Post on 02-Jun-2018
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 1/30
Integrated Electronics
Lecture-11-13Pulse and Switching Circuits
1
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 2/30
Contents
• Pulse and switching circuits
• Types of Multivibrators
•
Multivibrators Designing• Types of Comparators
• Zero Level Detector
• Nonzero Level Detector
• Schmitt Trigger
2
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 3/30
Pulse and Switching Circuits
• An electronic oscillator is an electronic circuit
that produces a periodic, oscillating electronic
signal, often a sine wave or a square wave.
• There are two types of Oscillators
– Sinusoidal
– Non sinusoidal
• Multivibrator generates non sinusoidal waves.
3
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 4/30
Types of Multivibrators
1. Bistable Multivibrators
2. Astable Multivibrators
3. Monostable Multivibrators• Bistable: two stable states switched over from
one stable state to the other by the
application of an external trigger pulse thus, itrequires two external trigger pulses before it
returns back to its original state.
4
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 5/30
Types of Multivibrators
• Astable: in which the circuit is not stable ineither state—it continually switches from onestate to the other. It functions as a relaxationoscillator.
• Monostable: In a monostable multivibrator, oneof the state is absolutely permanent i.e, stableand the other one is temporary state. When anexternal trigger pulse is applied to the mono-
stable at appropriate point, the mono-stablechanges it state from stable state to temporarystate.
5
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 6/30
Designing of Multivibrators
• There are three methods of designing any
Multivibrators.
– By using Op-amp
– By using 555 timer IC
– Using discrete component like transistor
6
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 7/30
By using Op-amp
• Operational amplifiers are used as comparatorsto compare the amplitude of one voltage withanother.
• Op-amp is used in the open-loop configuration,with the input voltage on one input and areference voltage on the other.
• Comparator is a type of op-amp circuit thatcompares two input voltages and produces an
output in either of two states indicating thegreater than or less than relationship of theinputs.
7
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 8/30
Types of Comparator
– Zero level detector
– Non zero level detector
– Schmitt Trigger/Comparator with Hysterices
8
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 9/30
Zero-Level Detector
• Op-amp used as a comparatoris to determine when an inputvoltage exceeds a certain level.
• Whenever voltage on non-inverting terminal is greater
than the voltage on invertingterminal than the output ofop-amp would be positive andvice versa.
• Reference is set to zero andcompares with respect to set
zero reference.• Figure shows Zero Level
Detector.
9
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 10/30
Zero-Level Detector
• 741 IC open loop voltagegain is 1 lac.
• Output will not exceed Vcc.
• Output will be square.
• When the sine wave ispositive, the output is at itsmaximum positive level.
• When the sine wave crosses
0, the amplifier is driven toits opposite state and theoutput goes to its maximumnegative level.
10
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 11/30
Nonzero Level Detector
• Reference is set to non
zero voltage.
• Reference is always DC
• To detect positive andnegative voltages by
connecting a fixed
reference voltage
source to the inverting
input.
11
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 12/30
Nonzero Level Detector
• Find reference voltage
using voltage divider.
• By using voltage divider
we can changereference voltage by
changing the values of
resistor.
12
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 13/30
Nonzero Level Detector
• By using zener diode wecan set the referencevoltage because zenerdiode have specificvoltage levels (V
REF = V
Z).
• If Vin is less than VREF,the output remains at themaximum negative level.
• If input voltage exceeds
the reference voltage, theoutput goes to itsmaximum positivevoltage.
13
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 14/30
Nonzero Level Detector
14
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 15/30
Nonzero Level Detector Example
Example: The input signal in figure is applied to
the comparator circuit. Draw the output
showing its proper relationship to the input
signal. Assume the maximum output levels ofthe op-amp are ±12.
15
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 16/30
Nonzero Level Detector Example
Solution:
The reference voltage is set by R1 and R2 as
follows:
=
:(+V)=
.0ῼ
8.ῼ:.0ῼ +15
VREF = 1.63
16
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 17/30
Nonzero Level Detector Example
• Shown in figure, each
time input exceeds
+1.63V, the output
voltage switches to its+12V level, and each
time the input goes
below +1.63V, the
output switches back toits -12V level, neglecting
hysteresis.
17
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 18/30
Nonzero Level Detector Example
Example: Determine the reference voltage in
figure if R1 = 22K ῼ and R2 = 3.3K ῼ.
18
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 19/30
Effects of input noise on comparator
operation
• In many practical
situations, noise
appears on the input
line.• This noise voltage
superimposed on the
input voltage shown in
figure.
19
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 20/30
Schmitt Trigger
• Figure shows the inputsine wave plus noise andthe resulting output.
• When sine wave
approaches 0, thefluctuations due to noisecause the total input tovary above and below 0
several times, thusproducing an erraticoutput voltage.
20
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 21/30
Schmitt Trigger
• In order to make thecomparator less sensitiveto noise, a techniqueincorporating positivefeedback, calledhysteresis, can be used.
• Uses op-amp in +vefeedback configuration
• Using Schmitt trigger we
have two referencevoltages – VUTP = Upper trigger point
– VLTP = Lower trigger point
21
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 22/30
Schmitt Trigger
• Two type of Schmitt trigger
– Inverting Schmitt trigger
– Non Inverting Schmitt trigger.
• Schmitt trigger converts analog signal to
digital signal.
22
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 23/30
Schmitt Trigger Operation
• The operation of thecomparator withhysteresis shown infigure.
• Assume that the outputvoltage is at its positivemaximum, +Vout(max).
• The voltage feedback tothe non-inverting inputis VUTP and is expressedas:
23
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 24/30
Schmitt Trigger Operation
• When Vin exceeds, -
Vout(max).
• The voltage feedback to
the non-inverting inputis VLTP and is expressed
as:
24
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 25/30
Schmitt Trigger Operation
25
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 26/30
Schmitt Trigger
• Comparator with hysteresis is also known as
Bistable Comparator.
• Operated in two stable states either +ve or –
ve (Saturation).
• Hysteresis because it has dual threshold
action.
• Hysteresis voltage is calculated as:
VH = VUTP - VLTP
26
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 27/30
Example
• Determine the upper and lower trigger points
for the comparator circuit in figure. Assume
that +Vout(max) = +5V and –Vout(max) = -5V
27
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 28/30
Example
28
Example: Calculate the upper and lower
trigger points for the circuit shown in figurebelow. Assume the maximum output voltage
levels of op-amp are ±7.
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 29/30
Example
• Determine the switchingthreshold and hysteresis forthe following circuit.Assume that Vcc = 10 and
VEE = -10VUTP =
:=
0 ∗9.
9.: = 9.01
VLTP =
:=
0 ∗9.
9.: = -
9.01
Hystersis VH = VUTP-VLTP = 9.01-(-9.01)
VH = 18.02
29
8/10/2019 Lecture-11-13 Pulse and Switching Circuits
http://slidepdf.com/reader/full/lecture-11-13-pulse-and-switching-circuits 30/30
END OF LECTURE-11-15
30