BEE Analog and Digital Electronics 3 — Questions and Answers
Question 1: Which of the following correctly describes the operation of a MOSFET in the triode (ohmic) region?
- VGS < Vth
- VDS > VGS - Vth
- VDS < VGS - Vth and VGS > Vth (Correct answer)
- VGS = 0 and VDS > 0
Correct answer: VDS < VGS - Vth and VGS > Vth
The triode region requires the channel to be formed (VGS > Vth) and VDS to be small enough that the channel is not pinched off.
Question 2: The Boolean expression A·(A + B) simplifies to:
- A + B
- A·B
- A (Correct answer)
- B
Correct answer: A
By the absorption law, A·(A + B) = A·A + A·B = A + A·B = A(1 + B) = A.
Question 3: A 3-bit binary counter using T flip-flops requires T flip-flops that toggle on:
- Every clock edge for all bits
- Rising edge for LSB, every 2nd edge for middle bit, every 4th edge for MSB (Correct answer)
- Falling edge only
- Random intervals based on input data
Correct answer: Rising edge for LSB, every 2nd edge for middle bit, every 4th edge for MSB
In a ripple binary counter, the LSB toggles every clock cycle, the next bit every 2 cycles, and the MSB every 4 cycles.
Question 4: An ideal current source has:
- Zero internal resistance
- Infinite internal resistance (Correct answer)
- Resistance equal to the load
- Resistance equal to 50Ω
Correct answer: Infinite internal resistance
An ideal current source maintains constant current regardless of load, which requires infinite internal (parallel) resistance.
Question 5: In a Phase-Locked Loop (PLL), the voltage-controlled oscillator (VCO) output frequency is controlled by:
- The reference frequency directly
- An error voltage derived from the phase detector output (Correct answer)
- The power supply voltage
- An external crystal
Correct answer: An error voltage derived from the phase detector output
The phase detector produces an error voltage proportional to phase difference, which after filtering drives the VCO to lock onto the reference frequency.
Question 6: Which hazard in combinational logic circuits produces a momentary incorrect output glitch during input transitions?
- Race condition
- Static hazard (Correct answer)
- Dynamic hazard
- Fan-out hazard
Correct answer: Static hazard
A static hazard causes a brief unwanted pulse (glitch) when a circuit output should remain constant but momentarily changes during input transitions due to unequal path delays.
Question 7: The gain-bandwidth product (GBW) of an op-amp means that if the open-loop gain is 100,000 and GBW = 1 MHz, the open-loop bandwidth is:
- 1 MHz
- 10 Hz (Correct answer)
- 100 kHz
- 100 Hz
Correct answer: 10 Hz
Open-loop bandwidth = GBW / open-loop gain = 1×10⁶ / 100,000 = 10 Hz.
BEE Analog and Digital Electronics 3
Which of the following correctly describes the operation of a MOSFET in the triode (ohmic) region?