Linear Integrated Circuits notes.doc

Linear Integrated Circuits

Chapter 1:- Operational Amplifier (Op-Amp) Marks: - 10

Importance of Op-Amp:-o Block diagram of Op-Amp and function of each block. o The circuit such as balanced, Unbalanced, differential amplifiers with simple current source,

level shifter and complementary push-pull amplifier. o Equivalent Circuit, Circuit Symbols and Terminals. o Op-Amp IC-741 pin diagram and function.

Parameters of Op-Amp:-a. Input offset voltage.b. Input offset current. c. Input bias current.d. Differential input resistance, e. Input capacitance, f. Input voltage range, g. Offset voltage adjustment range, h. Common Mode Rejection Ratio (CMRR), i. Supply Voltage Rejection Ratio (SVRR), j. Large signal voltage gain.k. Transfer characteristics,l. Supply voltages, m. Supply current, n. Output voltage swing, o. Output resistance, p. Slew rate, q. Gain bandwidth product, r. Output short circuit current.

Prepared by: - Sudershan. Dolli V.V.P.Polytechnic, Solapur

Linear Integrated CircuitsThe operational amplifier (Op-Amp):- An operational amplifier (Op-Amp) is a direct coupled high gain amplifier usually consisting of one

or more differential amplifiers. The operational amplifier (Op-Amp) is a versatile device that can be used to DC as well as AC input

signals. It originally designed for performing mathematical operations such as addition, subtraction,

multiplication, integration, differentiation, etc. thus the name “operational amplifier” is designated as “Op-Amp”.

With suitable feedback components, the operational amplifier (Op-Amp) can be used for variety of applications, such as, amplifiers, oscillator, filter, regulators, etc

Block diagram of Op-Amp and function of each block:-

Working:- Input stage:-

o The input stage is dual input-balanced output differential amplifier.o This stage generally provides most of the voltage gain of the amplifier.o This stage also provides high input impedance (2 MΩ).

Intermediate stage:- o The intermediate stage is driven by the output of first stage (input stage), and is dual input-

unbalanced output.o The intermediate stage is usually a differential amplifier.o Because the direct coupling is used, the DC voltage of at the intermediate stage is well above

the ground level. DC level shifter stage (level translator):-

o The DC level shifter stage, is usually a emitter follower circuit which is used after the intermediate stage to shift DC level downwards to zero volts with respect to ground.

Output stage:- o The final stage (output stage) is a complementary symmetry push-pull amplifier.o The output stage increases output voltage swing, and supplies current supplying capability of

Op-Amp.o Output stage provides low output impedance (75 Ω).


Linear Integrated CircuitsEquivalent circuits of each stages of Op-Amp:-

Dual input-balanced input differential amplifier (Input stage):-

o The input stage is dual input-balanced output differential amplifier with constant current source.o This stage generally provides most of the voltage gain of the amplifier.o This stage also provides high input impedance (2 MΩ).o Differential amplifier is a two input transistor amplifier which amplifies the difference between

the two input signals Vin1 and Vin2. o The circuit is in the form of bridge and is excited by +VCC and –VEE and output Vo= VC1 –

VC2 o When supply voltages are applied then Q1 and Q2 turns ON. o As the circuit is symmetrical

Therefore IB1= IB2, and IC1= IC2 o By applying KVL at the output, we get,

VC1= VCC- IC1 RC1 VC2= VCC- IC2 RC2

o As, IC1= IC2, RC1= RC2, therefore, VO= 0

o As the output is taken between two collectors, the zero output is obtained, and the circuit is said to be balanced.

Dual input-unbalanced output (Intermediate stage):-


Linear Integrated Circuitso The intermediate stage is driven by the output of first stage (input stage), and is dual input-

unbalanced output.o The intermediate stage is usually a dual input-unbalanced output differential amplifier.o Because the direct coupling is used, the DC voltage of at the intermediate stage is well above the

ground level.o In this amplifier the output is measured at collector of only one of the two transistors with

respect to ground.o In the quiescent condition some DC voltage exists at the output terminals.o This is why the amplifier is unbalanced output type differential amplifier.o This unbalanced DC voltage present at the output acts as the error voltage in the desired output.

Level shifter stage:-

o Due to direct coupling between the first two stages, the input at level shifter stage contains dc signal along with the required ac output.

o This increase in DC level tends to shift the operating point of the succeeding stage which distorts the waveform.

o To avoid saturation of o/p voltage, the DC level shifter stage, usually a emitter follower circuit, is used after the intermediate stage to shift DC level downwards to zero volts with respect to ground.

o So that highest amplitude ac signal can be amplified without getting saturated. o The simplest level shifter circuit is a emitter follower with a voltage divider

Question: - Explain how offset voltage nulling is an important in Op-Amp and why it is required in op- amp application? Answer:-



The 741 type Op-Amp has a feature of offset voltage nulling capability. The 741 type Op-Amp has pin number 1 and 5 for this purpose. As shown in figure, a 10 KΩ potentiometer be placed across offset null pins 1 and 5 and a wiper be

connected to the negative supply pin 4. By varying the position of the wiper on the 10kΩ potentiometer, we are trying to remove the

mismatch between inverting and non- inverting input terminals of the op- amp. Adjust the wiper until the output offset voltage is reduced to zero.

Equivalent circuit of the Op-Amp (non-ideal Op-Amp):-

The fig shows the equivalent circuit of a practical OP- AMP. It includes important values such as Av, RI, and RO etc. Note that Av Vd is the equivalent Thevenin voltage source and Ro is the Thevenin equivalent

resistance looking back into the output of an OP- AMP. The value of input resistance RI is finite here (2 MΩ) and that the output resistance RO is non-zero

(75Ω) because the OP- AMP is non -ideal. As will be discussed later, the parameters Av, RI, and RO are called as the open loop parameters. Vd= ( V1 – V2) is called as differential input voltage and Av is called as the open loop gain. Hence the output voltage is given by,

Vo = Av X Vd = Av (V1 – V2) V1 and V2 are the voltages at the non-inverting and inverting input terminals of the OP- AMP with respect to the ground.

Equation indicates that the OP- AMP responds only the differential input Vd. The open loop voltages gain Av is of very large value. Hence the value of Vd even for maximum

output voltage is extremely small. For example, to obtain

Vo(max)= 10 V a 741 OP-AMP needs Vd = 10 / 2 X 105 = 50μV



Op-Amp parameters:-

Input offset voltage (Vio):- o There is small error or offset voltage at the due to mismatching of components in the Ic’s o This error voltage at output is reduced to zero by applying a suitable amount of dc voltage at the

input terminals called as the input offset voltage. It is always in mv or μv Gain bandwidth product current:-

o The gain bandwidth product is the bandwidth of the Op-Amp when gain is 1. o Although for the 741 Op-Amp it is not listed under electrical characteristics, but from the open

loop voltage gain versus frequency graph it can be found to be approximately 1 MHz. CMRR:-

o CMRR is the ratio of difference mode gain to common mode gain. CMRR= Ad/Ac

o In ideal case common mode gain Ac=0, so CMRR is equal to infinite and practically common mode gain (Ac) has low value, thus CMRR is very high

Slew Rate :- o The slew rate is defined as maximum rate of change of output voltage per unit time.o It is expressed in V/μs o S.R.= dvo/dt o Slew rate indicates that how rapidly the output of op-amp can change in response to change in

input frequency. Input offset current:-

o The algebraic difference between the currents flowing into the inverting and non-inverting terminals of Op-Amp is called an input offset current (Iios).

Iios = l IB1-IB2 lo IB1 is current flowing through non-inverting terminalo IB2 is current flowing through inverting terminalo Ideally input offset current should be zero.o Typically (practically) the input offset current is 6 nano-Amps.

Input bias current:- o Input bias current is the average of the currents flowing into the two input terminals of the Op-

Amp.Input bias current = (IB1+IB2)/2.

o IB1 is current flowing through non-inverting terminalo IB2 is current flowing through inverting terminalo Ideally input bias current should be zero.o Typically (practically) the input bias current is 50 nano-Amps.

Differential input resistance:-


Linear Integrated Circuitso It is defined as the equivalent resistance which can be measured at either at the inverting or non-

inverting terminal with other terminal connected to ground.o Ideally input resistance is infinite.o Typically (practically) the input resistance is 2 MΩ.

Input capacitance:- o It is defined as the equivalent capacitance which can be measured at either at the inverting or

non-inverting terminal with other terminal connected to ground.o Ideally input capacitance must be minimum.o Typically (practically) the input capacitance is 1.4 pF.

Input voltage range:- o When same voltage is applied to both the input terminals, the voltage is called as common mode

voltage VCM. o The input voltage range is the range of common mode voltages over which offset specifications

apply.o For IC 741 the input voltage range is + 13 volts.

Offset voltage adjustment range:- o The offset voltage adjustment range is the range through which the input offset voltage can be

adjusted by varying potentiometer, to make the output offset voltage zero.o For IC 741 offset voltage adjustment range is + 15 mili-volts.

Supply Voltage Rejection Ratio (SVRR):- o The change in an Op-Amps input offset voltage, Vio, cas=used by variations in supply voltages

is called as supply voltage rejection ratio.o SVRR is also referred as power supply rejection ratio (PSRR).

Large signal voltage gain:- o Since the Op-Amp amplifies between the two input terminals, the voltage gain of the amplifier is

defined asVoltage gain = output voltage / differential input voltage.AV=VO / VID

Supply voltages:- o Some Op-Amp needs a dual power supply and some works on single polarity power supply.o The dual power supply is + 15 volts while a single polarity power supply is typically + 12 volts

or +15 volts. Supply current:-

o Supply current, IS, is the current drawn by the Op-Amp from power supply.o For IC 741C Op-Amp the supply current is 2.8 mili-amps.

Output voltage swing:- o The output voltage swing indicates the values of positive and negative saturation voltages of the

Op-Amp. o The output never exceeds these limits for given supply voltages + VCC and –VEE.o For IC 741C output voltage swing is guaranteed between -13 volts and +13 volts.

Output resistance:- o Output resistance, RO, is the equivalent resistance that can be measured between the output

terminal of the Op-Amp and the ground.o It is 75 Ω for IC 741C Op-Amp.

Output short circuit current (I SC):-


Linear Integrated Circuitso If the output terminal of the Op-Amp is connected to ground, the current through the short will

be much higher than IB or Iio.o This high current may damage the Op-Amp it does not have a short circuit protection.o The ISC is 25 mA for IC 741C Op-Amp.

Question: - Write the meaning of following IC number’s:- a) μA 741 T C.b) MC34001 P 0O TO 70O Cc) LM101A F

Answer:-1. IC number: - μA 741 T C (manufactured by Fairchild semiconductors)

μA 741 Device type Op-Amp

T Package type Mini DIP package

C Temperature range Commercial temperature range (0O TO 70O C)

2. IC number: - MC34001 P 0O TO 70O C (manufactured by Motorola)MC34001 Device type Op-Amp

P Package type Plastic DIP package

0O TO 70O C Temperature range Commercial temperature range (0O TO 70O C)

3. IC number: - LM101A F (manufactured by National semiconductors)LM101A Device type and temperature range Op-Amp ;

Temperature range:-In LM101:- 1 denotes a military temperature

range (-55oC to 125oC).In LM201:- 2 denotes a industrial temperature

range (-20oC to 85oC).In LM301:- 3 denotes a commercial temperature range (0O TO 70O C).

F Package type Flat package

Question: - Draw and explain the ideal transfer of Op-Amp.Answer:-



In basic op – amp operation, the offset voltage is assumed to be zero where the output voltage is plotted against input difference voltage (Vid) keeping gain constant.

However, that the output voltage cannot exceed the positive and negative saturation voltage. These saturation voltage are specified by an output voltage swing rating of the op – amp for given

value of supply voltage that means output voltage is directly proportional to the input difference voltage only until it which is the saturation voltage and that there after output voltage remains constant.

Hence, the curve is called an ideal voltage transfer curve.List the ideal values and practical values (typical values) of Op-Amp:-

Parameters Ideal PracticalInput impedance ∞

Voltage gain ∞Bandwidth ∞

CMRR ∞Slew rate 0

SVRR (PSRR) 0Input offset voltage 0Input bias current 0

Input offset current 0Output offset voltage 0

Output impedance 0



Chapter 2:- Operational Amplifier (Op-Amp) configuration Marks: - 18

Open loop and closed loop configuration of Op-Amp: - its comparison. Virtual ground, virtual short concept. Open loop configuration :- Inverting , Non-inverting Close loop configuration :- Inverting, non- inverting, differential amplifier, unity gain amplifier (voltage

follower), inverter(sign changer) Inverting and non-inverting configuration of Adders (summing amplifier, scaling Amplifier, averaging

amplifier), Subtractor. Basic Integrator Basic Differentiator Basic concept of frequency compensation of Op-Amp and offset nulling. Numerical based on designing of above circuit.



Open loop configuration’s of Op-Amp:-1. Differential amplifier.2. Inverting amplifier.3. Non-inverting amplifier.

Differential amplifier:-

o Figure shows the open loop differential amplifier in which input signal V in1 and Vin2 are applied to positive and negative terminals.

o Since Op-Amp amplifies the difference between two input signals, this configuration is called the differential amplifier.

o As OP-Amp can amplify AC as well as DC input signals, this means V in1 and Vin2 can be AC or DC voltages.

o The source resistance Rin1 and Rin2 are normally negligible compared to input resistance Rin of Op-Amp.

o Hence the output voltage (VO), is equal to the voltage gain (AV) times the differential input voltages (Vin1 - Vin2),

VO= AV (Vin1 - Vin2)


Linear Integrated Circuitso The polarity of the output voltage depends on the polarity of the input difference voltage (V in1 -

Vin2).

Open loop inverting amplifier:-

waveform

o Figure shows the open loop inverting amplifier in which only one input signal (V in) is applied and that is to the inverting input terminal.

o The non-inverting input terminal is grounded.o Since V1= 0 volts and V2= Vin; the output voltage will be

VO= -Av X Vin

o The negative sign indicates that the output voltage is out of phase with respect to the input by 180o or is of opposite polarity.

o Thus in the inverting amplifier the input signal is amplified by the gain (AV) and is also inverted at the output.

Open loop non-inverting amplifier:-

waveformo Figure shows the open loop non-inverting amplifier in which only one input signal (V in) is

applied and that is to the non-inverting input terminal.o The inverting input terminal is grounded.o Since V1= Vin volts and V2= 0 ; the output voltage will be


Linear Integrated CircuitsVO= Av X Vin

o The output voltage is in phase with respect to the input by 360o or is of same polarity.o Thus in the non-inverting amplifier the input signal is amplified by the gain (AV) and is also non-

inverted (in phase) at the output.

Question: - Calculate the output voltage for open-loop non-inverting amplifier if Vin = 10mV dc. Also draw i/p and o/p waveforms.Answer:-



Question: - Why open loop configuration of op- amp is never used for amplification? Give reasons.Answer:-

Since open-loop gain of the op-amp is very high, the clipping occurs in the open-loop configuration when the output attempts to exceed the saturation levels of the Op-Amp.

The open loop voltage gain of the op-amp is not constant. The gain varies with the changes in temperature and power supply. This makes op-amp unsuitable for the linear applications.

Open loop configuration of op-amp is never used for amplification because an amplifier requires linear relationship between input signal and output signal.

Therefore for very small input differential voltage (Vd) of the order of few microvolts, the op- amp output will reach saturation level (+Vsat or -Vsat) and linear relationship between input and output is not possible for input signal (Vd) beyond few microvolts.

Also there are problems of distortion, noise, low bandwidth in open loop mode. Hence op- amp is never used in open loop mode for amplification.

Closed loop configuration’s of Op-Amp:-1. Inverting amplifier.2. Non-inverting amplifier.3. Voltage amplifier.

Closed loop Inverting amplifier:-



o The circuit diagram of closed loop inverting amplifier is shown in the above figure.o The signal which is to be amplified is applied to the inverting terminal of the Op-Amp through

resistor R1.o The resistor RF, connected between the output terminal and the inverting terminal is called as

feedback resistor. It introduces negative feedback.o The non-inverting terminal is connected to ground.o The amplified output signal will be 180o out of phase with respect to the input signal.o As the output signal is in the inverted form of the input signal, therefore this amplifier is called

as inverting amplifier.o Input and output waveforms are shown below.

Derivation (expression) for closed loop voltage gain of the inverting op-amp:-



Closed loop non-inverting amplifier:-



o The circuit diagram of closed loop non-inverting amplifier is shown in the above figure.o The signal which is to be amplified is applied to the non-inverting terminal of the Op-Amp.o The resistor R1 is connected in between inverting terminal of op-amp and ground.o The resistor RF, connected between the output terminal and the inverting terminal is called as

feedback resistor. It introduces negative feedback.o The amplified output signal will be 0o or 360o phase shifted with respect to the input signal.o As the output signal is in phase with the input signal, therefore this amplifier is called as non-

inverting amplifier.o Input and output waveforms are shown below.

Derivation (expression) for closed loop voltage gain of the non-inverting op-amp:-



Question: - Design the circuit to get O/P voltage VO = 5Vi and draw design circuit.Prepared by: - Sudershan. Dolli V.V.P.Polytechnic, Solapur

Linear Integrated CircuitsAnswer:-

Design:-

Sr.No

Parameters Open-loop configuration Closed-loop configuration

1 Circuit diagram

2 Gain Voltage gain is very high Voltage gain is low as compared to open loop.

3 Bandwidth Bandwidth is low Bandwidth is high 4 Stability Less stable More stable5 Frequency response Frequency response has high gain and

less bandwidthFrequency response has low gain and

high bandwidth6 Feedback No feedback from output to input Feedback exists from output to input7 Input resistance Very high Low8 Disadvantage Cannot be used as amplifier, since output

gets distortedGain is low

9 Application Comparator It is used in amplifier, oscillator etc.

Voltage follower circuit (unity gain amplifier):-Prepared by: - Sudershan. Dolli V.V.P.Polytechnic, Solapur


o The lowest gain that can be obtained from a non-inverting amplifier with feedback is 1.o When non-inverting amplifier is configured for unity gain, it is called a voltage follower, because

the output is equal to and in phase with the input.o In other words, the output of voltage follower (unity gain amplifier) follows the input. o The voltage follower (unity gain amplifier) is preferred because it has much higher input

resistance and the output amplitude is exactly equal to input.o To obtain the voltage follower (unity gain amplifier) from the non-inverting amplifier, simply

open R1 and short RF.o The voltage follower is also called as a non-inverting buffer because, when placed between the

two networks, it removes the loading on the first network.

Virtual Ground Concept:-

OR

The voltage Vid = 0, implies that terminal 1 (inverting) has same potential at terminal 2 (non-inverting).

If the non-inverting terminal of OP-AMP is connected to ground then due to the virtual short existing between the two input terminals, the inverting terminal will also be at ground potential.

Hence it is said to be virtual ground Similarly, if the inverting terminal is connected to ground, then the non-inverting terminal will be at

virtual ground potential. Thus virtual ground point has a zero Voltage at terminal (inverting or non-inverting) and draws no

current. Due to zero potential at terminal (inverting or non-inverting) this concept is called Virtual ground concept.

The concept of virtual ground has been used extensively for amplifier analysis; especially we use this concept in the inverting amplifiers.

Summing amplifier or inverting Adder:-Prepared by: - Sudershan. Dolli V.V.P.Polytechnic, Solapur


o Figure shows the inverting configuration with three inputs Va, Vb, and Vc.o Depending on the relation between the feedback resistor (RF) and the input resistance Ra, Rb,

and Rc, the circuit can be used as summing amplifier.o The circuits function can be verified by examining the expression for output voltage VO.o So, applying Kirchhoff’s current law (KCL) to the node V2, we get:-

o Therefore, when the gain of the circuit is 1, i.e. RF/R=1, i.e. if Ra=Rb=Rc=RF, the output voltage is equal to the negative sum of the input voltages.

VO= - (Va+Vb+Vc)

Averaging amplifier:-



o Figure shows the inverting configuration with three inputs Va, Vb, and Vc.o The circuit can be used as averaging circuit, in which the output voltage is equal to the average

of all the input voltages.o This is accomplished by using all input resistors of equal values, Ra=Rb=Rc=R.o Also the gain of the circuit must be equal to 1 over the number of inputs, i.e. RF/R=1/n, where n

is number of inputs (3 input for above circuit)o Depending on the relation between the feedback resistor (RF) and the input resistance Ra, Rb, and

Rc, the circuit can be used as averaging amplifier.o The circuits function can be verified by examining the expression for output voltage VO.o So, applying Kirchhoff’s current law (KCL) to the node V2, we get:-


Linear Integrated CircuitsScaling amplifier or weighted amplifier:-

o Figure shows the inverting configuration with three inputs Va, Vb, and Vc.o If each input is amplified by different factor, i.e. weighted differently at the output, the circuit is

then called as scaling amplifier or weighted amplifier.o Depending on the relation between the feedback resistor (RF) and the input resistance Ra, Rb,

and Rc, the circuit can be used as scaling amplifier or weighted amplifier.o The circuits function can be verified by examining the expression for output voltage VO.o So, applying Kirchhoff’s current law (KCL) to the node V2, we get:-

o The condition can be accomplished if Ra, Rb, and Rc are different in value. Thus the output voltage of the scaling amplifier is derived above.


Linear Integrated CircuitsBasic integrator:-



Drawbacks of integrator:-

Compare active integrator and active differentiator:-



OR



Logarithmic amplifier:-



Window detector:-

Second order high pass filter:-



Band pass filter:-

Narrow band reject filter:-



IC 555:-



OR



IC 555 with touch plate:-

Or



Frequency divider using IC 555:-



PLL as frequency multiplier:-



Transfer characteristics of PLL:-

Astable multivibrator using IC 741:-



Schmtt trigger:-



Phase shift oscillator using IC 555:-

Voltage controlled oscillator using IC 555:-



Bistable multivibrator:-



Wein bridge oscillator:-


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