Code: AE05

Code: AE05 Subject: BASIC ELECTRONICS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or best alternative in the following: (2x10)

a. Space charge region around a p-n junction

(A) does not contain mobile carriers

(B) contains both free electrons and holes

(C) contains one type of mobile carriers depending on the level of doping

of the p or n regions

(D) contains electrons only as free carriers

b. The important characteristic of emitter follower is

(A) high input impedance and high output impedance

(B) high input impedance and low output impedance

(C) low input impedance and low output impedance

(D) low input impedance and high output impedance

c. In a JFET, at pinch-off voltage applied on the gate,

(A) the drain current becomes almost zero

(B) the drain current begins to decrease

(C) the drain current is almost at saturation value.

(D) the drain-to-source voltage is close to zero volts.

d. When an amplifier is provided with current series feedback, its

(A) input impedance increases and output impedance decreases

(B) input and output impedances both decrease

(C) input impedance decreases and output impedance increases

(D) input and output impedances both increase

e. The frequency of oscillation of a tuned-collector oscillator having L=30μH and C=300pF is nearly

(A) 267 kHz (B) 1677 kHz

(C) 1.68 kHz (D) 2.67 MHz

f. The open loop gain of an opamp available in the market may be around

(A) 10^–1 (B) 10

(C) 10⁵ (D) 10²

g. The control terminal (pin 5) of 555 timer IC is normally connected to ground through a capacitor (~ 0.01 μf). This is to

(A) protect the IC from inadvertant application of high voltage

(B) prevent false triggering by noise coupled onto the pin

(C) convert the trigger input to sharp pulse by differentiation

(D) suppress any negative triggering pulse

h. The value of ripple factor of a half-wave rectifier without filter is approximately

(A) 1.2 (B) 0.2

(C) 2.2 (D) 2.0

i. The three-variable Boolean expression:

(A) (B)

(C) (D)

j. The fan-out of a MOS logic gate is higher than that of TTL gates because of its

(A) low input impedance (B) high output impedance

(C) low output impedance (D) high input impedance

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Establish from first principles, the continuity equation, valid for transport of carriers in a semi-conductor. (10)

b. Find the values of collector and emitter currents in a transistor having I_CBO=3μA, and α_dc=0.98 when its base current is 60μA. (6)

Q.3 a. What are the important characteristics of a cascode amplifier? Write the circuit of cascode amplifier and determine an expression for its voltage gain in terms of its circuit parameters. (8)

+V_CC

b. The h-parameters of the transistor in the amplifier circuit shown below are: h_ie=2.2 KΩ , h_fe=52 h_oe=and h_re is negligible. The output load resistor dissipates a signal power of 9 mW. Determine the power gain of the amplifier using its equivalent circuit. The reactances of the capacitors may be neglected. (8)

Q.4 a. Write a neat sketch to shown the construction of a depletion-enhancement MOSFET and explain its operation in both the modes. (9)

b. The collector voltage of a Class B push pull amplifier with V_CC=40 Volts swings down to a minimum of 4 volts. The total power dissipation in both the transistors is 36 watts. Compute the total dc power input and conversion efficiency of the amplifier. (7)

Q.5 a. Draw the circuit of Hartley oscillator and derive an expression for its frequency of oscillation. (10)

b. The transistor in the feedback circuit shown below has β=200. Determine

(i) feedback factor, (ii) feedback ratio, (iii) voltage gain without feedback and (iv) voltage gain with feedback in the circuit. In the transistor, under the conditions of operation, V_BE may be assumed to be negligible. (6)

Q.6 a. Write the circuit of current mirror used in an opamp design and explain its operation. (8)

b. In the differential amplifier circuit shown below, the transistors have identical characteristics and their β=100. Determine the (i) output voltage (ii) the base currents and (iii) the base voltages taking into account the effect of the R_B and V_BE. Take V_BE=0.7 Volts. (8)

Q.7 a. Explain, using neat circuit diagram and waveforms, the application of timer IC555 as monostable multivibrator. (9)

b. Write the circuit diagram of a square wave generator using an opamp and explain its operation. (7)

Q.8 a. Draw the circuit of a series voltage regulator and describe its working. (9)

b. Design a series voltage regulator to supply 1A to a load at a constant voltage of 9V. The supply voltage to regulator is 15V±10%. The minimum zener current is 12mA. For the transistor to be used, assume V_BE=0.6V and β=50. (7)

Q.9 a. Obtain the minterms of the function

ƒ(A,B,C) =

and draw the K-map of the function. (4)

b. Distinguish between synchronous and asynchronous counters.

Show the logic diagram of a 3-bit UP-DOWN synchronous counter using suitable flip-flops, with parallel, carry based on NAND gates and explain its operation drawing wave diagrams. (12)