*8231*

8231

(Pages : 4)

Reg. No. : .................................... Name : .........................................

Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) Branch : Applied Electronics & Instrumentation 08.305 : FUNCTIONAL ELECTRONICS (A) Time : 3 Hours

Max. Marks : 100 PART â€“ A

Answer all questions. 1. Derive expression for pulse width of a monostable multivibrator. 2. Draw and explain the hysteresis curve of a Schmitt trigger. 3. The transistor circuit shown in figure is having Î˛ in the range 50 to 150. Find the value of RB that results in saturation with an overdrive factor of atleast 10.

4. What is the impact of body effect on the small signal equivalent circuit of MOSFET ? 5. Explain Miller effect. P.T.O .

8231

-2-

*8231*

W = 4 mA V2 and Vt = – 2V. L Neglecting the effect of VDS and iD in the saturation region, find the voltage that will appear at the source terminal.

6. The depletion type MOSFET shown in figure has K′n

7 Explain how negative feedback stabilizes gain. 8. For the circuit shown, determine the small signal voltage gain. The transistor parameters are VTN = 0.8V, Kn = 1 mA/V2 and λ = 0.

*8231*

-3-

8231

9. An amplifier without feedback has a transfer gain of –2000 and gain change of 15% due to temperature. Calculate the change in gain if negative feedback is given with β = – 0.02. 10. For a class B power amplifier providing a 20 V signal to a 16 Ω load and power supply of 35 V. Determine the input power, output power and circuit efficiency. (10×4=40 Marks) PART – B Answer any two questions from each Module. MODULE – I 11. Using small signal analysis derive expression for voltage gain, input impedance and output impedance of a CE amplifier.

12. a)

For the bias circuit shown in Fig., find the coordinates of Q- point. Draw DC load line and locate Q-point. Assume silicon transistor with VBE = 0.7 V. b) What is thermal runaway ?

8231

*8231*

-4-

13. Consider an n-channel enhancement mode MOSFET with the following parameters. VTN = 0.75 V, W = 40 μ m, L = 4 μ m μ

n

= 650 cm2/V–S, tox = 450Å, and

∈ox = ( 3.9) (8.85 × 10 −14 ) F cm . Determine the current when VGS = 2 VTN, for the transistor biased in saturation region. (2×10=20 Marks)

MODULE – II 14. Draw the small signal equivalent circuit of a source follower and derive expression for Av and Ro 15. For an n-channel MOSFET, the parameters are Kn = 0.2 mA/V2, VTN = 1 V, λ = 0. Cgd = 0.02 pF, Cgs = 0.25 pF. The device is biased at I DQ = 0.4 mA. Determine the unity gain frequency. 16. An enhancement type MOSFET with K′n

W = 0.2 mA V 2 , V T = 1.5 V and L

λ = 0.02 V–1 is operated at V = 3.5 V. Find the drain current obtained at V = 2V. GS DS

Determine the output resistance r0 at this value of VGS.

(2×10=20 Marks)

MODULE – III 17. With circuit schematic explain the working of class B push pull power amplifier. Derive expression for conversion efficiency. 18. An amplifier without feedback gives a fundamental output of 36 V with 7% second harmonic distortion when the input is 0.028 V. a) What is the output voltage if 1.2% of the output is feedback into the input in a negative voltage series feedback circuit. b) What is the input voltage if the fundamental output is maintained at 36 V but the second harmonic distortion is reduced to 1%. 19. A class B transformer coupled push pull power amplifier is to supply 5W to a 18 Ω load at VCC = 30 V. Assume transformer efficiency of 75%. Determine : a) turns ratio of the output transformer. b) power dissipation in each transistor. (2×10=20 Marks)

c) conversion efficiency. _____________