18ECC205J ANALOG INTEGRATED CIRCUITS

UNIT – I (FEEDBACK AMPLIFIERS)

2 MARK QUESTIONS

1. Define 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.

2. Define positive feedback?

If the feedback signal is in phase with input signal, then the net effect of the feedback will
increase the input signal given to the amplifier. This type of feedback is said to be positive or
regenerative feedback.

3. Define negative feedback?

If the feedback signal is out of phase with the input signal then the input voltage applied to
the basic amplifier is decreased and correspondingly the output is decreased. This type of
feedback is known as negative or degenerative feedback.

4. Define sensitivity?
Sensitivity is defined as the ratio of percentage change in voltage gain with feedback to the
percentage change in voltage gain without feedback.
dAf/A=( dA/A)(1/1+βA)

5. What are the types of feedback?

i. Voltage-series feedback
ii. Voltage-shunt feedback
iii. Current-series feedback
iv. Current-shunt feedback

6. What are the basic amplifiers?

The basic amplifiers are
i. Voltage amplifier
ii. Current amplifier
iii. Transconductance amplifier
iv. Transresistance amplifier.

7. What are the components of feedback amplifier?

The components are
i. Sampling network,
ii. Feedback network, and
iii. mixer network.

8. What are two types of sampling?

i.Voltage sampling or node sampling
ii.Current sampling or loop sampling
9. State the two types of mixing?
Series mixing
Shunt mixing

10. What is transfer gain?

It is the ratio of the output signal to the input signal. It is denoted by A
A=Xo/Xi

11. List out the characteristics of feedback amplifier?

Desensitivity
Nonlinear distortion
Noise distortion
Frequency distortion

12. What is the effect of input resistance due to series mixing?

The input resistance increases due to series mixing irrespective of the type of sampling. The
feedback signal opposes the source signal and the input current decreases and due to this
input resistance increases.
Rif>Ri
Where Rif = input resistance with feedback
Ri = input resistance without feedback

13. What is the effect of input resistance due to shunt mixing?

The input resistance decreases due to shunt mixing irrespective of the type of sampling. The
feedback signal opposes the source signal and the input current decreases as a consequence
Voltage reduces leading to a reduction in input resistance.
Rif<Ri;
Where Rif = input resistance with feedback
Ri = input resistance without feedback

14. What happens to output resistance due to current sampling?

The output resistance increases due to current sampling.
Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback

15. What happens to output resistance due to voltage sampling?

The output resistance decreases due to current sampling.
Rof<Ro
Rof = input resistance with feedback
Ro= input resistance without feedback

16. What happens to output resistance due to current sampling?

The output resistance increases due to current sampling.
Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
17. Write the expression for input and output resistance of voltage series feedback
amplifier.
Input resistance with feedback, Rif = Ri(1+βA)
Output resistance with feedback, Rof = Ro(1+βA)

18. Give the properties of negative feedback.

i. Negative feedback reduces the gain
ii. Distortion is very much reduced

19. Give the effect of negative feedback on amplifier characteristics.

Types of feedback
Characteristics
Current-series Voltage-series Voltage-shunt Current-shunt

Voltage gain Decreases Decreases Decreases Decreases

Bandwidth Increases Increases Increases Increases

Input resistance Increases Increases Decreases Decreases

Output Increases Decreases Decreases Increases

Resistance

20. What are the effects of negative feedback? (Or) What are the advantages of negative
feedback?
1. It improves the stability of the circuit.
2. It improves the frequency response of the amplifier.
3. It improves the percentage of harmonic distortion.
4. It improves the signal to noise ratio (SNR).
5. It reduces the gain of the circuit.

21.Define the feedback factor β?

It is the ratio between the feedback voltages to the output voltage of the amplifier.
β = Vf/ Vo
Where, β is a feedback factor (or) feedback ratio, Vf is the feedback voltage, Vo is the output
voltage.

22 . Define Desensitivity D?
Desensitivity is defined as the reciprocal of sensitivity. It indicates the factor by which the
voltage gain has been reduced due to feedback network.
Desensitivity factor (D) = 1+A β.
Where, A = Amplifier gain.
β = Feedback factor.

23. Define loop gain. (Or) What is meant by return ratio?

The signal Vi is multiplied by ‘A’ in passing through the amplifier is multiplier by ‘β’. In
transmission through the feedback network and is multiplied by ‘-1’ in the mixer. The product
of ‘- A β’ is called the loop gain (or) return ratio
24. What is the nature of input and output resistance in negative feedback?
(1) Voltage series feedback:
Input impedance: Zif = Zi / (1+A β)
Output impedance: Zof = Zo / (1+A β)
(2) Voltage shunt feedback:
Input impedance: Rif = Ri * (1+A β)
Output impedance: Zof = Zo * (1+ A β)
(3) Current series feedback:
Input impedance: Rif = Zi / (1+A β)
Output impedance: Zof = Zo / (1+A β)
(4) Current shunt feedback:
Input impedance: Rif = Ri / (1+A β)
Output impedance: Rof = Ro / (1+A β)

OSCILLATOR
1. How does an oscillator differ from an amplifier?

Oscillators Amplifiers
1. They are self-generating circuits. They generate 1. They are not self-generating circuits.
waveforms like sine, square and triangular They need a signal at the input and they
waveforms of their own. Without having input just increase the level of the input
signal. waveform.
2. It have infinite gain 2. It have finite gain
3. Oscillator uses positive feedback 3. Amplifier uses negative feedback.

2. What is an Oscillator?
An Oscillator is a Circuit, which generates an alternating voltage of any desired frequency. It
can generate an a.c output signal without requiring any externally applied input signal.

3. What is Barkhausan criterion?

The conditions for oscillator to produce oscillation are given by Barkhausan criterion. They
are:
(i). the total phase shift produced by the circuit should be 360o or 0o
(ii).The Magnitude of loop gain must be greater than or equal to 1 i.e. ‫׀‬A .β ‫≥׀‬1.

4. What are the types of sinusoidal oscillator? Mention the different types of sinusoidal
oscillator?
1. RC phase shift Oscillator.
2. Wein Bridge Oscillator.
3. Hartley Oscillator
4.Colpitts Oscillator
5. Crystal Oscillator

5. Name two low frequency Oscillators.

1. RC phase shift. 2. Wein bridge Oscillator.
6. Name two high frequency Oscillators.
i. Hartley Oscillator ii. Colpitts Oscillator iii.Crystal Oscillator

7. What did you understand by the term stability of an Oscillator? (Or) ii). Define
stability of an Oscillator. (Or) iii). Why is amplitude stabilization required?
The frequency stability of an Oscillation is a measure of its ability to maintain the required
frequency as precisely constant as possible over a long period of time interval.

8. What are the essential parts of an Oscillator?

i. Tank circuit (or) Oscillatory circuit.
ii. . Amplifier (Transistor amplifier)
iii. . Feedback Circuit.

9. What are the advantages of Rc phase shift Oscillator?

i. It is best suited for generating fixed frequency signals in the audio frequency range.
ii.Simple Circuit. Iii Pure sine wave output is possible.

10. What is piezo electric effect?

The piezo electric Crystals exhibit a property that if a mechanical stress is applied across one
face the electric potential is developed across opposite face. The inverse is also live. This
phenomenon is called piezo electric effect.

11. Draw the equivalent circuit of a Crystal.

Where
R = internal frictional losses.
L = Mass of the crystal.
Cs = Stiffness of the crystal.
Cp = Shunt capacitance.

12. List the disadvantages of crystal Oscillator.

1. It is suitable for only low power circuits
2. Large amplitude of vibrations may crack the crystal.
3. It large in frequency is only possible replacing the crystal with another one by different
frequency.

13. What is meant by resonant Circuit Oscillators?

LC Oscillators are known as resonant circuit oscillator because the frequency of operation of
LC Oscillator is nothing but a resonant frequency of tank circuit or LC tank circuit produces
sustained Oscillation at the resonant circuit oscillator.
14. Classify the different types of Oscillators.
i. According to waveform generation
a. Sinusoidal Oscillator.
b. Relaxation Oscillator.
ii. According to the fundamental mechanism involved
a. Negative resistance Oscillator.
b. Feedback Oscillator.
iii. According to frequency generated
a. Audio frequency Oscillator (Up to 20KHZ)
b. Radio frequency Oscillator (20KHZ)
c. Very high frequency oscillator (30 MHZ to 300 MHZ).
d. Ultra high frequency Oscillator (300 MHX to 3 GHZ).
e. Microwave frequency Oscillator (> 3 GHZ).
iv. According to type coupling.
a. LC Oscillator.
b. RC Oscillator.

15. Why RC phase shift is needed in a RC phase shift Oscillator?

The amplifier used causes a phase shift of 180o than the feedback network should create
phase shift of 180o, to satisfy the Barkhausen Criterion. Hence in a phase shift oscillators,
three sections of RC circuit are connected in cascade, each introducing a shift of 60o, thus
introducing a total phase shift of 180o, due to feedback network.

16. What are the advantages of crystal Oscillators over other Oscillator?
To maintain the output frequency of an oscillator at a constant value, a crystal may be used to
control the frequency of oscillation.

17. What is negative resistance? Name a few devices which offer this resistance.
It is defined as the resistance of a device which offers when operated in the negative
resistance region.
Ex: - Tunnel diodes, UJT... Etc.,

18. Define gain and phase Margin.

Gain Margin: It is defined as the value of /Aβ/ in decibels at the frequency at which the
phase angle of Aβ is 180o, negative gain margin signifies decibel rise in open loop gain a
theoretical possibility without oscillation. A positive gain margin signifies that amplifier is
potentially unstable.
Phase Margin: It is defined as 1800 minus the Magnitude of angle of Aβ at the frequency at
which /Aβ/ is unity.

19. What is a beat frequency oscillator?

Beat frequency Oscillator (BFO) is an Oscillator in which a deserved signals frequency such
as the beat frequency produced by combining the different signal frequencies such as on
different radio frequencies.

20. what is frequency stability of oscillator?

The ability to measure the the stability of frequency over a long period of time & as long as
same desired frequency is measured.
 16 MARK QUESTIONS

1. Derive the expressions for gain with positive and negative feedback.
2. What is the effect of negative feedback on stability, distortion, noise, input and output
impedance of a feedback amplifier?
3. An amplifier, without feedback, has a voltage gain of 500, lower cut-off frequency f1 = 100
Hz, upper cut-off frequency f2 = 250 KHz and a distortion of 10%. Determine the amplifier
voltage gain, lower cut-off frequency and upper cut-off frequency and distortion, when a
negative feedback is applied with feedback ratio of 0.01.
4. An amplifier, with feedback has voltage gain of 100. When the gain without feedback
changes by 20 % and the gain with feedback should not vary more than 2 %. If so, determine
the values of open loop gain A and feedback ratio β.
5. What is the effect of a voltage series feedback on input and output resistance of a BJT
amplifier? Explain the same, with necessary circuit, equivalent circuit and equations.
6. Draw the circuit diagram of voltage shunt feedback amplifier and derive the expressions for
Rif and Rof.
7. With block diagram of current series feedback and derive the expressions for Rif and Rof.
8. Explain Nyquist criterion to analyse the stability of feedback amplifiers.
9. Derive the general condition for oscillation for a LC oscillator and derive the frequency of
oscillation for a colpitts oscillator.
10. Explain the working of a Hartley oscillator with a neat circuit diagram and derive the
frequency of oscillation.
11. Derive the expressions for frequency of oscillation and condition for sustained oscillation
of Hartley oscillator with neat circuit diagram.
12.A Hartley oscillator has L1 = 5 mH, L2= 25 mH and frequency of oscillation ranging from
700 KHz to 1 MHz. Determine the value of Cover this frequency range.
13. With neat circuit diagrams explain the working principle of the following:
• Tuned collector oscillator
• Franklin oscillator
• Armstrong oscillator
14. What is a Wien Bridge? How is it used as an oscillator? Derive the necessary equations.
15. Draw the circuit diagram and explain the working principle of RC phase shift oscillator.
Also derive the expression for frequency of oscillation and condition for
Sustained oscillation.
16. Explain the working of Clap oscillator with neat circuit diagrams. Give two applications.
 UNIT – II (TUNED AMPLIFIERS AND BLOCKING OSCILLATORS)

2 MARK QUESTIONS

1. What is a tuned amplifier?

The amplifier with a circuit that is capable of amplifying a signal over a narrow band of
frequencies are called tuned amplifiers.

2. What is the expression for resonant frequency?

fr=1/2π c

3. What happens to the circuit above and below resonance?

Above resonance the circuit acts as capacitive and below resonance the circuit acts as inductive.

4. What are the different coil losses? Hysteresis loss

Copper loss
Current loss

5. What is Q factor?
It is the ratio of reactance to resistance.

6. What is dissipation factor?

It is referred as the total loss within a component i.e 1/Q

7. What is the classification of tuned amplifiers?

Single tuned
Double tuned
Stagger tuned

8. is a single tuned amplifier?

An n amplifier circuit that uses a single parallel tuned circuit as a load is called single tuned
amplifier.

9. What are the advantages of tuned amplifiers

They amplify defined frequencies.
Signal to noise ratio at output is good
They are suited for radio transmitters and receivers

10. What are the disadvantages of tuned amplifiers?

The design is complex,
They are not suited to amplify audio frequencies.

11. What is neutralization?

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.

12. What are double tuned amplifiers?

The amplifiers having two parallel resonant circuit in its load are called double tuned amplifiers.
13. What is a stagger tuned amplifier?
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.

14. What are the advantages of stagger tuned amplifier?

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

15. What are the advantages of double tuned over single tuned?
1. Possess flatter response having steeper sides
2. Provides larger 3 db bandwidth
Provides large gain-bandwidth product.

16. What are the different types of neutralization?

1. Hazeltine neutralization
2. Rice neutralization
3. Neutrodyne neutralization.

17. 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.

18. What is unloaded Q?

It is the ratio of stored energy to the dissipated energy in a reactor or resonator.

19. What are the applications of mixer circuits?

Used in radio receivers. Used to translate signal frequency to some lower frequency

20. What is up converter?

When the mixer circuit is used to translate signal to high frequency, then it is called up converter.

21.What is an amplifier?
An amplifier is a device which produces a large electrical output of similar characteristics to that
of the input parameters.

22. How are amplifiers classified according to the input?

1. Small – signal amplifier 2. Large – signal amplifier

23. How are amplifiers classified according to the transistor configuration?

1. Common emitter amplifier 2. Common base amplifier 3. Common collector amplifier

24. What is the different analysis available to analyze a transistor?

1. AC analysis 2. DC analysis

25. How can a DC equivalent circuit of an amplifier be obtained?

By open circuiting the capacitor.

26. How can a AC equivalent circuit of a amplifier be obtained?

By replacing dc supply by a ground and short- circuiting capacitors.
 BLOCKING OSCILLATOR
1. Define Blocking Oscillator?
A special type of wave generator which is used to produce a single narrow pulse or train of pulses.

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

Transistor and pulse transformer

3. What are the applications of blocking Oscillator?

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

4. Give the expression for co-efficient of coupling

K=M/SQRT(LpLs)
M-> Mututal Inductance
Lp -> Primary Inductance
Ls -> Secondary Inductance

5. Give the formula for transformation ratio

n= Ns/Np = transformation ratio
Ns= Secondary Turns;
Np= Primary turns

6. 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.

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

8. Define flat top response.

The position of the response between the trailing edge and the leading edge.

9.Define droop or a tilt

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

10. What are the applications of pulse transformer.

i. to invert the polarity of the pulse
ii. to differentiate pulse

11. When do the core saturates?

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

12.What is the other name of astable Blocking Oscillator

Free running blocking Oscillator
13..What are the two types of astable Blocking Oscillator?

1. Diode controlled Astable Blocking Oscillator.

2. Re controlled Astable Blocking Oscillator.

14. Define Sweeptime in sawtooth generator

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

15. Define Displacement error in the sawtooth generator?

It is defined as the maximum differenece between the actual sweep voltage and linear sweep which
passes through the beginning and end points of the actual sweep.

16. What is constant current charging?

A capacitor is charged with a constant current source.

17. What is the miller circuit

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

18. 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.

19. Define overshoot.

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

20. Define flat top response.

The position of the response between the trailing edge and the leading edge.

21. Define droop or a tilt

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

22. What are the applications of pulse transformer.

i. to invert the polarity of the pulse
ii. to differentiate pulse

16 MARK QUESTIONS

1. Derive the Q factor for inductor.

2. Draw the circuit diagram and equivalent circuit of a capacitor coupled single tuned amplifier
and derive the expression for 3 – dB bandwidth. Sketch also the frequency response of the
amplifier.
3. With neat circuit diagram explain double tuned amplifier and derive the expression for 3 –
dB bandwidth. Sketch also the frequency response of the amplifier.
4. Draw the circuit diagram of a two-stage synchronously tuned amplifier and also its
equivalent circuit. Derive the expression for bandwidth.
5. A single tuned transistor amplifier is used to amplify modulated RF carrier of 600 KHz and
a bandwidth of 15 KHz. The circuit has total output resistance Rt = 20 K_ and output
capacitance Co = 50 pF. Calculate the values of inductance and
capacitance of tuned circuit.
6. Discuss the effect of bandwidth on cascading single tuned amplifiers.
7. Explain class C tuned amplifier and derive its efficiency. Also discuss about its frequency
response.
8. Explain the following with neat circuit diagram:
Hazeltine neutralization
9. Explain the Small signal tuned amplifier with necessary derivations.
10. Describe the principles involved in stagger tuned amplifier.
11. With circuit diagram and waveforms, explain the operation of a RC controlled astable
transistor blocking oscillator.
12. How does an Astable circuit acts as a free running blocking oscillator? Draw the circuit
and explain.
13. Compare RC controlled and Diode controlled Astable blocking oscillator.
14. Describe the operation of a triggered blocking oscillator with emitter timing. Sketch
the circuit and waveforms and also derive the expression for tp.
15. With suitable circuit and waveforms, explain the working of UJT saw tooth generator.
Derive the expression for the oscillating frequency.
16. For a certain UJT sweep circuit, the resistance is 20 K_ while the capacitance is 0.2 μF.
The valley potential is 1.5 V when VBB = 15 V. Assuming diode cut in voltage of 0.7 V
and intrinsic stand-off ratio as 0.5, calculate the frequency of oscillations.
17. Write about Miller integrator and current time-base circuit waveforms.