## Analog Electronics 2 - Dec 2014

### Electronics & Telecomm. (Semester 4)

TOTAL MARKS: 80

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Assume data if required.

(4) Figures to the right indicate full marks.

### Solve any four:-

**1 (a)** Draw the high frequency hybrid -pi equivalent circuit of a BJT and define the various components in the model.(5 marks)
**1 (b)** Define differential and common mode gain, and differential an common mode input impedance of differential amplifiers.(5 marks)
**1 (c)** Draw the circuit diagram and derive the relationship between the output current and reference current for Wilson current source.(5 marks)
**1 (d)** Compare power BJTs and power MOSFETS. Determine the required power rating of a power BJT for the circuit given below.
(5 marks)
**1 (e)** List the characteristics of an ideal op-amp and compare with the practical ones.(5 marks)
**1 (f)** With the help of a neat circuit diagram explain the working of transistorized series regulator.(5 marks)
**2 (a)** Determine the corner frequency and maximum gain of a bipolar common-emitter circuit with an input coupling capacitor.
(10 marks)
**2 (b)** Determine the unity gain bandwidth of N-channel MOSFET with parameters K_{n}=0.25 mA/V^{2}, V_{TN}=1V, λ=0, Cgd=0.04pF, Cgs=0.2pF, V_{GS}=3V. If a 10 Ω load is connected to the output between drain and source determine the Miller capacitance and cut off frequency.(10 marks)
**3 (a)** Draw the small signal equivalent circuit of the bipolar differential amplifier. Determine its output voltage in the general form for one sided output V_{o}=A_{d}V_{d}+A_{cm}V_{cm2} and hence the expressions for differential mode gain and common mode gain.(10 marks)
**3 (b)** For the MOSFET differential amplifier, the transistor parameters are K_{n1}=K_{n2}=0.1 mA/V^{2}, K_{n3}=K_{n4}=0.3 mA/V^{2}, V_{TN}=1V for all transistors, λ=0 for M_{1}, M_{2} and M_{3} and λ=0.01 V^{-1} for M_{4}. Determine the bias current I_{Q}, output resistance of current source, differential-mode voltage gain common-mode voltage gain and CMRR for the differential amplifier.
(10 marks)
**4 (a)** Determine I_{REF} and Io for the two transistor current source. The circuit parameters are V^{+}=10V, V=0V, R_{1}=15 KΩ and transistor parameters are V_{BE}(on)=0.7V, β=75, and V_{A}=∞
(4 marks)
**4 (b)** Draw a neat diagram of a Wilson current source. Derive the relationship between the reference and bias currents.(8 marks)
**4 (c)** Draw the circuit diagram and small signal equivalent circuit for a Darlington pair configuration. Derive the expression for its input resistance and overall current gain.(8 marks)
**5 (a)** Define slew rate. With the help of waveforms shown how slew rate affects the output response of an operational amplifier to rectangular input voltage pulse. If the bias current of an op-amp is 19μA and its internal frequency compensation capacitor has a value of 30pF determine its slew rate.(8 marks)
**5 (b)** Draw the circuit diagram for a summing amplifier and determine the expression of output voltage v_{0} in terms of the input voltages v_{1}, v_{2} and v_{3} and the resistances used in the circuit. If it is desired to have v_{0}=-(3v_{1}+4v_{2}+2v_{3}) find suitable values of these resistances.(8 marks)
**5 (c)** With the help of VI characteristics of Zener diode explain the working of a Zener shunt regulator.(4 marks)
**6 (a)** With the help of a neat diagram, dc and ac load lines explain the working of a transformer coupled class A amplifier. What is the effect of the transformer coupling on the power conversion efficiency of the class A amplifier.(8 marks)
**6 (b)** List the different techniques for biasing the class AB power amplifier and explain any one them.(8 marks)
**6 (c)** Differentiate between two transistor and three transistor current sources.(4 marks)