DIGITAL ELECTRONICS MCQS PART 03

DIGITAL ELECTRONICS MCQS PART 03

1. Which of  the following is the fastest logic
(A)TTL    
(B) ECL
(C) CMOS    
(D) LSI
Ans: B
ECL is the fastest logic family of all logic families.
(High speeds are possible in ECL because the transistors are used in difference  amplifier configuration, in which they are never driven into saturation and thereby the storage time is eliminated.

2.If the input to T-flipflop is 100 Hz signal, the final output of the three T-flipflops in cascade is
(A) 1000 Hz    
(B) 500 Hz  
(C) 333 Hz    
(D) 12.5 Hz.
Ans: D

3. Which of  the memory is volatile memory
(A)ROM    
(B) RAM  
(C) PROM    
(D) EEPROM
Ans: B
Explanation: RAM is a volatile memory (Volatile memory means the contents of the RAM get erased as soon as the  power  goes off.)

4. -8 is equal to signed binary number    
(A) 10001000    
(B) 00001000  
(C) 10000000    
(D) 11000000
Ans: A
Explanation: 8 is equal to signed binary number 10001000

5. DeMorgan’s 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
 Ans: B

6. The digital logic family which has the lowest propagation delay time is
(A)ECL    
(B) TTL
(C) CMOS    
(D) PMOS
Ans: A
Explanation: The digital logic family which has the lowest propagation delay time is ECL (Lowest propagation delay time is possible in ECL because the transistors are used in difference amplifier configuration, in which they are never driven into saturation and thereby the storage time is eliminated).

7. The device which changes from serial data to parallel data is
(A)COUNTER    
(B) MULTIPLEXER
(C) DEMULTIPLEXER    
(D) FLIP-FLOP
Ans: C
Explanation: The device which changes from serial data to parallel data is demultiplexer. (A demultiplexer takes in data from one line and directs it to any of its N outputs depending on the status of the select inputs.)

8. A device which converts BCD to Seven Segment is called
(A)Encoder    
(B) Decoder
(C) Multiplexer    
(D) Demultiplexer
Ans: B
Explanation:  device which converts BCD to Seven Segment is called DECODER. (A decoder coverts binary words into alphanumeric characters.)

9.The access time of ROM using bipolar transistors is about
(A)1 sec    
(B) 1 msec
(C) 1 µsec    
(D) 1 nsec.
Ans: C
Explanation: The access time of ROM using bipolar transistors is about 1 µ sec.

10. 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.
Ans:  C
Explanation: The A/D converter whose conversion time is independent of the Number of bits is Parallel conversion.
(This type uses an array of comparators connected in parallel and comparators compare the input voltage at a particular ratio of the reference voltage).