AMIETE –CS/IT (OLD SCHEME)

Code: AC03 / AT03 Subject: BASIC ELECTRONICS &

Time: 3 Hours DIGITAL CIRCUITS

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 the best alternative in the following: (210)

a. The pentavalent impurities like antimony and phosphorous added to intrinsic semiconductors are called as

(A) acceptor or P-type impurities (B) donor or P-type impurities

(C) donor or N-type impurities (D) acceptor or N-type impurities

b. The leakage current I_CBO flows in

(A) The emitter, base and collector leads

(B) The emitter and collector leads

(C) The base and collector leads

(D) The emitter and collector leads

c. The h-parameters are called hybrid parameters because they

(A) are different from y and z parameters

(B) are mixed with other parameters

(C) apply to a general two-port system

(D) are defined by using both open circuit and short circuit terminations

d. For a common source JFET amplifier, the equation for the output voltage with usual notations is

(A) (B)

(C) (D)

with usual notations.

e. The basic purpose of a filter in a rectifier is to

(A) Minimise variations in a.c input signal

(B) Suppress harmonics in rectified output

(C) Remove ripples from the rectified output

(D) Stabilise d.c output voltage

e. In an operational amplifier SUMMER circuit of the inverting type, the inputs V₁, V₂, V₃, & V₄ are connected through a series resistance of values 1 k, 2 k, 4

k and 8 k respectively. If V₁=V₃=5 volts and V₂=1.25 volt & V₄=0 volt then for a feedback resistor of 1 k for the op-amp, the output of circuit will be equal to

(A) – 5 V (B) – 4.92 V

(C) 11.25 V (D) – 8.1 V

g. The Demorgan equivalent for a 3-input NAND gate is

(A)

	(B)

(C) (D)

h. A memory array that is used for permanent data storage is

(A) the RAM (B) the shift register

(C) the ROM (D) the static RAM cell

i. The operation of the JK Flip-Flop is said to be ‘toggle’, when the J and K inputs are:

(A) 0 and 1 (B) 1 and 0

(C) 1 and 1 (D) 0 and 0

j. PLAs are

(A) Sequential Logic devices

(B) Programmable-Sequential devices

(C) Non-minimised combinational circuit

(D) Reduced combinational circuit.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Briefly explain extrinsic semiconductors. (4)

b. What is the use of clipping circuits? For the circuit shown in the Fig.1, when a sinusoidal signal of peak amplitude greater than V_R is applied at its input. Write the shape of the output waveform. Explain the operation of the circuit using the transfer characteristic for the circuit. Do not take the cut-in voltage (knee voltage) & the forward resistance of the diode as zero. (10)

c. What do you mean by biasing of a BJT? (2)

Q.3 a. Give the detailed circuit of an R-C coupled amplifier using BJT and comment on the function of each component in the circuit. (6)

b. With neat circuit diagram of a common-source FET amplifier, explain the steps to draw its low  frequency model. Comment on the equivalent circuit in brief. (8)

c. A Hartley Oscillator is designed with L₁=2 mH and L₂=20 . If the       frequency of oscillation is 950 kHz, determine the value of capacitance  required. (2)

Q.4 a. What is an op-amp? Write the schematic of the basic operational amplifier and its low frequency equivalent circuit. Mention the characteristics of an ideal operational amplifier. (7)

b. What is a rectifier? Sketch the output ‘v_o’ and determine the dc level of the output for the network of Fig 2, assuming that the diode is ideal. Repeat the above, if the ideal diode is replaced by a silicon diode. (7)

Fig 2

c. Write a brief note on voltage regulation. (2)

Q.5 a. What is a Karnaugh map? Consider the K-map in Fig. 3. Write the simplest sum-of-products logic expression and simplest product of sum logic expression. (8)

b. What is a magnitude comparator? Write the block diagram and truth table for a

2-bit magnitude comparator and obtain its implementation using logic gates.(8)

Q.6 a. Briefly explain the transistor switching times. (6)

b. How are digital circuits employing MOSFETS categorised? Briefly mention their features. With a sketch for illustration, briefly explain an N-MOS inverter. (10)

Q.7 a. Briefly comment on the followings of a standard TTL gate: (i) Power dissipation (ii) Propagation delays (iii) Fan-out.

Write a brief note on improved performance TTL family. (7)

b. What is the advantage of ECL family over TTL family? Write the basic ECL circuit and briefly explain. (9)

Q.8 a. What is a Flip-Flop? With a sketch for illustration, briefly explain the working of a S-R clocked flip-flop. State the function of preset & clear inputs. (10)

b. What is a shift register? Write the schematic of a 5-bit shift register using flip-flops of the S-R / master-slave type. (6)

Q.9 a. What is a multiplexer? Write the symbol and truth table of a 4-to-1 multiplexer. Briefly explain the truth table. Obtain the functional table for the multiplexer. And the compression for output. (9)

b. Write a brief note on semiconductor RAM. What is a PLA? (7)