BEE Analog and Digital Electronics 2 — Questions and Answers
Question 1: In a common-emitter BJT amplifier, increasing the collector resistance RC while keeping other parameters fixed will:
- Decrease voltage gain
- Increase voltage gain (Correct answer)
- Have no effect on voltage gain
- Decrease input impedance
Correct answer: Increase voltage gain
Voltage gain Av = -gm·RC, so increasing RC directly increases the magnitude of voltage gain.
Question 2: Which logic gate is equivalent to an AND gate followed by a NOT gate?
- NOR
- XNOR
- NAND (Correct answer)
- XOR
Correct answer: NAND
A NAND gate produces the complement of the AND operation, making it equivalent to AND followed by NOT.
Question 3: A Schmitt trigger is primarily used to:
- Amplify high-frequency signals
- Convert sine waves to square waves with hysteresis (Correct answer)
- Generate sawtooth waveforms
- Implement frequency division
Correct answer: Convert sine waves to square waves with hysteresis
A Schmitt trigger uses hysteresis (two threshold levels) to cleanly convert noisy analog signals into digital square waves.
Question 4: In a full-wave bridge rectifier with a peak input voltage of 20V and diode forward voltage drop of 0.7V each, the peak output voltage is:
- 20V
- 19.3V
- 18.6V (Correct answer)
- 18V
Correct answer: 18.6V
Two diodes conduct simultaneously in a bridge rectifier, so peak output = 20 - 2(0.7) = 18.6V.
Question 5: A D flip-flop differs from an SR flip-flop primarily because it:
- Has two clock inputs
- Eliminates the forbidden state by tying S and R through an inverter (Correct answer)
- Can store multiple bits
- Operates without a clock signal
Correct answer: Eliminates the forbidden state by tying S and R through an inverter
Connecting an inverter between the S and R inputs ensures S and R are always complements, eliminating the invalid S=R=1 state.
Question 6: The slew rate of an op-amp limits its ability to:
- Handle DC offset voltages
- Accurately reproduce high-amplitude, high-frequency signals (Correct answer)
- Drive capacitive loads at low frequencies
- Reject common-mode signals
Correct answer: Accurately reproduce high-amplitude, high-frequency signals
Slew rate (V/μs) limits the maximum rate of output voltage change, causing distortion when large-amplitude high-frequency signals demand faster output swings.
Question 7: In a 4-bit ripple carry adder, the worst-case propagation delay occurs when:
- Adding 0000 + 0000
- Adding 0001 + 0001
- Adding 0111 + 0001 (Correct answer)
- Adding 1000 + 1000
Correct answer: Adding 0111 + 0001
0111 + 0001 forces a carry to ripple through all four stages, producing the maximum carry propagation delay.
BEE Analog and Digital Electronics 2
In a common-emitter BJT amplifier, increasing the collector resistance RC while keeping other parameters fixed will: