Code: D-09 Subject: DIGITAL ELECTRONICS

Time: 3 Hours Max. Marks: 100

NOTE: There are 11 Questions in all.

Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.

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

Q.1 Choose the correct or best alternative in the following: (2x8)

a. 8 is equal to signed binary number

(A) 10001000. (B) 00001000.

(C) 10000000. (D) 11000000.

b. DeMorgans first theorem shows the equivalence of

(A) OR gate and Exclusive OR gate.

(B) NOR gate and Bubbled AND gate.

(C) NOR gate and NAND gate.

(D) NAND gate and NOT gate.

c. The digital logic family which has the lowest propagation delay time is

(A) ECL. (B) TTL.

(C) CMOS. (D) PMOS.

d. The device which changes from serial data to parallel data is

(A) COUNTER. (B) MULTIPLEXER.

(C) DEMULTIPLEXER. (D) FLIP-FLOP.

e. A device which converts BCD to Seven Segment is called

(A) Encoder. (B) Decoder.

(C) Multiplexer. (D) Demultiplexer.

f. In a JK Flip-Flop, toggle means

(A) Set Q =1 and .

(B) Set Q = 0 ad .

(C) Change the output to the opposite state.

(D) No change in output.

g. The access time of ROM using bipolar transistors is about

(A) 1 sec. (B) 1 msec.

(C) 1 (D) 1 nsec.

h. The A/D converter whose conversion time is independent of the number of bits is

(A) Dual slope. (B) Counter type.

(C) Parallel conversion. (D) Successive approximation.

PART I

Answer any THREE Questions. Each question carries 14 marks.

Q.2 a. Solve the following equations for X

(i) (ii) . (6)

b. Perform the following additions using 2s complement

(i) -20 to +26 (ii) 25 to -15 (5)

c. (i) Convert the decimal number 430 to Excess-3 code.

(ii) Convert the binary number 10110 to Gray code. (3)

Q.3 a. Verify that the following operations are commutative but not associative

(i) NAND (ii) NOR. (6)

b. Prove the following equations using the Boolean algebraic theorems:

(i)

(ii) . (5)

c. The voltage waveforms shown in Fig.1 are applied at the inputs of 2-input AND and OR gates. Determine the output waveforms. (3)

Q.4 a. A staircase light is controlled by two switches one at the top of the stairs and another at the bottom of stairs

(i) Make a truth table for this system.

(ii) Write the logic equation is SOP form.

(iii) Realize the circuit using AND-OR gates. (5)

b. Minimize the following logic function using K-maps and realize using NAND and NOR gates.

(9)

Q.5 a. What are the advantages of CMOS logic and explain CMOS Inverter with the help of a neat circuit diagram. (7)

b. What is Tri-state logic and explain Tri-state logic inverter with the help of a circuit diagram. Give its Truth Table. (7)

Q.6 a. Draw the logic diagram of Full Adder using NAND gates and explain its action with the help of truth table. (8)

b. What is a digital comparator. Explain the working of a 2-bit digital comparator with the help of Truth Table. (6)

PART II

Answer any THREE Questions. Each question carries 14 marks.

Q.7 a. Design a 4 to 1 Multiplexer by using the three variable function given by . (7)

b. Explain the working of Master-slave J-K Flip-Flop with the help of logic diagram. (7)

Q.8 a. What is a Shift Register? What are its various types? List out some applications of Shift Register. (6)

b. Design a MOD-6 synchronous counter using J-K Flip-Flops. (8)

Q.9 a. What is ROM? Is the ROM a volatile memory? Explain. (3)

b. Draw the logic diagram of 16-bit ROM Array and explain its principle of operation. (8)

c. Explain briefly, why dynamic RAMs require refreshing? (3)

Q.10 a. Draw the schematic circuit of an Analog to Digital converter using Voltage-to Frequency conversion and explain its principle of operation. Draw its relevant Waveforms. (10)

b. Find the conversion time of a Successive Approximation A/D converter which uses a 2 MHz clock and a 5-bit binary ladder containing 8V reference. What is the Conversion Rate? (4)

Q.11 a. With the help of R-2R binary ladder network, explain the working of a 3-bit D/A converter and derive an expression for the output voltage. (10)

b. A 6-bit R-2R ladder D/A Converter has a reference voltage of 6.5V. It meets

standard linearity. Find

(i) The Resolution in Percent.

(ii) The output voltage for the word 011100. (4)