EC 6401 - ELECTRONIC CIRCUITS II

SUBJECT: EC 6401 -ELECTRONIC CIRCUITS II

EC 6401 -ELECTRONIC CIRCUITS II  - Download As PDF File

UNIT-I –FEEDBACK AMPLIFIERS

(TWOMARKS QUESTION AND ANSWERS)

1. What is meant by feedback?

A portion of the output signal is taken from the output of the amplifier and is

combined with the normal input signal. This is known as feedback.

(OR)

Feedback is a part of output is sampled and fedback to the input of the amplifier.

2. Give the different types of feedbacks used in amplifier circuits.

1. Positive feedback

2. Negative feedback.

3. Define the positive feedback.

When input signal and part of the output signal are in phase, the feedback is called

Positive feedback.

4. Define negative feedback.

When input signal and part of the output signal are in out of phase, the feedback is

called negative feedback.

5. What type of feedback is used in oscillator?

Positive.

6. Give classification of amplifiers.

The amplifiers can be classified into four broad categories: voltage, current,

Tranconductance and Tranresistance amplifiers.

7. What is node sampling?

When the output voltage is sampled by connecting the feedback network in shunt

across the output, the connection is referred to as voltage or node sampling.

8. What is loop sampling?

When the output current is sampled by connecting the feedback network in series

with the output, the connection is referred to as current or loop sampling.

9. Define feedback factor or feedback ratio.

The ratio of the feedback voltage to output voltage is known as feedback factor or

feedback ratio.

10. What is the purpose of mixer network in feedback amplifier?

The mixer network is used to combine feedback signal and input at input of an

amplifier.

11. What are the advantages of introducing negative feedback?

1. Input resistance is very high.

2. Output resistance is low.

3. The transfer gain Af of the amplifier with feedback can be stabilized against

Variations of the h-parameters or hybrid π parameters of the transistors or the

Parameters of the others active devices used in the amplifiers.

4. It improves the frequency response of the amplifiers.

5. There is a significant improvement in the linearity of operation of the feedback.

12. List the four basic feedback topologies.

1. Voltage amplifier with voltage series feedback.

2. Transconductance amplifier with current-series feedback.

3. Current amplifier with current-shunt feedback

4. Transresistance amplifier with voltage shunt feedback

13. Give the expression for gain of an amplifier with feedback.

Avf = AV/ 1+ AV β

Where, Avf – feedback voltage gain.

AV – Voltage gain.

β - Feedback factor

14. What is loop gain or return ratio.

A path of a signal from input terminals through basic amplifier, through the

feedback network and back to the input terminals forms a loop. The gain of this loop is

the product -A β . This gain is known as loop gain or return ratio.

15. What is sensitivity of the transfer gain?

The fractional change in amplification with feedback divided by the fractional

change without feedback is called the sensitivity of the transfer gain.

16. What is desensitivity?

The reciprocal of the sensitivity is called the desensitivity D. it is given as

D = 1+A β

17. What is the effect of lower cut-off frequencywith negative feedback?

Lower cutoff frequency with feedback is less than lower cutoff frequency without

feedback by factor (1+Amid β)

18. What is the effect of upper cut-off frequency with negative feedback?

Upper cutoff frequency with feedback is greater than upper cutoff frequency

without feedback by factor (1+Amid β)

19. What is the effect of negative feedback on bandwidth?

Bandwidth of amplifier with feedback is greater than bandwidth of amplifier

without feedback.

20. Why gain bandwidth product remains constant with the introduction of negative

feedback?

Since bandwidth with negative feedback increases by factor (1+A β) and gain

decreases by same factor, the gain-bandwidth product of an amplifier does not altered,

when negative feedback is introduced.

21. What is the effect of negative feedback on feedback distortion?

The frequency distortion is reduced with the negative feedback.

22. What is the effect of negative feedback on noise?

The noise is reduced with the negative feedback.

23. What is the effect of negative feedback on non linear distortion?

The linear distortion is reduced with the negative feedback.

24. What are the types of distortions in an amplifier?

1. Frequency

2. Noise and non linear

25. What type of feedback is employed in emitter follower amplifier?

Voltage series feedback.

26. A feedback amplifier has an open loop gain of 600 and feedback factor β = 0.01. Find

the closed loop gain with feedback.

Avf = AV/ 1+ AV β

= 600/ (1+ 600*0.01)

= 85.714.

27. The distortion in an amplifier is found to be 3%, when the feedback ratio of negative

feedback amplifier is 0.04.When the feedback is removed, the distortion becomes 15%.

Find the open and closed loop gain.

Solution:

Given: β = 0.04

Distortion with feedback = 3%,

Distortion without feedback = 15%

D = 15/3 = 5.

Where D = 1+A β =5

A = 100.

28. Which is the most commonly used feedback arrangement in cascaded amplifiers and

why?

Voltage series feedback is the most commonly used feedback arrangement in

cascaded amplifiers. Voltage series feedback increases input resistance and decreases

output resistance. Increase in input resistance reduces the loading effect of previous stage

and the decrease in output resistance reduces the loading effect of amplifier itself for

driving the next stage.

29. Voltage gain of an amplifier without feedback is 60dB. It decreases to 40dB with

feedback. Calculate the feedback factor.

Solution:

Given: Av = 60dB and Avf = 40 dB.

We know that,

Avf = AV / 1+ AVβ

β = (AV- Avf) / ( AVAvf)

= (60-40) / (60*40)

β = 0.00833.

30. State the nyquist criterion for stability of feedback amplifiers?

1. The amplifier is unstable if the curve encloses the point -1+j0. The system is

called as unstable system.

2. The amplifier is stable if the curve encloses the point -1+jo. That system is

called as stable system.

31. What is nyquist diagram?

The plot which shows the relationship between gain and phase-shift as a function

of frequency is called as nyquist diagram.

32. Write the steps which are used to identify the method of feedback topology?

1. Identify topology (type of feedback)

a) To find the type of sampling network.

b) To find the type of mixing network

2. Find the input circuit.

3. Find the output circuit.

4. Replace each active device by its h-parameter model at low frequency.

5. Find the open loop gain (gain without feedback), A of the amplifier.

6. Indicate Xf and Xo on the circuit and evaluate β = XfXO.

7. Calculate A, and β, find D, Ai,Rif,Rof,and Rof’.

UNIT-II –OSCILLATORS

1. What is an oscillator?

An oscillator is a circuit which basically acts as a generator, generating the

output signal which oscillates with constant amplitude and constant desired

frequency.

2. What is the difference between open loop and closed loop gain of the circuit?

S.NO Open loop gain Closed loop gain

1.

The gain of the amplifier is ratio

of output to input when no

feedback is used is called open

loop gain

The ratio of the output to input,

considering the overall effect of the

feedback is called closed loop gain.

3. State the Barkhausen criterion for an oscillator.

1. The total phase shift around a loop, as the signal proceeds from input

through amplifier, feedback network back to input again, completing a

loop, is precisely 00 or 3600.

2. The magnitude of the product of the open loop gain of the amplifier

(A) and the feedback factor β is unity. i.e., A β = 1.

4. Explain the concept of positive feedback.

The feedback is a property which allows to feedback the part of the output, to the

same circuit as its input. Such a feedback is said to be positive whenever the part tf the

output that is fed back to the amplifier as its input, is in phase with the original input

signal applied to the amplifier.

5. From where starting voltage for the oscillator is derived?

Every resistance has some free electrons. Under the influence of room

temperature, these free electrons move randomly in various directions. In such a

movement of the free electrons generate a voltage called noise voltage, across the

resistance. Such noise voltage provides the starting voltage for the oscillator.

6. Why in practice A β is kept greater than unity.

To amplify small noise voltage present, so that oscillations can start, A β is kept

initially greater than unity.

7. Give the over all classification of oscillators?

a. Waveform type (sinusoidal, square, triangular,etc.,)

b. Circuit components (LC, RC,etc.,)

c. Range of frequency –A.F (audio), R.F (radio)

d. Type of feedback (RC phase shift,Wein bridge are feedback used, UJT

relaxation oscillators uses no feedback)

8. What are the frequency sensitive arms?

The arms which decide the frequency of oscillations i.e., R1-C1 and R2-C2 are the

frequency sensitive arms.

9. What is the gain requirement in the wein bridge oscillator?

The gain requirement for wein bridge oscillator is minimum 3.

10. How to obtain Hartley oscillator from the basic form of LC oscillator

Using X1 and X2 as inductors and X3 as capacitor, Hartley oscillator from basic

form of LC oscillator is obtained.

11. How to obtained colpitt’s oscillator form basic form of LC oscillator?

Using X1 and X2 as capacitors and X3 as inductors, colpitt’s oscillator from basic

form of LC oscillator is obtained.

12. Write down the advantages of RC phase shift oscillator.

a) Simplicity of the circuit.

b) Useful for frequencies in the audio range.

c) A sine wave output can be obtained.

13. Write down disadvantages of RC phase shift oscillator.

a) Poor frequency stability.

b) It is difficult to get a variable frequency output, because to change the

frequency, we need to vary all the resistors and capacitors simultaneously which is

practically very difficult.

14. Write down the advantages, disadvantages and applications of Hartley oscillator.

Advantages:

a) It is easy to tune

b) It can operate over a wide frequency typically from few Hz and several MHz.

c) It is easy to change the frequency by means of a variable capacitor.

Disadvantages:

a) Poor frequency stability.

Applications:

a) it is used as local oscillator in radio and TV receivers.

b) In the function generator.

c) In RF sources

15. Write down the advantages, disadvantages and applications of colpitt’s oscillator.

Advantages:

a) Simple construction.

b) It is possible to obtain oscillations at very high frequencies.

Disadvantages:

a) It is difficult to adjust the feedback as it demands change in capacitor values.

b) Poor frequency stability.

Application:

a)     As a high frequency generator.

17. Write down the advantages, disadvantages and applications of crystal oscillator.

Advantages:

a) Very high frequency stability.

b) Very low frequency drift due to change in temperature and other parameters.

c) It is possible to obtain very high, precise and stable frequency of oscillations.

d) The Q is very high.

Disadvantages:

a) These are suitable for high frequency applications.

b) Crystals of low fundamental frequencies are not easily available.

Applications:

a) As a crystal clock in microprocessors.

b) In the frequency synthesizers.

c) In the radio and TV transmitters.

b)    d) In special types of receivers.

UNIT –III - TUNED AMPLIFIERS

1. What do you mean by tuned amplifiers?

The amplifiers which amplify only selected range of frequencies (narrow

band of frequencies) with the help of tuned circuits (parallel LC circuit) are called

tuned amplifiers.

2. What are the various types of tuned amplifiers?

(1) Small signal tuned amplifiers

a. Single tuned amplifiers

(i) Capacitive coupled

(ii) Inductively coupled (or) Transformer coupled

b. Double tuned amplifiers

c. Stagger tuned amplifiers

(2) Large signal tuned amplifiers

3. Give the expressions for the resonance frequency and impedance of the tuned

circuit.

f =

1

&

L

ZR =

2π LC CR

4. What is the response of tuned amplifiers?

The response of tuned amplifier is maximum at resonant frequency and it

falls sharply for frequencies below and above the resonant frequency.

5. When tuned circuit is like resistive, capacitive and inductive?

(1) At resonance, circuit is like resistive.

(2) For frequencies above resonance, circuit is like capacitive.

(3) For frequencies below resonance, circuit is like inductive.

6. What are the various components of coil losses?

(1) Copper loss

(2) Eddy current loss

(3) Hysteresis loss

7. Define Q factor of resonant circuit.

(1) It is the ratio of reactance to resistance.

(2) It also can be defined as the measure of efficiency with which inductor can

store the energy.

Q=2п *(Maximum Energy Stored per cycle / Energy dissipated per cycle)

8. What is dissipation factor?

(1) It is defined as 1/Q.

(2) It can be referred to as the total loss within a component.

9. Define unloaded and loaded Q of tuned circuit.

(1) The unloaded Q or QU is the ratio of stored energy to dissipated energy in

a reactor or resonator.

(2) The loaded Q or QL of a resonator is determined by how tightly the

resonator is coupled to its terminations.

10. Why quality factor is kept as high as possible in tuned circuits?

1. When Q is high, bandwidth is low and we get better selectivity. Hence Q is

kept as high as possible in tuned circuits.

2. When Q is high inductor losses are less.

11. List various types of cascaded Small signal tuned amplifiers.

1. Single tuned amplifiers.

2. Double tuned amplifiers.

3. Stagger tuned amplifiers.

12. How single tuned amplifiers are classified?

1. Capacitance coupled single tuned amplifier.

2. Transformer coupled or inductively coupled single tuned amplifier.

13. What are single tuned amplifiers?

Single tuned amplifiers use one parallel resonant circuit as the load

impedance in each stage and all the tuned circuits are tuned to the same

frequency.

14. What are double tuned amplifiers?

Double tuned amplifiers use two inductively coupled tuned circuits per

stage, both the tuned circuits being tuned to the same frequency.

15. What are stagger tuned amplifiers?

Stagger tuned amplifiers use a number of single tuned stages in cascade,

the successive tuned circuits being tuned to slightly different frequencies.

(OR)

It is a circuit in which two single tuned cascaded amplifiers having certain

bandwidth are taken and their resonant frequencies are adjusted that they are

separated by an amount equal to the bandwidth of each stage. Since resonant

frequencies are displaced it is called stagger tuned amplifier.

16. What is the effect of cascading single tuned amplifiers on bandwidth?

Bandwidth reduces due to cascading single tuned amplifiers.

17. List the advantages and disadvantages of tuned amplifiers.

Advantages:

1. They amplify defined frequencies.

2. Signal to Noise ratio at output is good.

3. They are well suited for radio transmitters and receivers.

4. The band of frequencies over which amplification is required can be varied.

Disadvantages:

1. Since they use inductors and capacitors as tuning elements, the circuit is bulky

and costly.

2. If the band of frequency is increased, design becomes complex.

3. They are not suitable to amplify audio frequencies.

18. What are the advantages of double tuned amplifier over single tuned amplifier?

1. It provides larger 3 dB bandwidth than the single tuned amplifier and hence

provides the larger gain-bandwidth product.

2. It provides gain versus frequency curve having steeper sides and flatter top.

19. What the advantages are of stagger tuned amplifier?

The advantage of stagger tuned amplifier is to have better flat, wideband

characteristics.

20. Mention the applications of class C tuned amplifier.

1. Class C amplifiers are used primarily in high-power, high-frequency

applications such as Radio-frequency transmitters.

2. In these applications, the high frequency pulses handled by the amplifier are

not themselves the signal, but constitute what is called the Carrier for the

signal.

3. Amplitude modulation is one such example.

4. The principal advantage of class-C amplifier is that it has a higher efficiency

than the other amplifiers.

21. What is Neutralization?

The technique used for the elimination of potential oscillations is called

neutralization. (OR) The effect of collector to base capacitance of the transistor

is neutralized by introducing a signal that cancels the signal coupled through

collector base capacitance. This process is called neutralization.

22. What is the use of Neutralization?

1. BJT and FET are potentially unstable over some frequency range due to the

feedback parameter present in them.

2. If the feedback can be cancelled by an additional feedback signal that is equal

in amplitude and opposite in sign, the transistor becomes unilateral from input

to output the oscillations completely stop.

3. This is achieved by Neutralization.

23. What are the different types of neutralization?

1. Hazeltine neutralization

2. Rice neutralization

3. Neutrodyne neutralization.

24. What is rice neutralization?

It uses center tapped coil in the base circuit. The signal voltages at the end

of tuned base coil are equal and out of phase.

UNIT-IV

WAVE SHAPING AND MULTIVIBRATOR CIRCUITS

1. What is High pass RC circuit? Why it is called high-pass filter?

1. A simple circuit consisting of a series capacitor and a shunt resistor is

called high pass RC circuit.

2. At very high frequencies the capacitor acts as a short circuit and all the

higher frequency components appear at the output with less attenuation than the

lower frequency components. Hence this circuit is called high-pass circuit.

2. Why high-pass RC circuit is called Differentiator?

High-pass RC circuit gives an output waveform similar to the first derivative

of the input waveform. Hence it is called Differentiator.

3. What is Low pass RC circuit? Why it is called low-pass filter?

1. A simple circuit consisting of a series resistor and a shunt capacitor is called

Low pass RC circuit.

2. At very high frequencies the capacitor acts as a virtual short circuit and

output falls to zero. Hence this circuit is called low-pass filter

4. Why low-pass RC circuit is called Integrator?

Low pass RC circuit gives an output waveform similar to the time integral of

the input waveform. Hence it is called Integrator.

5. What is High pass RL circuit? Why it is called high-pass filter?

1. A simple circuit consisting of a series resistor and a shunt inductor is called

high-pass RL circuit.

2. At very high frequencies, the inductor acts as an open circuit and all the

higher frequency components appear at the output. Hence this circuit is called

high-pass filter.

6. What is Low pass RL circuit? Why it is called low-pass filter?

1. A simple circuit consisting of a series inductor and a shunt resistor is called

low pass RL circuit.

2. At very high frequencies, the inductor acts as a virtual open circuit and the

output falls to zero. Hence this circuit is called low pass filter.

7. What is Delay time (td) in transistor?

The time needed for the collector current to rise to 10% of its maximum

(saturation) value i.e. iC(Sat) = VCC/RC is called the delay time.

8. What is Rise time (tr) in transistor?

The time required for the collector current to rise from 10% to 90% of the

maximum value is called rise time (tr).

9. What is Turn-ON time (tON) in transistor?

The sum of the delay time (td) and the rise time (tr) is called the turn-ON time

(tON).

tON = td + tr

10. What is storage time (ts) in transistor?

The time when collector current (iC) dropped to 90% of its maximum value

is called the storage time.

11. What is fall time (tf) in transistor?

The time required for the collector current to fall from 90% to 10% of its

maximum value is called fall time (tf).

12. What is Turn-off time (tOFF) in transistor?

The sum of the storage time (ts) and the fall time (tf) is called the turn-OFF

time (tOFF).

(tOFF) = (ts) + (tf)

13. What is clipper?

The circuit with which the waveform is shaped by removing (or clipping) a

portion of the input signal without distorting the remaining part of the alternating

waveform is called a clipper.

14. What are the four categories of clippers?

1. Positive clipper

2. Negative clipper

3. Biased clipper

4. Combination clipper

15. What is comparator?

1. The nonlinear circuit which was used to perform the operation of clipping

may also be used to perform the operation of comparison is called the comparator.

2. The comparator circuit compares an input signal with a reference voltage.

16. What is clamper?

A circuit which shifts (clamps) a signal to a different dc level, i.e. which

introduces a dc level to an ac signal is called clamper. It is also called dc restorer.

17. Which circuits are called multivibrators?

1. The electronic circuits which are used to generate nonsinusoidal waveforms

are called multivibrators.

2. They are two stage switching circuits in which the output of the first stage is

fed to the input of the second stage and vice-versa.

18. Which are the various types of multivibrators?

1. Astable multivibrator

2. Bistable multivibrator

3. Monostable multivibrator

19. What is astable multivibrator?

1. A multivibrator which generates square wave without any external

triggering pulse is called astable multivibrator.

2. It has both the states as quasi-stable states. None of the states is stable.

3. Due to this, the multivibrator automaticallymakes the successive transitions

from one quasi-stable state to other, without any external triggering pulse. So it

called Free-runningmultivibrator.

4. The rate of transition from one quasi-stable state to other is determined by

the discharging of a capacitive circuit.

20. List the applications of Astable multivibrator?

1. Used as square wave generator, voltage to frequency convertor and in pulse

synchronization, as clock for binary logic signals, and so on.

2. Since it produces square waves, it is a source of production of harmonic

frequencies of higher order.

3. It is used in the construction of digital voltmeter and SMPS.

4. It can be operated as an oscillator over a wide range of audio and radio

frequencies.

21. State the basic action of monostable multivibrator.

1. It has only one stable state. The other state is unstable referred as quasistable

state.

2. It is also known as one-short multivibrator or univibrator.

3. When an external trigger pulse is applied to the circuit, the circuit goes

into the quasi-stable state from its normal stable state.

4. After some time interval, the circuit automatically returns to its stable

state.

5. The circuit does not require any external pulse to change from quasistable

state.

6. The time interval for which the circuit remains in the quasi-stable state is

determined by the circuit components and can be designed as per the

requirement.

22. Mention the applications of one short multivibrator?

1. It is used to function as an adjustable pulse width generator.

2. It is used to generate uniform width pulses from a variable width pulse

train.

3. It is used to generate clean and sharp pulses from the distorted pulses.

4. It is used as a time delay unit since it produces a transition at a fixed time

after the trigger signal.

23. Which multivibrator would function as a time delay unit? Why?

Monostable multivibrator would function as a time delay unit since it

produces a transition at a fixed time after the trigger signal.

24. What is Bistable multivibrator?

1. The Bistable multivibrator has two stable states.

2. The multivibrator can exist indefinitely in either of the two stable states.

3. It requires an external trigger pulse to change from one stable state to

another.

4. The circuit remains in one stable state unless an external trigger pulse is

applied.

25. List the applications of bistable multivibrator?

1. It is used as memory elements in shift registers, counters, and so on.

2. It is used to generate square waves of symmetrical shape by sending

regular triggering pulse to the input. By adjusting the frequency of the

trigger pulse, the width of the square wave can be altered.

3. It can also be used as a frequency divider.

26. What are the two methods of triggering for bistable multivibrators?

1. Unsymmetrical triggering

2. Symmetrical triggering

27. How many stable states do bistable Multivibrator have?

Two stable states.

28. When will the circuit change from stable state in bistable Multivibrator?

When an external trigger pulse is applied, the circuit changes from one

stable state to another.

29. What are the different names of bistable Multivibrator?

Eccles Jordan circuit, trigger circuit, scale-of-2 toggle circuit, flip-flop and

binary.

30. What are the other names of monostable Multivibrator?

One-shot, Single-shot, a single-cycle, a single swing, a single step

Multivibrator, Univibrator.

31. Why is monostable Multivibrator called gating circuit?

The circuit is used to generate the rectangular waveform and hence can be

used to gate other Circuits hence called gating circuit.

32. What are the main characteristics of Astable Multivibrator?

The Astable Multivibrator automaticallymakes the successive transitions

from one quasi- stable State to other without any external triggering pulse.

33. What is the other name of Astable Multivibrator- why is it called so?

As it does not require any external pulse for transition, it is called free

runningMultivibrator.

34. What are the two types of transistor bistable Multivibrator?

i. Fixed bias transistor circuit

ii. Self bias transistor circuit.

35. Why does one of the transistor start conducting ahead of other?

The characteristic of both the transistors are never identical hence after

giving supplies one of the Transistors start conducting ahead of the other.

36. What are the two stable states of bistable Multivibrator?

i. Q1 OFF (cut off) and Q2 ON (Saturation)

ii. Q2 OFF (Cut off) and Q1 On (Saturation)

37. What finally decides the shape of the waveform for bistable multivibrator?

The spacing of the triggering pulses.

38. How are the values R1, R2 and VBB chosen in bistable Multivibrator?

It is chosen in such a way that in one state the base current is large enough

to drive the transistor into saturation while in other state the emitter

junctions is well below off.

39. What is the self biased Multivibrator?

The need for the negative power supply in fixed bias bistable

Multivibrator can be eliminated by raising a common emitter resistance

RE. The resistance provides the necessary bias to keep one transistor ON

and the other OFF in the stable state. Such type of biasing is called self

biasing and the circuit is called self biased bistable Multivibrator.

40. What are the other names of speed up capacitors?

i. Commutating Capacitors

ii. Transpose capacitors

41. Define transition time?

It is defined as the time interval during which conduction transfers from

one transistor to other.

42. What is the value of commutating capacitor?

It lies in the range of tens to some hundreds of Pico farads.

43. Define resolving time.

The smallest allowable interval between triggers is called resolving time.

44. Give the expression of fmax with respect to resolving time

Fmax = 1/resolving time.

45. Define gate width

The pulse width is the time for which the circuit remains in the quasi

stable state. It is also called gate width.

46. What is UTP of the Schmitt Trigger?

The level of Vi at which Q1 becomes ON and Q2 OFF is called Upper

Threshold Point.

47. What is the other name for UTP?

It is also called input turn on threshold level.

48. What is LTP of the Schmitt trigger?

The level of Vi at which Q1 becomes OFF and Q2 on is called Lower

Threshold Point.

49. Define transfer Characteristics

The graph of output voltage against input voltage is called transfer

characteristics of Schmitt trigger.

50. What is the important application of Schmitt trigger?

1. It is used as an amplitude comparator

2. It is used as a squaring circuit.

51. What is Schmitt trigger?

1. It is a wave shaping circuit, used for generation of a square wave from a

sine wave input.

2. It is a bistable circuit in which two transistor switches are connected

regeneratively.

52. What is meant by Hysteresis voltage in a Schmitt trigger?

1. The difference between UTP (Upper Threshold Point) and LTP (Lower

Threshold Point) is called Hysteresis voltage (VH).

2. It is also known as Dead Zone of the Schmitt trigger.

53. List the applications of Schmitt trigger.

1. It is used for wave shaping circuits.

2. It can be used for generation of rectangular waveforms with sharp edges

from a sine wave or any other waveform.

3. It can be used as a voltage comparator.

4. The Hysteresis in Schmitt trigger is valuable when conditioning noisy

signals for using digital circuits. The noise does not cause false triggering

and so the output will be free from noise.

54. How a Schmitt trigger is different from a multivibrator?

A Schmitt trigger has an input and an output; the output is a squared-up

version of the input. As long as the input is constant, the output of the

Schmitt trigger is also constant.

A multivibrator typically has no inputs (other than power), only an output:

an oscillating signal.

UNIT-V

BLOCKING OSCILLATORS AND TIME BASE GENERATORS

1. What is Blocking Oscillator?

A special type of wave generator which is used to produce a single narrow pulse

or train of pulses using regenerative feedback characteristics are called Blocking

oscillator.

2. What are Time Base generators?

The circuits which provide an output waveform, a part of which is characterized

by a linear variation of voltage or current with respect to time are called Time Base

generators.

3. What is UJT?

1. UJT is a three terminal semiconductor switching device.

2. As it has only one PN junction and three leads, it is commonly called as

Unijunction transistor.

4. What are the two important elements of Blocking Oscillator?

Transistor and pulse transformer

5. What are the applications of blocking Oscillator?

It is used in frequency dividers, counter circuits and for switching the other

circuits.

6. Give the expression for co-efficient of coupling

K=M/√LpLs

M-> Mututal Inductance

Lp -> Primary Inductance

Ls -> Secondary Inductance

7. Give the formula for transformation ratio

n= Ns/Np = transformation ratio

Ns= Secondary Turns;

Np= Primary turns

8. Define rise time.

It is defined by the time required by the pulse to rise from 10% of its amplitude to

90% of its amplitude.

9. Define overshoot.

It is the amount by which the output exceeds its amplitude during first attempt.

10. What is leading edge response?

At start there is an overshoot and then pulse settles down. The response till it

settles down after the overshoot is called leading edge response.

11. What is trailing edge response?

The response generally extends below the zero amplitude after the end of pulse

width is called back swing. The portion of response from back swing till it settles down is

called trailing edge response.

12. Define flat top response.

The portion of the response between the trailing edge and the leading edge is

called flat top response.

13. Define droop or a tilt.

The displacement of the pulse amplitude during its flat response is called droop or

a tilt.

14. What are the applications of pulse transformer?

Pulse transformer can be used to

1. Change the amplitude and impedance level of a pulse.

2. Invert the polarity of the pulse.

3. Produce a pulse in a circuit having negligible d.c. resistance.

4. Differentiate a pulse.

5. Act as a coupling element in a certain pulse generating circuits.

15. When does the core saturate?

When L->o as B-> Bm, the core saturates.

16. What is the other name of astable Blocking Oscillator?

Free running blocking Oscillator.

17. What are the two types of astable Blocking Oscillator?

1. Diode controlled Astable Blocking Oscillator.

2. Re controlled Astable Blocking Oscillator.

18. Define Sweep time in saw tooth generator.

The period during which voltage increases linearly is called sweep time.

19. What is the other name of saw tooth generator?

Ramp generator.

20. Define Displacement error in the saw tooth generator?

It is defined as the maximum differences between the actual sweep voltage and

linear sweep which passes through the beginning and end points of the actual sweep.

21. What is constant current charging?

A capacitor is charged with a constant current source.

22. What is the miller circuit?

Integrator is used to convert a step waveform into ramp waveform.

23. Mention the various methods of controlling the pulse.

1. Use of common base configuration.

2. Use of common collector configuration.

3. Use of core saturation method.

4. Use of shorted delay line.

24. What is mark space ratio?

The ratio of time for which Q is On to time for which Q is OFF is called markspace

ratio. If this is unity, then the output is almost symmetrical square wave.

25. Define Duty cycle.

The duty cycle is defined as the ratio of the ON time tp to the time period T.

Mathematically it is given by,

D= tp/T

26. How high duty cycle is obtained?

1. Using temperature compensated zener diode.

2. Using Ge diode in series with tertiary winding across the supply voltage.

27. What do you mean by voltage time base generators?

Circuits used to generate a linear variation of voltage with time are called Voltage

time-base generators.

28. What do you mean by linear time base generators/

Circuits provide an output waveform which exhibits a linear variation of voltage

with time are called linear time base generators.

29. Define restoration time or flyback time.

The time required for the return for the sweep voltage to the initial value is called

restoration time (or) return time (or) flyback time.

30. Define sweep time.

The period during which voltage increases linearly is called sweep time.

31. List important sweep parameters.

Sweep speed error, Displacement error and transmission error.

32. Name the different errors in generation of sweep waveforms.

Sweep speed error, Displacement error and transmission error.

33. Define Sweep speed error.

It is the ratio of difference in slope at beginning and end of sweep to the initial

value of slope.

34. Define Displacement error.

It is defined as the maximum difference between the actual sweep voltage and

linear sweep which passes through the beginning and end points of the actual sweep.

35. Define transmission error.

When a ramp voltage is transmitted through a high-pass RC network, its output

falls away from the input. The transmission error is defined as the difference between the

input and output divided by the input.