## Analog Electronics 2 - May 2013

### 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.
**1** Design two stage cascaded amplifier to meet the following specifications:

A_{v} ≥ 600, Ri ≥ 1MΩ, S_{ico} ≤ 10, f_{L} = 20Hz, Vo = 3V.

What would be the voltage gain for designing the circuit if both bypass capacitors are removed? To design, use suitable transistor from data sheet.(20 marks)
**2 (a)** Design a class B push-pull amplifier with appropriate biasing to minimize cross over distortion and using transformer coupling ratio for 8W of power. Use 12V DC supply. Assume R_{L} = 5Ω. For designing circuit find efficiency at full load. (15 marks)
**2 (b)** A BJJ has gm = 38m℧, rb^{'}e = 5.9 kΩ, h_{ie} = 6kΩ, rbb' = 100Ω, Cb'c = 12 pF, cb'e = 63 pf and h_{fe} = 224 and 1 KHz. Calculate α and β cut-off frequencies and f_{T}.(5 marks)
**3 (a)** Explain Millers theorem.(5 marks)
**3 (b)** For a cascaded amplifier, show that the overall lower 3db freq F_{LT} and higher 3dB frequency F_{H} with n stages. Where

and (10 marks)
**3 (c) ** Determine the maximum safe power dissipation in a transistor if the rated power is 25W, maximum junction temperature T_{jmax} = 125^{?}C. The transistor is mounted on a heat sink with ?_{cs} = 1^{?}C/W and ?_{sa} = 5^{?}C/W. (5 marks)
**4 (a)** From the circuit determine value of resistors R_{e} and R_{1}, such that the operating point I_{cq} = 10V and V_{ceq} = 10V.

Given value of R_{2} = 10K, β =100 and V_{BE} = 0.7V

(10 marks)
**4 (b)** Draw the circuit of Darlington configuration and obtain expression for current gain and input resistance. Also explain the principle of Bootstrapping with the help of appropriate diagram.(10 marks)
**5 (a)** From the given circuit, V_{BE} = 0.6, β_{ac} = β_{dc} = 100

find (1)Q point (2)Ad (3)Ac (4)CMRR (8 marks)
**5 (b)** Derive the expression for R_{if} and R<subof< sub=""> using equivalent circuit for -

(i) Voltage series negative feedback.

(ii) Current shunt negative feedback.</subof<><>(12 marks)
**6 (a)** Explain Barkhausen's criteria. Also derive the expression for frequency of oscillation of Wein Bridge Oscillator.(10 marks)
**6 (b)(i)** Write short note on: Colpitt's Oscillator.(5 marks)
**6 (b)(ii)** Write short note on: Clapp Oscillator.(5 marks)
**7(a)** For the above circuit, compute voltage levels ad sketch the waveform of voltages at B_{1}, C_{2} and B_{2}, C_{2} for permanent state and quasi stable state.

Use silicon transistors with r_{bb} = 100Ω and h_{FE} = 30(10 marks)
**7(b)** Explain the various negative feedback topologies.(10 marks)