CET CET Analog Electronics and Amplifiers 1 — Questions and Answers
Question 1: What is the voltage gain of a common-emitter amplifier with a collector resistance of 1 kΩ and emitter resistance of 100 Ω (emitter unbypassed)?
- 10 (Correct answer)
- 0.1
- 100
- 1000
Correct answer: 10
Voltage gain equals -Rc/Re; with 1000/100 the magnitude is 10.
Question 2: Which BJT amplifier configuration provides both voltage gain and current gain while inverting the output signal?
- Common-emitter (Correct answer)
- Common-base
- Common-collector
- Emitter-follower
Correct answer: Common-emitter
The common-emitter configuration inverts the output and provides both voltage and current gain.
Question 3: What is the primary purpose of a bypass capacitor placed in parallel with the emitter resistor in an amplifier?
- Increase AC voltage gain by shorting the emitter resistor at signal frequencies (Correct answer)
- Block DC bias current
- Increase input impedance
- Reduce power supply noise
Correct answer: Increase AC voltage gain by shorting the emitter resistor at signal frequencies
The bypass capacitor shorts the emitter resistor at AC frequencies, removing negative feedback and increasing gain.
Question 4: In a differential amplifier, what does a high Common-Mode Rejection Ratio (CMRR) indicate?
- The amplifier effectively rejects signals common to both inputs (Correct answer)
- The amplifier has high voltage gain
- The amplifier has wide bandwidth
- The amplifier has low noise figure
Correct answer: The amplifier effectively rejects signals common to both inputs
A high CMRR means the amplifier amplifies differential signals while strongly rejecting common-mode (noise) signals present on both inputs.
Question 5: What is the ideal input impedance of an operational amplifier?
- Infinite (Correct answer)
- Zero
- 50 Ω
- 600 Ω
Correct answer: Infinite
An ideal op-amp has infinite input impedance so it draws no current from the signal source.
Question 6: Which amplifier class operates with the transistor conducting for less than 180° of the input cycle, improving efficiency at the cost of high distortion?
- Class C (Correct answer)
- Class A
- Class B
- Class AB
Correct answer: Class C
Class C amplifiers conduct for less than 180° of the cycle, making them very efficient but highly non-linear, so they are used with tuned circuits.
CET CET Analog Electronics and Amplifiers 1
What is the voltage gain of a common-emitter amplifier with a collector resistance of 1 kΩ and emitter resistance of 100 Ω (emitter unbypassed)?