Anna University Chennai B.E Electronics & Communication Engineering EC1201-Electron Devices B.E/Electronics and Communication Engineering, May/ June 2010, Third Semester Question paper

B.E/B.tech. Degree Examinations, May/June 2010
Third semester
Electronics and Communication Engineering
EC 1201 - Electron Devices
(Regulations 2007)
Time :Three hours maximum: 100 Marks

Part A:

1. Define electric field intensity.
2. Denote the expression for force acting on a conductor kept in a magnetic field.
3. What is a Varactor diode and give two applications for it?
4. Distinguish between Avalanche break down and zener break down.
5. The common base DC current gain of a transistor is 0.967. If the emitter is 10mA, what is the value of base current?
6. What is thermal runaway?
7. What are the precautions that should be followed to handle the mosfet?
9. What is LASCR?
10. What is the major demerit of conventional thyristor?

Part b:

11 (a) (i). Two plane parallel plates 'A' and 'B' are placed 3mm apart and potential of B is made 200v positive with respect to plate A. An electron starts from rest from plate A. Calculate (1) the velocity of the electron on reaching plate B, (2) time taken by the electron to travel from plate A to plate B, and (3) kinetic energy of the electron on reaching the plate B. (6 marks)
(ii) Describe in detail about motion of an electron in magnetic field.

(or)

(b) Discuss in detail about electro static and magnetic deflection in Cathode Ray Tube.

12 (a) (i). Write a brief note on drift and diffusion current.
(ii) Explain in detail about tunnel diode.

(or)

(b) (i) Describe in detail about junction diode switching characteristics.
(ii) The reverse saturation current of a silicon PN junction diode is 10uA. Calculate the diode current for the forward-bias voltage of 0.6 v and 298 degree kelvin. The 'nu' value of silicon is 2.

13 (a) (i) Draw the self or emitter bias circuit for a common emitter amplifier and derive its stability factor.
(ii) A silicon transistor whose beta is 100 is configured in fixed bias with the following specifications : Vcc=6v, Rc=3Kohm and Rb=530KOhm. Draw the dc load line and determine the operating point. What is the stability factor?

(or)

(b) Draw the hybrid model of a transistor amplifier circuit using h-parameters and derive the expression for current gain, input impedance, Voltage gain and output admittance.

14 (a) (i) Derive the expression that relates the transconductance (gm) and saturation drain current(Idss).
(ii) Write a detailed note on enhancement MOSFET.

(or)

(b) (i) Distinguish between N-channel MOSFET and P-Channel MOSFET.
(ii) Distinguish between MOSFET and JFET.

15 (a) Explain the following with neat schematic diagram (i) SCR (ii) TRIAC

(or)

(b) Write a detailed note on : (i) Schottky Barrier Diode (ii) UJT