capacitor and as a result, the output becomes high. The capacitor now starts
charging up towards vcc through RA. When the voltage across the capacitor equals 2/3vcc
the output of comparator 1 switches from low to high, which in turn makes the output low via
the output of the flip-flop. Also, the output of the flip-flop turns transistor Q1 on and hence
the capacitor rapidly discharges through the transistor. The output of the monostable
multivibrator remains low until a trigger pulse is again applied. The cycle then repeats. Below
figure shows the trigger input, output voltage, and capacitor voltage waveforms. As shown,
the pulse width of the trigger input must be smaller than the expected pulse width of the
output waveform. Moreover, the trigger pulse must be a negative-going input signal with an
amplitude larger than 1/3 vcc. The time for which the output remains high is given by time
period = 1.1RAC
Where RA is in ohms, C in farads and time period in seconds. Once the circuit is triggered, the
output will remain high for the time interval time period. It will not change even if an input
trigger is applied during this time interval. In other words, the circuit is said to be non-
retriggerable. However, the timing can be interrupted by the application of a negative signal
at the reset input on pin 4. A voltage level going from +vcc to ground at the reset input will
cause the timer to immediately switch back to its stable state with the output low.
The trigger input may be driven by the output of astable multivibrator with high duty
cycle. If the desired pulse width is of the order of seconds, the output can be seen using a
LED and the resistance value used will be of the order of MΩ. In this case the trigger can be
supplied manually by grounding the trigger input for a fraction of a second.
Input and output waveform
DESIGN Time period of
pulse=T=1.1RC=11s
Let C=100f
T=1.1RC
11s=1.1*R*1uf
R=10M
6.3.2 ASTABLE MULTIVIBRATOR
An astable multivibrator is a wave-generating circuit in which neither of the output
levels is stable. The output keeps on switching between the two unstable states and is a
periodic, rectangular waveform. The circuit is therefore known as an ‘astable multivibrator’.
Also, no external trigger is required to change the state of the output, hence it is also called
‘free-running multivibrator’. The time for which the output remains in one particular state is
determined by the two resistors and a capacitor externally connected to the 555 timer.
If the output is high initially, capacitor C starts charging towards vcc through RA and
RB. As soon as the voltage across the capacitor becomes equal to 2/3 vcc, the upper
comparator triggers the flip-flop, and the output becomes low. The capacitor now starts
discharging through RB and transistor Q1. When the voltage across the capacitor becomes
1/3vcc, the output of the lower comparator triggers the flip-flop, and the output becomes
high. The cycle then repeats.
The output voltage and capacitor voltage waveforms are shown in Figure below.
Output voltage waveform
the time during which the capacitor charges from 1/3vcc to 2/3 vcc is equal to the time the
output is high and is given by
ton =0.69(RA + RB)C
the time during which the capacitor discharges from 2/3vcc to 1/3vcc is equal to the time the
output is low and is given by
toff =0.69RBC
the total period of the output wave form is
T=ton+toff=0.69(RA+2RB)C
Thus the frequency of oscillation is
fo=1/T=(1.45/(RA+2RB)C)
6.3.3 Design Constraints
The 555 Timer is a very versatile low cost timing IC that can produce a very accurate
timing periods with good stability of around 1%
Duty cycle should be greater than 50% to 80%
Single RC network connected to a single positive supply of between 4.5 and 16 volts.
Load resistance minimum value is 1KΩ
6.4 PRE-LAB
Choose the correct answer
1. A quasi-stable state is such that the output
a) does not change at all
b) Changes unpredictably
c) Changes after a predetermined period of time
d) Changes just after a very short duration of time.
2. A monostable multivibrator is also called a ‘one-shot multivibrator’ because
a) Each time a trigger pulse is applied, the circuit produces a single pulse.
b) The circuit has to be triggered only once
c) The output pulse duration is very small
d) None of the above.
3. true/false
Pin 5 is bypassed to ground through a 0.01 μF capacitor to prevent problems due to random
electrical noise. (True / False)
6.5 EXPRIMENT
6.5.1 MONOSTABLE MULTIVIBRATOR
1. Connect the circuit as shown in the figure with the designed values.
2. Switch on the power supply.
3. Give the trigger pulse to pin 2 just by touching the pin for second.
4. Trigger can be obtained from either CRO external 2v or FG.
5. Check the response by LED glowing upto the designed RC time delay.
6.5.2 ASTABLE MULTIVIBRATOR
1. Connect the circuit as shown in the figure with the designed values.
2. Switch on the power supply and observe the waveform.
3. Note down the amplitude and time period.
4. Plot the waveforms on a graph sheet.
Theoretical O/P Practical O/P
TOTAL TIME TOTAL TIME
TON TON
TOFF TOFF
AMPLITUDE of
Square .Close to VCC
AMPLITUDE of
Square .
Charg& Discharging
Of Capcitor by
measuring Amplitude
2/3 VCC – 1/3 VCC
3.3 – 1.6 = 1.7 v
Charg& Discharging
Of Capcitor by
measuring Amplitude
6.6 POST LAB QUESTION
1. If the diode is connected across RB in the astable multivibrator circuit, what is condition
on RA and RB to achieve duty cycle of 50%?
2. What is the output state of a 555 timer connected in a monostable mode with a high
trigger input.
3. For the proper functioning of a monostable multivibrator, what must be the relative
magnitude of the pulse-width of the trigger input in comparison to the expected pulse-
width of the output waveform?
7. DIGITAL-TO-ANALOG CONVERTER
7.1 OBJECTIVES
1. Design a D to A Convertor with a resolution of 0.3125V using R-2R network.
Assume the logic 1 to be 5V and logic 0 to be 0V.
2. Design a D to A Convertor with a resolution of 0.3125V using binary weighted
resistors. Assume the logic 1 to be 5V and logic 0 to be 0V.
7.2 HARDWARE REQUIRED
S.No Equipment/Component name Specifications/Value Quantity
1 IC 741 Refer data sheet in
appendix
1
3 Resistors 4K Ω
2K Ω
1K Ω
1
7
4
5 Dual Regulated power supply (0 -30V), 1A 1
5 Regulated power supply (0 -5V), 1A 1
6 Multimeter 1
7.3 THEORY
In electronics, a digital-to- analog converter (DAC or D-to-A) is a device for converting a
digital (usually binary) code to an analog signal (current, voltage or electric charge). Digital-
to-analog converters are the interface between the abstract digital world and the analog real
life. An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic circuit
that converts continuous signals to discrete digital numbers. Most of the real world physical
quantities such as voltage, current, temperature, pressure and time are available in analog
form. Even though an analog signal represent a real physical parameter with accuracy, it is
difficult to process, store or transmit the analog signal without introducing considerable error
because of the superimposition of noise as in the case of amplitude modulation. Therefore,
for processing, transmission and storage purposes, it is often convenient to express these
variable in digital form. It gives better accuracy and reduces noise.
D/A conversion is an important interface process for converting digital signals to
analog (linear) signals. An example is a voice signal that is digitized for storage processing,
or transmission and must be changed back into an approximation of the original audio signal
in order to drive a speaker.
Figure-1: A basic DAC
D/A Conversion fundamentals
The DAC fundamentally converts finite-precision numbers (usually fixed-point binary
numbers) into a physical quantity, usually an electrical voltage. Normally the output voltage
is a linear function of the input number.
Figure-2: Block Schematic of a basic DAC
Figure-2 shows the basic configuration for digital-to-analog (D/A) conversion. The
input is an n-bit binary word D and is combined with a reference voltage VR to give an
analog output signal. The output of a DAC can be either a voltage or current. For a voltage
output DAC, the D/A converter is mathematically described as
Vo = K VFS (d12-1+ d22-2+….+dn2-n)
Where, Vo = output voltage
VFS = full scale output voltage
K = scaling factor usually adjusted to unity
d1 d2... dn = n-bit binary fractional word with the decimal point located at the left d1 = most significant bit (MSB) with a weight of VFS / 2
dn = least significant bit (ISB) with a weight of VFs / 2n
Since the input to the D/A converter has a finite number of digital combinations, the resulting
analog output also has a limited number of possible values (unlike pure analog signals, which
may have an infinite number of values). The greater the number of possible values, the closer
the analog output will be to the ideal value. The number of possible levels is determined by
the number of lines or bits in the digital number. More specifically, the number of states is
computed as 2N where N is the number of bits in the digital number. For example, an 8-bit
D/A converter could be expected to produce 28, or 256, discrete output steps. If the full-scale
range of the converter is 0 to 10 volts, then each step will be 10/256, or about 39 millivolts. If
finer resolution is required, we need more bits in the digital number. Thus, a converter with
10-bit resolution would provide 210, or 1024, steps with each step being equivalent to
10/1024, or about 9.8 millivolts. Accuracy of a D/A converter describes the amount of error
between the actual output of the converter and the theoretical output for a given input
number. This rating inherently includes several other sources of error.
A certain amount of time is required for the output of a D/A converter to be correct
once a particular digital number has been applied at the input. Two major factors cause this
delay. First, it takes time for the changes to pass through the converter circuitry; this is called
propagation time. Second, the output of the D/A converter has a maximum rate of change
called slew rate, which is identical to the slew rate problems discussed with reference to op
amps. The delays caused by slew rate limiting and propagation time are collectively referred
to as settling time--the total time required for the analog output to stabilize after a new digital
number has been applied to the input.
The overall operating range of a D/A converter can be shifted up or down from the
optimum point. This DC offset is called offset error. In a somewhat similar manner, one end
of the range can be correct but the other extreme too high or too low. This is called a gain
error or scaling error.
As with A/D converters, we normally want a monotonic output. In other words, the
output should increase whenever the input number increases. However, it is possible for a
D/A converter to have a reduction in analog output at a particular point in its range, even
though the digital input is increasing uniformly.
Figure-3: Oscilloscope display showing several imperfections in a low-quality D/A converter.
Figure-3 shows the performance of a low-quality D/A converter. Several of the potential
problems described are present in the converted waveform. The input to the converter is a 4-bit
down counter (e.g., 15, 14, 13... 2, 1, 0, 15), and the analog output should be 16 equally spaced,
decreasing steps for each cycle, producing a reverse saw tooth waveform. If you examine the
waveform carefully, you can see the 16 distinct output levels; however, the steps are not equal in
amplitude (linearity problems)--the midpoint level actually increases instead of decreasing (non
monotonic), and there are several glitches caused by switching transients.
WEIGHTED D/A CONVERTER
Figure- 4 shows the schematic diagram of a weighted digital-to-analog converter circuit built
around a 741 op amp. You can recognize the configuration as being identical to the inverting
summing amplifier.
Figure-4: A weighted D/A converter with 3-bit resolution
Calculations: Output Voltage is given by
Vo = - ((Rf / R1)+ (Rf / R1) +(Rf / R1) ) VR
where, VR = 5V , Rf = 2R , b3 (MSB bit ) andb0(LSB bit )
R2R LADDER D/A CONVERTER
One of the most popular methods for D/A conversion is shown in Figure-5. It is called
an R2R ladder D/A converter, since the input network resembles the rungs on a ladder and
the resistors in the input network are either equal (R) or have a 2:1 ratio (2R). One advantage
of the R2R converter over the weighted converter previously discussed is immediately
apparent; the resistors have a 2:1 ratio regardless of the number of bits being converted. This
makes matching resistors much easier and even makes the use of integrated resistors
practical.
An easy way to analyze the operation of the circuit is to Thevenize the input circuit
for one or more digital input numbers. Once the input circuit has been simplified with The
venin’s Theorem, you will be left with a simple inverting amplifier circuit whose input
voltage is the The venin equivalent voltage and whose gain is determined by the ratio of
feedback resistance to The venin equivalent input resistance. By performing several analyses
with different input numbers, you will discover that the least significant input (b0) produces
the least effect on output voltage, and the next input (bl) has twice as much effect on output
voltage. Similarly, bit b2 has twice the effect of b1, but only half the effect onoutput voltage
of b3. These variable effects are identical to the relative weights of the digits in a binary
number.
Figure-5: A 3-bit R2R ladder D/A converter utilizing a 741 op amp
Calculations: Output Voltage is given by
Vo = - VR * (Rf / 2R) * ( b2/2 + b1/4 + b0/8 )
where, VR = 5V , Rf = 2R , b2(MSB bit ) and b0 (LSB bit )
Design Constraints
Resistance should be use ±1 to ±5 tolerance
Input voltage should be 5V for high and 0V for low.
EXPERIMENT
(a) Weighted Resistor DAC
1. Setup the circuit as shown in Figure-4.
2. Reference voltage VR is set as 5V
3. Find the output voltage Vo for different combinations of digital binary inputs from
000 to 111.
4. Compare the calculated values with observed values and plot DAC characteristics
(b) R-2R LADDER DAC
1. Setup the circuit as shown in Figure-5. Select the approximate value of R and 2R
2. Set the approximate value of R and 2R.
3. Reference voltage VR is set as 5V
4. Find the output voltage Vo for different combinations of digital binary inputs from
000 to 111.
5. Compare the calculated values with observed values and plot DAC characteristics
(c) Experimental data and observations
Weighted Resistor DAC
b2 b1 b0 Vo ( observed) Vo ( Calculated)
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
R-2R LADDER DAC
b2 b1 b0 Vo ( observed) Vo ( Calculated)
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 0 1
1 1 0
1 1 1
PRE LAB QUESTIONS
1. Classify DACs on the basis of their output.
2. How many resistors are required in a 12-bit weighted-resistor DAC?
3. How many levels are possible in a 2-bit DAC? What is its resolution if the output voltage
range is 0 to 3 V?
4. A 5-bit D/A converter is available. Assume that ‘00000’ corresponds to an output of +10 V
and that the D/A converter is connected for -0.1V per increment. What output voltage will be
produced for ‘11111’?
POST LAB QUESTIONS
1. Determine the output voltage of the DAC in Figure-7(a). The sequence of four-digit binary codes
represented by the waveforms in Figure-7(b) are applied to the inputs. A high level is a binary l,
and low level is a binary 0. The least significant binary digit is Do.
Figure-7
2. The R-2R ladder DAC shown in Figure-8 below consists of 10K & 20KΩ resistors, VREF =
2V and R1 = 10KΩ. Determine the values required for RF such that VFS = 10V.
Figure-8
8. AC AMPLIFIERS8.1 OBJECTIVE
To sketch the following basic op-amp circuits and explains the operation of each:
Inverting amplifier
Non-inverting amplifier
8.2 SOFTWARE REQUIRED
ORCAD 9.2
8.3 THEORY
8.3.1 AC AMPLIFIER
The inverting and non-inverting op-amp amplifier configurations respond to both ac and dc
signals. To get the ac frequency response of an op amp or if the ac input signal is
superimposed with dc level, it becomes essential to block the dc component. This is achieved
by using an AC amplifier with a coupling capacitor. AC amplifiers are of inverting and non-
inverting type.
8.3.2 INVERTING AC AMPLIFIER
The circuit is shown in below figure. The capacitor blocks the dc component of the input and
together with the resistor R1 sets the lower 3 dB frequency of the amplifier.
8.3.3. NON-INVERTING AMPLIFIER
In most cases it is possible to DC couple the circuit. However in this case it is necessary to
ensure that the non-inverting has a DC path to earth for the very small input current that is
needed. This can be achieved by inserting a high value resistor, R3 in the diagram, to ground
as shown below. The value of this may typically be 100 k ohms or more. If this resistor is not
inserted the output of the operational amplifier will be driven into one of the voltage rails.
When inserting a resistor in this manner it should be remembered that the capacitor-resistor
combination forms a high pass filter with a cut-off frequency. The cut-off point occurs at a
frequency where the capacitive reactance is equal to the resistance.
Inverting Amplifier
Design an inverting amplifier for the gain of 15. Let R1=1.5k, C=0.1µF.
Non-Inverting amplifier
Design a non-inverting amplifier for the gain of 15. Let R1=1.5k , C=0.1µF.
TEST PROCEDURE
1. Open the Pspice AD Lite software by double clicking its icon.
2. After few moments Command window will appear.
3. Go to the File Menu and select a new text file. (File New text file)
4. A blank text file will appear with a title ‘untitled’
5. Now start typing your program. After completing, save the text file as .cir with
appropriate name. To execute the program go to Debug Menu and select Run.
6. After execution output will appear in the Command window .If there is an error then
with an alarm, type of error will appear .
7. If the results contain errors, start up the text editing program again and modify the
net list.
8. Rectify the error if any and go to Debug Menu and select Run.
9. If there is no errors go to Trace menu and click add trace. Enter the output node
Voltage and click ok then the output will display.
Prelab
1. What is the input impedance of a non inverting op-amp amplifier?
2. If the open loop gain of an op-amp is very large, does the closed loop gain depend upon
the external components or the op-amp?
3. Define common mode rejection ratio
4. Explain the meaning of open loop and closed loop operation of an op- amp?
5. What is a practical op-amp? Draw its equivalent circuit.
Postlab
1. Determine the bandwidth of a non-inverting amplifier, voltage follower and inverting
amplifier
2. Determine the gain-bandwidth product of each amplifier.
3. Determine the input and output impedances of each amplifier.
9. OP-AMP APPLICATIONS9.1 OBJECTIVE
To study the operation of following circuits
a)Adder
b)Clipper
c)Clamper
d)Square waveform generator
9.2 SOFTWARE REQUIRED
ORCAD 9.2
9.3 THEORY
9.3.1 Summing amplifier
The summing amplifier is an application of the inverting op-amp configuration. The
summing amplifier has two or more inputs, and its output age is proportional to the algebraic
sum of its input voltages. Fig. 7-4 shows a two-input inverting summing amplifier.
Case-1: If all the three resistors are equal (R1=R2=Rf=R) then
VO = - (Vinl + Vin2)
The above equation shows that the output voltage has the same magnitude as the sum of two
input voltages but with a negative sign indicating inversion.
Case-2: When Rf is larger than the input resistors, the amplifier has a gain of −
R f
R
where R is the value of each equal value input resistor (R1=R2=R). The general expression for the
output is
Vo=−R f
R(V in 1+V in 2 )
The above equation shows that the output voltage has the same magnitude as the sum of all the
input voltages multiplied by a constant determined by the ratio −
R f
R
Case-3: By setting the ration Rf/R equal to the reciprocal of the number of inputs (n), ie.,
Fig 1.Summing Amplifier
Fig 2.Summer output
R f
R=1
n, a
summing amplifier can be made to produce the mathematical average of the input voltages.
Case-4: A different weight can be assigned to each input of a summing amplifier by simply
adjusting the values of the input resistors. In this case, the output voltage can be expressed as
Vo=−(Rf
R1V in1+
R f
R2V in2 )
The weight of a particular input is set by the ratio of Rf to Rx for the input (Rx= R1, R2…)
1.3.2. Active clipper
Clipper is a circuit that is used to clip off (remove) a certain portion of the input
signal to obtain a desired output wave shape. In op-amp clipper circuits, a rectified diode ma
be used to clip off certain parts of the input signal. Fig. 2-2-4 (a) shows an active positive
clipper, a circuit that removes positive parts of the input signal. The clipping level is
determined by the reference voltage
Vref.R
Vo
2.2k
Vin D1
-
uA741
+
Vref
.
+VCC 10k
POT
Fig 3(a) Active Limiter
(b) (c)
Fig 4 (b) input & output waveforms with +Vref, (c) input & output waveforms with -Vref
With the wiper all the way to the left, Vref is o and the non-inverting input is grounded.
When Vin goes positive, the error voltage drives the op-amp output negative and turns on the
diode. This means the final output VO is 0 (same as Vref) for any positive value of Vin.
When Vin goes negative, the op-amp output is positive, which turns off the diode
and opens the loop. When this happens, the final output VO is free to follow the negative
half cycle of the input voltage. This is why the negative half cycle appears at the output. To
change the clipping level, all we do is adjust Vref as needed.
Active clamper
In clamper circuits, a predetermined dc level is added to the input voltage. In other
words, the output is clamped to a desired dc level. If the clamped dc level is positive, the
clamper is called a positive clamper. On the other hand, if the clamped dc level is negative, it
is called a negative clamper. The other equivalent terms for clamper are dc inserter or dc
restorer.
A clamper circuit with a variable dc level is shown in fig (a). Here the input wave
form is clamped at +Vref and hence the circuit is called a positive clamper.
1uF
C1
- + Vo
Vp RL
Vin 1k
R
4.7k +VCC D1
-
uA741
+
Rp -VCC
10k
Fig 5 (a) Peak clamper circuit
The output voltage of the clamper is a net result of ac and dc input voltages applied to the
inverting and non-inverting input terminals respectively. Therefore, to understand the circuit
operation, each input must be considered separately. First, consider Vref at the non-inverting
input. Since this voltage is positive, is +Vo is positive, which forward biases diode D1. This
closes the feedback loop and the op-amp operates as a voltage follower. This is possible
because C1 is an open circuit for dc voltage. Therefore Vo = Vref. As for as voltage Vin at the
inverting input is concerned during its negative half-cycle D1 conducts, charging C1 to the
negative peak value of the VP. However, during the positive half-cycle of Vin diode D1 is
reverse biased and hence the voltage VP across the capacitor acquired during the negative
half-cycle is retained. Since this voltage VP is in series with the positive peak voltage VP, the
output peak voltage Vo=2VP. Thus the net output is Vref +VP, so the negative peak of 2VP is
at Vref. For precision clamping C1Rd<<T/2, where Rd is the forward resistance of the diode
D1 (100Ω typically) and T is the time period of Vin. The input and output wave forms are
shown in figure.
(i) (ii)
(iii)
Fig 6(b) Input and output waveforms (i) with Vref=0V, (ii) with +Vref, (iii) with -Vref
Resistor R is used to protect the op-amp against excessive discharge currents from capacitor
C1 especially when the dc supply voltages are switched off. Negative clamping at a negative
voltage is accomplished by reversing diode D1 and using the negative reference voltage –
Vref.
Square wave generator
The square wave generator circuit is forced to operate in the saturated region. That is,
the o/p of the Op-Amp is forced to swing between positive saturation (+V sat) and negative
saturation (-Vsat), resulting in the square wave output. This square wave generator is also
called free running or astable multivibrator.
R2/[R1+R2]Vout = βVout
Fig.7 square wave generator
A fraction of the output (βV) is feedback to the input non-inverting terminal. Thus
the Vref is βV and may take values as + βVsat or – βVsat. The output is also feedback to the
negative i/p terminal after integrating by means of a low pass RC combination. Whenever
the i/p at the negative terminal exceeds Vref switching takes place resulting in a square wave
output. Time period of square wave is given as
for R1 = 1.16 R2, it can be seen that T = 2RC.
Square Wave Generator
T = 1.6 ms
V = 24 V
Vsat = 12V; βVsat = 4v
EXPERIMENT
Use op-amp dc power supply voltages of + 15V.
(1) Summer
Connect the summer circuit as shown in fig 1 with R1, R2, Rf = 10KΩ. Use PSPICE
simulation
(2) Active clipper
Connect the clipping circuit as shown in fig 3 (a) with R=2.2kΩ. Use 1N4002 diode.
Sinusoidal input of amplitude 3Vp and frequency 1KHz using PSPICE simulation.
(3) Active clamper
Design a positive clamping circuit with clamping level at zero as shown in fig.5 (a). Note that
Vref = 0V. Consider C1 = 0.1µF, R = 4.7 KΩ and RL = 10 KΩ . Use 1N4002 diode. Feed
5VPP, 10 KHz sinusoidal inputs. Simulate using PSPICE.
(4)Square waveform generator
Connect the circuit as shown in fig 7 with C=0.05µf, R1=20K pot, R2=10K, Rf=10K.
Simulate using PSPICE
Prelab
1. What is a Differential amplifier
2. Define a Summing amplifier
3. Define difference mode gain and common mode gain
4. Give the applications of summing and differential amplifier
5. What is the total time period of the waveform generated by the square wave generator?
6. How can you obtain a non symmetrical square waveform?
7. Which circuit is called a gating circuit? Why?
8. A triangular wave can be generated by a integrating ___________.
9. What is the difference between saw tooth and triangular wave?
TEST PROCEDURE
1. Open the Pspice AD Lite software by double clicking its icon.
2. After few moments Command window will appear.
3. Go to the File Menu and select a new text file. (File Newtext file)
4. A blank text file will appear with a title ‘untitled’
5. Now start typing your program. After completing, save the text file as .cir with
appropriate name. To execute the program go to Debug Menu and select Run.
6. After execution output will appear in the Command window. If there is an error then
with an alarm, type of error will appear.
7. If the results contain errors, start up the text editing program again and modify the net
list.
8. Rectify the error if any and go to Debug Menu and select Run.
9. If there is no errors go to Trace menu and click add trace. Enter the output node voltage
and click ok then the output will display.
Postlab
1. If the diode is reversed in fig. 3 (a), what would the output be like?
2. If the diode is reversed in fig. 5(a), what would be the output?
10. ACTIVE FILTERS
10.1 OBJECTIVE
To construct a low pass , high pass ,Band pass and Band stop filter using PSPICE simulation
and to plot the frequency response.
10.2 SOFTWARE REQUIRED
ORCAD 9.2
10.3 THEORY
A filter is a circuit that lets certain frequencies pass and blocks other frequencies. This
selective nature can be done two ways, either with passive filters or with active filters.
Passive filters completely comprised of passive elements; namely resistors, capacitors and/or
inductors. Active filters use active devices, i.e. an op-amp, to filter out unwanted signals.
Active filters have the following advantages over passive filters.
Gain and frequency adjustment and tuning.
No inductors (reduces cost and size).
No loading effects.
Some disadvantages of active filters.
Bandwidth limitations
Fabrication tolerances
Can only respond to a specific range of signal magnitudes.
Figure 2 shows the performance of an ideal low-pass, band-pass, and high pass circuit. Active
filters can be classified as; low-pass, high-pass, band-pass, notch, or all pass circuit. These
circuits are all used for different purposes, but this lab will focus on the design of second
order low pass and high pass Filters using PSPICE.
10.1.Graph of practical (a) low pass and (b) high pass filter (c) Band Pass filter
(d) Band Stop filter
SECOND ORDER LOW PASS FILTER
Fig.10.2.Second-Order low-pass filter
SECOND ORDER HIGH PASS FILTER
Fig.10.3.Second-Order high-pass filter
BAND PASS FILTER
The bandpass filter passes one set of frequencies while rejecting all others. The band-stop
filter does just the opposite. It rejects a band of frequencies, while passing all others. This is
also called a band-reject or band-elimination filter. Like bandpass filters, band-stop filters
may also be classified as (i) wide-band and (ii) narrow band reject filters.
The narrow band reject filter is also called a notch filter. Because of its higher Q, which
exceeds 10, the bandwidth of the narrow band reject filter is much smaller than that of a wide
band reject filter.
Band Pass Filter
Fig 10.4 Band Pass Fiter
This cascading together of the individual low and high pass passive filters produces a low
“Q-factor” type filter circuit which has a wide pass band. The first stage of the filter will be
the high pass stage that uses the capacitor to block any DC biasing from the source. This
design has the advantage of producing a relatively flat asymmetrical pass band frequency
response with one half representing the low pass response and the other half representing
high pass response as shown.
The higher corner point ( ƒH ) as well as the lower corner frequency cut-off point ( ƒL ) are
calculated the same as before in the standard first-order low and high pass filter circuits.
Obviously, a reasonable separation is required between the two cut-off points to prevent any
interaction between the low pass and high pass stages. The amplifier also provides isolation
between the two stages and defines the overall voltage gain of the circuit.
The bandwidth of the filter is therefore the difference between these upper and lower -3dB
points. For example, if the -3dB cut-off points are at 200Hz and 600Hz then the bandwidth of
the filter would be given as: Bandwidth (BW) = 600 – 200 = 400Hz. The normalized
frequency response and phase shift for an active band pass filter will be as follows.
While the above passive tuned filter circuit will work as a band pass filter, the pass band
(bandwidth) can be quite wide and this may be a problem if we want to isolate a small band
of frequencies. Active band pass filter can also be made using inverting operational amplifier.
So by rearranging the positions of the resistors and capacitors within the filter we can
produce a much better filter circuit as shown below. For an active band pass filter, the lower
cut-off -3dB point is given by ƒC2 while the upper cut-off -3dB point is given by ƒC1.
BAND-STOP (OR REJECT) FILTER.
Fig 10.5 Band Stop Filter
A wide band-stop filter using a low-pass filter, a high-pass filter and a summing amplifier
is shown in figure. For a proper band reject response, the low cut-off frequency fL of high-
pass filter must be larger than the high cut-off frequency fH of the low-pass filter. In addition,
the pass band gain of both the high-pass and low-pass sections must be equal.
This is also called a notch filter. It is commonly used for attenuation of a single frequency
such as 60 Hz power line frequency hum. The most widely used notch filter is the twin-T
network illustrated in fig. (a). This is a passive filter composed of two T-shaped networks.
One T-network is made up of two resistors and a capacitor, while the other is made of two
capacitors and a resistor. One drawback of above notch filter (passive twin-T network) is that
it has relatively low figure of merit Q. However, Q of the network can be increased
significantly if it is used with the voltage follower. Here the output of the voltage follower is
supplied back to the junction of R/2 and 2 C.
10.4 PRE-LAB
1. Compute the transfer function of the amplifier in Figure assuming an ideal op-amp.
Use the PSPICE model of an op-amp and verify your results in PSPICE using the following
values: Vcc=+12V, Vee=-12V, R1=1kΩ, and VS being a sin wave with a frequency of 10
kHz and amplitude of 1mV.
10.5 EXPERIMENT
10.5.1 Low pass filter
Design a Second order low pass filter as shown in figure 2 for the values R1 = R2=3.3KΩ,
C2=C4=0.047uF, Rx=5.8KΩ, Ry-10KΩ and sinusoidal input of amplitude 1V and frequency
10KHz using PSPICE simulation.
10.5.2 High pass filter
Design a Second order High pass filter as shown in figure 3 for the values R1 = R2=3.3KΩ,
C2=C4=0.047uF, Rx=5.8KΩ, Ry=10KΩ and sinusoidal input of amplitude 1V and frequency
10KHz using PSPICE simulation.
10.5.3 Band Pass Filter
Design a Band Pass Filter as shown in figure 4 keep the same values of low pass and high
pass filter values and sinusoidal input of amplitude 1V and frequency 10KHz using PSPICE
simulation.
10.5.4 Band Stop Filter
Design a Band Stop filter as shown in figure 5 for the corresponding values as in figure and
sinusoidal input of amplitude 1V and frequency 10KHz using PSPICE simulation.
10.6 TEST PROCEDURE
1. Open the Pspice AD Lite software by double clicking its icon.
2. After few moments Command window will appear.
4. Go to the File Menu and select a New text file. (File Newtext file)
5. A blank text file will appear with a title ‘untitled’
6. Now start typing your program. After completing, save the text file as .cir with
appropriate name. To execute the program go to Debug Menu and select Run.
7. After execution output will appear in the Command window. If there is an error then with
an alarm, type of error will appear.
8. If the results contain errors, start up the text editing program again and modify the net list.
9. Rectify the error if any and go to Debug Menu and select Run.
10. If there is no errors go to Trace menu and click add trace. Enter the output node voltage
and click ok then the output will display.
10.7 POST LAB QUESTION
1. Derive the transfer function of the circuit in Figure. By observing the transfer function,
what is the purpose of this topology? Verify your results in PSPICE with an “AC”
simulation using R1=500 Ω, R2=2.5kΩ, a source with a 0.5V magnitude, and C=0.01F.
Do the PSPICE results agree with what you derived?