lecture-11-13 pulse and switching circuits

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



Contents

• Pulse and switching circuits

• Types of Multivibrators

•

Multivibrators Designing• Types of Comparators

• Zero Level Detector

• Nonzero Level Detector

• Schmitt Trigger

2



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



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



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



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



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



Types of Comparator

– Zero level detector

– Non zero level detector

– Schmitt Trigger/Comparator with Hysterices

8



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



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



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




• Find reference voltage

using voltage divider.

• By using voltage divider

we can changereference voltage by

changing the values of

resistor.

12




• 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




14



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




Solution:

The reference voltage is set by R1 and R2 as

follows:

=

:(+V)=

.0ῼ

8.ῼ:.0ῼ +15

VREF = 1.63

16




• 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




Example: Determine the reference voltage in

figure if R1 = 22K ῼ and R2 = 3.3K ῼ.

18



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



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



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



Schmitt Trigger

• Two type of Schmitt trigger

– Inverting Schmitt trigger

– Non Inverting Schmitt trigger.

• Schmitt trigger converts analog signal to

digital signal.

22



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




• When Vin exceeds, -

Vout(max).

• The voltage feedback to

the non-inverting inputis VLTP and is expressed

as:

24




25



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



Example

• Determine the upper and lower trigger points

for the comparator circuit in figure. Assume

that +Vout(max) = +5V and –Vout(max) = -5V

27



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.



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



END OF LECTURE-11-15

30

lecture-11-13 pulse and switching circuits

Documents