BEE Analog and Digital Electronics 4 — Questions and Answers
Question 1: In a binary-weighted DAC with a 4-bit input, the MSB resistor is R. What is the resistor value for the LSB?
- R
- 2R
- 8R (Correct answer)
- R/8
Correct answer: 8R
In a binary-weighted DAC, each bit's resistor doubles relative to the more significant bit, so the LSB resistor = 8R for a 4-bit DAC with MSB resistor R.
Question 2: A push-pull Class B power amplifier has crossover distortion because:
- The transistors have different current gains
- Each transistor only conducts for 180° and the 0.6–0.7V base-emitter threshold creates a dead zone near zero (Correct answer)
- The output transformer saturates near zero
- The supply voltage is too low
Correct answer: Each transistor only conducts for 180° and the 0.6–0.7V base-emitter threshold creates a dead zone near zero
Neither transistor conducts when the input is within ±0.6-0.7V of zero, creating a nonlinear dead band (crossover distortion) in the output.
Question 3: A multiplexer with 4 data inputs requires how many select lines?
- 4
- 1
- 2 (Correct answer)
- 3
Correct answer: 2
A 4-to-1 MUX requires 2 select lines because 2² = 4 unique combinations address all 4 inputs.
Question 4: In a successive approximation ADC (SAR ADC), converting a 0.7V input with a 1V reference and 3-bit resolution, the first trial bit sets:
- 000
- 011
- 100 (Correct answer)
- 110
Correct answer: 100
SAR always starts by setting the MSB to 1 (100), comparing 0.5V against 0.7V — since 0.7 > 0.5, the MSB is kept.
Question 5: Which of the following describes a key advantage of CMOS logic over NMOS logic?
- Higher operating speed at all frequencies
- Near-zero static power dissipation (Correct answer)
- Lower threshold voltage
- Simpler fabrication process
Correct answer: Near-zero static power dissipation
CMOS draws negligible static current because the pull-up (PMOS) and pull-down (NMOS) networks are never simultaneously fully on in steady state.
Question 6: The Miller effect in an inverting amplifier causes the input capacitance to appear as:
- Cf / (1 + |Av|)
- Cf · (1 + |Av|) (Correct answer)
- Cf · |Av|
- Cf alone
Correct answer: Cf · (1 + |Av|)
Miller's theorem shows that a feedback capacitor Cf across an inverting amplifier appears at the input as Cf·(1 + |Av|), significantly increasing effective input capacitance.
Question 7: A Johnson (twisted-ring) counter with 4 flip-flops produces how many unique states?
- 4
- 16
- 8 (Correct answer)
- 12
Correct answer: 8
A Johnson counter with N flip-flops generates 2N unique states, so 4 flip-flops produce 8 states.
BEE Analog and Digital Electronics 4
In a binary-weighted DAC with a 4-bit input, the MSB resistor is R.
What is the resistor value for the LSB?