Bhavnagar University 2007 B.Sc Computer Technology ELECTRONIC SYSTEM DESIGN - Question Paper

ELECTRONIC SYSTEM DESIGN



Time: three hrs
Max Marks: 70

First ques. is Compulsory

ans any 4 from the remaining ques.

All ques. carry equal marks

ans all parts of any ques. at 1 place

1. ans the subsequent (7x2=14)
(a) Distinguish ranging from “transistion capacitance” and “diffusion capacitance” of a PN junction diode.
(b) Sketch the symbol and V-I characteristics of a varactor diode. List its applications.
(c) What is early effect in a BJT?
(d) A BJT has I8 = 10 µA, ß° =99 and IB=20 µA What is its IC and IE ?
(e) Name the parameters that are responsible for the shift in the operating point of a BJT amplifier with temperature. provide the variation of these parameters with temperature.
(f) Sketch the output and transfer characteristics of an enhancement MOSFET.
(g) In a half wave rectifier circuit, the transformer has a secondary voltage of 184 V r.m.s. The PIV rating of the diode is 250 V. discuss whether the diode can be used in this circuit.


2. (a) Differentiate ranging from drift current and diffusion currents. explain in details the different current components in a i) forward biased PN junction in diode and ii) reverse biased PN junction diode.

(b) Sketch the V-I characteristics of a PN junction diode and discuss how they vary with temperature.

(c) An ideal Ge PN junction diode has a reverse saturation current of 10 µA at 300° K. obtain the static and dynamic resistance of the diode at a forward bias of 0.2 V and at 360° K.

3. (a) What is tunneling in a tunnel diode?
discuss the V-I characteristics of a Tunnel diode with the help of its energy band diagrams. List its applications.

(b) Show the 2 transistor analogous circuit of a SCR and discuss its operation. Sketch its V-I characteristics. explain its turn-ON and turn-OFF mechanisms.

4. (a) Sketch the profiles of the currents entering (or leaving) the base region in an NPN transistor in active biased condition and hence discuss the operation of the transistor.

(b) For the circuit shown in below, determine, IC and VCE. presume for BJT ß°=99 and VBE0 V.

-----DIAGRAM-----

5. (a) discuss the reasons for shift in the operating point of a BJT amplifier with temperature. define briefly the bias stabilization circuits used.

(b) Design a shelf bias (emitter bias) circuit for an CE amplifier using a BIT having ßo = 99 and VBE=0V. The desired operating point is VCE=4V and IC=2mA. presume VCC =10 V and Rc =2KO and S=8. Show the circuit with all the component values.

6. (a) discuss why a IFET is called a umpolar device. define its operation with a neat sketch and its input and transfer characteristics. What is punch off voltage and mark it on the characteristics?

(b) Deduce the small signal equivalent circuit for a IFET and prove that gm = 2/l VP l vIDSS.IDS

(c) AJFET has Vp = -4V, IDSS =12 mA and IDS =3 mA. What is its ‘Vas’ and ‘gm’?

7. (a) Draw the circuit diagram of a bridge rectifier with a capacitor input filter and discuss its operation with waveforms. Derive the expressions for its output d.c. voltage and ripple voltage.

(b) A 50 Hz., bridge rectifier power supply is needed to give a d.c. voltage of 100 volts to a load of five kilo ohms. The minimum r.m.s. ripple voltage is to be 500 mV. obtain the minimum value of the capacitance C needed and the r.m.s. value of the secondary voltage of the secondary voltage of the transformer.

8. (a) discuss with a neat circuit diagram how a zener diode can be used as a voltage regulator.

(b) For the CE amplifier circuit shown in below, determine:
(i) the mid-band voltage gain Vo/Vs and (ii) the lower 3-dB cut off frequency ‘fz’. presume for BJT hre =0 and hoe =25 µ A/V as parameters.

Earning:   Approval pending.