PAPER NAME: ECE 2101

PAPER CODE: Analog Circuits

2. (a) What is a load line? Explain the concept of Q-point.

(b) For CE configuration prove that IC = βIB + (1+β)ICO, where the symbols have their usual meaning.
(c) In a collector to base bias circuit indicated in Fig. 1, a transistor with β = 50 is used. Supply voltage
VCC = 10V, VBE = 0.7V, collector resistor RC = 2kΩ. The bias is obtained by connecting 100kΩ resistor
RB from collector to base. Find the Q-point and stability factor.

Fig.1

3. (a) Draw the hybrid parameter model of a Bipolar Junction Transistor.

(b) Assuming a BJT in CE mode, find the voltage gain, current gain, input impedance, output
impedance using h-parameter model.

4. (a) The input signal Vi is a sinusoid having an amplitude of 10V, VB1=8V and VB2=6V. Draw the output
voltage waveform Vo. Diodes D1 and D2 are ideal.

Fig.2
(b) Explain the operation of a positive clamper circuit with the help of a circuit diagram and input
output waveforms.

5. (a) For RC coupled amplifiers explain the effect of bypass capacitor on voltage gain.

(b) In a fixed bias circuit indicated in Fig. 3. Rb = 1MΩ, Rc = 5kΩ, VCC = 6V, β = 100, and neglect VBE.
Determine Q point, draw dc load line and determine the stability factor.

Fig. 3
 (c) Describe the voltage divider biasing circuit for npn BJT and explain how it provides compensation
against any change in the collector current.

6. (a) Using proper circuit diagram, explain operations of series and parallel clipper circuits. In each
case, compare the output waveform with the input waveform.
(b) In the circuit indicated in Fig. 4, a Bipolar Junction Transistor (BJT) is biased using a voltage-
divider configuration. The circuit parameters are: 𝑉𝐶𝐶 = 12 V, 𝑅1 = 50kΩ, 𝑅2 = 10𝑘Ω, 𝑅𝐶 =
2.2kΩ, 𝑅𝐸 = 1𝑘Ω, 𝛽 = 100 (current gain of the transistor), 𝑉𝐵𝐸 ≈ 0.7 V.
(i) Calculate the base current 𝐼𝐵 , the collector current 𝐼𝐶 , and the emitter current 𝐼𝐸 .
(ii) Determine the Q-point (collector-emitter voltage 𝑉𝐶𝐸 and collector current 𝐼𝐶 ) of the
transistor.

Fig. 4

7. (a) Draw a biasing configuration for collector feedback circuit and derive necessary equations for the
Q-point and stability factor.
(b) Consider a collector feedback biasing circuit with the following parameters: 𝑉𝐶𝐶 = 12 V, 𝑅𝐶 =
4.7𝑘Ω, 𝑅𝐵 = 220𝑘Ω, 𝛽 = 100, 𝑉𝐵𝐸 ≈ 0.7 V. Calculate the stability factor 𝑆 for this circuit.

8. (a) Derive expressions for small signal voltage gain and input impedance for the voltage divider
biasing configuration. Assume the BJT is an ideal one. Remark on the necessity of the bypass
capacitor.

(b) An ideal BJT CE amplifier has the following h-parameters and circuit details:
ℎ𝑓𝑒 = 150, ℎ𝑖𝑒 = 1.2𝑘Ω, 𝑅𝐶 = 2.7 kΩ, Load resistance 𝑅𝐿 = 3kΩ, Source resistance
𝑅𝑆 = 500Ω, 𝑅𝐸 = 1.0𝑘Ω
(i) Calculate the input impedance 𝑍in of the amplifier.
(ii) Calculate the voltage gain 𝐴𝑉 of the amplifier.

9. (a) Why is the stability of Q point essential? Derive the stability factor (with respect to I CO) for a
collector to base bias circuit.
(b) In the fixed bias circuit as shown in Fig 5. VCC=15V, RC=2 kΩ, RB=300 kΩ, β=100, VBE=0.7V. Neglect
ICO. Determine
(i) Base current IB
(ii) The quiescent point

Fig. 5.

10. (a) Using high-frequency model of BJT draw the equivalent circuit of a Common Emitter BJT amplifier
including coupling, parasitic and wiring capacitors.
 (b) List the advantages of negative feedback. A Hartley oscillator is designed with inductors L1=10μH
and L2=15μH, and a capacitor C=100pF. Calculate the oscillation frequency. (Neglect the effect of
mutual inductance).

11. (a) Derive the Barkhausen criterion of oscillation that must be satisfied by a feedback amplifier to
produce steady state oscillations.
(b) A Wien-Bridge oscillator has ( R1 = R 2 = 100 kΩ ) and ( C1 = C2 = 10 nF ). Calculate the
frequency of oscillation.
(c) Explain how the angle criteria of the Barkhausen criterion is satisfied in the Phase shift oscillator
with the help of its circuit diagram.

12. (a) Draw the circuit diagram of Phase Shift oscillator. Find an expression for the frequency of
oscillation and the condition for sustained oscillation.
(b) A phase shift oscillator uses 5pF capacitors. Find the value of R to produce a waveform having
frequency of 800kHz.

13. (a) Derive the general equation for a LC oscillator.

(b) A Colpitts oscillator is designed with C1=0.0001 μF and C2=0.01 μF. The inductance is variable.
Determine the range of inductance value if the frequency of oscillation is to vary between 950kHz
to 2050 kHz.
14. (a) Write short notes on the following: (i) Crystal oscillator (ii) Role of coupling capacitors, wiring,
and parasitic capacitances in limiting frequency response of BJT amplifier circuits.

(b) Design a Phase-Shift Oscillator to generate a frequency of 10 kHz. Assume the necessary
component values and show the calculations.
15. (a) With the help of a circuit diagram, explain the working of a Hartley Oscillator. Derive the
expression for the frequency of oscillation in terms of inductance and capacitance in the Hartley
Oscillator circuit.
(b) A Hartley Oscillator uses two inductors of values 2 mH and 3 mH in the tank circuit along with a
100 pF capacitor. Calculate the frequency of oscillation. (Neglect the effect of mutual inductance)

16. (a) With the help of a circuit diagram, explain the working of a Colpitts Oscillator. Derive the
expression for the frequency of oscillation in terms of inductance and capacitance in the Colpitts
Oscillator circuit.
(b) Classify oscillators based on (i) Shape of waveform (ii) Frequency of oscillation
17. (a) Sketch the circuit diagram of a Wien Bridge oscillator. Calculate the frequency of the
oscillation and the condition for sustained oscillation.
(b) A Wien Bridge oscillator has a frequency of oscillation1 kHz and a capacitance of 100pF. Find the
value of resistance required.

18. (a) What are the advantages of differential amplifier? Draw the circuit of dual input balanced output
differential amplifier.
(b) Design the equation with suitable block diagram in which output voltage, Vout = (V 12/3+V23/4),
where, V1 and V2 are the input voltages.

19. (a) Draw the block diagram of an OP-AMP showing the different building blocks. List the
characteristics of an ideal OP-AMP.
(b) Explain with neat circuit diagram how an op amp is used to obtain antilogarithm of a signal,
preventing variation due to temperature.

20. (a) Explain the basic operation of an full wave Precision rectifier.
(b) The circuit shown in Fig. 6, R1 = 100Ω, R2 = 56kΩ, Vi = 1Vpp sine wave, and the op-amp is type 741C
with supply voltages = ±15V. Determine the upper and lower threshold voltages and draw the
output waveform.
 Fig. 6

21. (a) With appropriate circuit diagram derive the output expression for an instrumentation amplifier.
Explain its advantages over an ordinary difference amplifier.
(b) The problems of conventional full wave rectifier are solved using precision rectifier: explain with
proper example.

22. (a) Draw the circuit diagram of a zero crossing detector. Explain its operation. Draw the input output
waveform.
(b) Perform the DC analysis of a basic differential amplifier circuit and derive expressions for the
quiescent current and output voltage.

23. (a) Implement a circuit that can perform (i) subtraction (ii) differention and derive the input-output
relationship.
(b) Derive the expression of output voltage for an inverting adder circuit using operational amplifier.

24. (a) Describe the operation of a log amplifier using an operational amplifier. Derive the expression for
the output voltage.
(b) Implement a function generator which can produce a sine wave, a square wave and a triangular
wave with the help of a block diagram. Show the circuit diagram of each block used for the
implementation.

25. (a) Explain the basic operation of an half wave Precision rectifier.
(b) Explain the operation of a Schmitt trigger circuit with the help of a circuit diagram and voltage
transfer characteristics. What is hysteresis and how does it help in elimination of noise?

26. (a) Draw the circuit diagram and explain the operation of a Monostable Multivibrator using a 555
timer IC. Derive the expression of output pulse width.
(b) In the Astable Multivibrator of the circuit shown in the Fig. 7, R1 = 6.8kΩ, R2=3.3kΩ, C=0.1µF and
C1=0.01µF. Determine the positive pulse width T1, negative pulse width T2, free-running
frequency f0, and percentage of duty cycle.
 Fig. 7

27. (a) Show that the efficiency of an RC-coupled class-A amplifier can not exceed 25%.
(b) What is cross over distortion and how it can be overcome?

28. (a) Design an automatic smoke alarm system using 555 timer IC. The circuit will be triggered by an
external signal initial alarm. The alarm rings for 1 minute and turn off.
(b) Explain the operation of a class-B amplifier and hence prove that the maximum efficiency in class-
B configuration can’t exceed 78.5%.

29. (a) Explain the working principles of Class A, Class B, and Class AB amplifiers. Compare their
operating points and conduction angles with the help of appropriate diagrams.

(b) Discuss the advantages and disadvantages of each amplifier class in terms of efficiency, linearity,
and distortion.

30. (a) Derive the expressions for calculating the DC power and AC output power of a Class B amplifier.
Explain how to calculate the power dissipation and efficiency of the amplifier.
(b) A Class B push-pull amplifier operates with a supply voltage of (VCC = 20V), and the load
resistance is (R L = 10 Ω). The peak output current is (I{peak} = 2A). Calculate the AC output
power, DC input power, and efficiency of the amplifier.
(c) Briefly explain how the efficiency of Class AB amplifiers compares with that of Class A and Class
B amplifiers. Why is Class AB often used in practical audio amplifiers?

31. (a) Describe the internal block diagram of the 555 Timer IC and explain the function of each block
(comparator, flip-flop, discharge transistor, and output stage).
(b) Design a 555 Timer-based astable multivibrator that generates a square wave of frequency 1 kHz
with a 60% duty cycle. Assume (C = 1 μ F ). Calculate the required resistor values 𝑅1 and 𝑅2 .

32. (a) Prove that the maximum efficiency of a power amplifier in class-B configuration cannot exceed
78.5%.
(b) Explain the working principle of a push pull amplifier with the help of a circuit diagram.

33. (a) Draw the circuit diagram and explain the operation of an astable multivibrator using a 555 timer
IC. Derive the expression for duty cycle.
(b) Determine the pulse width of a monostable multivibrator circuit having R = 20 kΩ and C=0.1µF.