Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
A 3-to-8 decoder has how many output lines, and what is the number of active outputs for any single input combination?
Answer: A
A 3-to-8 decoder has 2³ = 8 output lines. For any valid input combination, exactly 1 output line is activated (HIGH), while others remain LOW
Q.44Easy
In VHDL, what does the 'rising_edge' function detect?
Answer: B
'rising_edge' detects a transition from LOW (0) to HIGH (1) on a signal, commonly used in synchronous designs to trigger actions on positive clock edges
Q.45Easy
Which of the following is NOT a characteristic of ROM (Read-Only Memory)?
Answer: B
Standard ROM is programmed during manufacturing and cannot be reprogrammed by users. PROM, EPROM, and EEPROM allow user programming, but basic ROM does not
Q.46Easy
In a 16×4 RAM, what do the numbers 16 and 4 represent respectively?
Answer: D
16×4 RAM means 16 memory words (locations), each storing 4 bits of data. This requires log₂(16)=4 address lines. Total capacity = 16 words × 4 bits = 64 bits
Q.47Easy
What is the fundamental difference between combinational and sequential circuits?
Answer: B
Combinational circuits: output = f(present inputs only). Sequential circuits: output depends on present inputs AND past states (memory elements like flip-flops store history)
Q.48Easy
Which of the following is a characteristic of asynchronous counters?
Answer: B
Asynchronous (ripple) counters work by cascading flip-flops where the output of one flip-flop triggers the next, creating a ripple effect.
Q.49Easy
A BCD counter counts from 0 to 9 and then resets. How many flip-flops are minimum required?
Answer: C
BCD (Binary Coded Decimal) requires 4 bits to represent decimal digits 0-9 (2^4 = 16 combinations, but only 10 are used).
Q.50Easy
In a multiplexer (MUX) with 3 select lines, how many input lines can it handle?
Answer: C
A multiplexer with n select lines can handle 2^n input lines. For 3 select lines: 2^3 = 8 input lines.
Q.51Easy
A demultiplexer (DEMUX) with 4 select lines has how many output lines?
Answer: C
A demultiplexer with n select lines has 2^n output lines. For 4 select lines: 2^4 = 16 output lines.
Q.52Easy
Which type of flip-flop has the simplest truth table and is used for frequency division?
Answer: B
A T flip-flop toggles its output when T=1 and holds when T=0, making it ideal for frequency division and counter design.
Q.53Easy
Which of the following is a volatile memory?
Answer: C
RAM (Random Access Memory) is volatile and loses all data when power is removed. ROM, EPROM, and Flash memory are non-volatile.
Q.54Easy
Which of the following is a sequential circuit?
Answer: C
Sequential circuits have memory elements (flip-flops) and their output depends on past inputs. Flip-flops are the basic sequential elements; multiplexers, encoders, and decoders are combinational circuits.
Q.55Easy
In state machine design, if a machine has 15 different states, the minimum number of flip-flops needed is?
Answer: B
To represent 15 states, we need n flip-flops such that 2^n ≥ 15. Since 2^4 = 16 ≥ 15, minimum 4 flip-flops are required.
Q.56Easy
In a 3-to-8 decoder, if the binary input is 101, which output line will be activated?
Answer: A
Binary 101 = 5 in decimal, so output line 5 is activated in a decoder.
Q.57Easy
Which of the following logic gates has an output of 1 only when both inputs are different?
Answer: A
XOR (Exclusive OR) produces 1 when inputs are different and 0 when they are same.
Q.58Easy
What is the Boolean expression for a 2-input NAND gate?
Answer: B
NAND gate is the complement of AND, so Y = (A.B)' where . represents AND operation.
Q.59Easy
In a Multiplexer (MUX), how many select lines are required for an 8:1 MUX?
Answer: B
For 2^n inputs, n select lines are needed. For 8 inputs, log₂(8) = 3 select lines.
Q.60Easy
What is the primary purpose of using parity bits in error detection?
Answer: B
Parity bits are used for error detection by tracking whether the number of 1s in data is even or odd.
