What is the typical input impedance of a voltage follower (unity gain buffer) using an ideal op-amp?
Answer: B
An ideal op-amp has infinite input impedance. The voltage follower configuration maintains this high input impedance at the non-inverting input.
Q.82Medium
In a transimpedance amplifier used for photodiode detection, increasing feedback resistance Rf causes which effect?
Answer: B
In transimpedance configuration, gain = Rf. However, bandwidth is inversely proportional to Rf due to feedback capacitance (Cf ≈ Cp + Cin), creating a gain-bandwidth tradeoff.
Q.83Medium
For a common-gate FET amplifier, which statement is correct?
Answer: A
Common-gate configuration presents low input impedance (≈ 1/gm) and high output impedance. It provides good isolation and is useful for impedance matching.
Q.84Hard
What is the maximum theoretical efficiency of a Class AB amplifier?
Answer: C
Class AB combines Class A and Class B characteristics. Maximum efficiency approaches π/2(√2) ≈ 78.5% for Class B, but with Class A bias, typical maximum is around 88.5% under ideal conditions.
Q.85Medium
In a Schmitt trigger circuit using op-amp, the hysteresis voltage is determined by which factor?
Answer: B
Hysteresis voltage ΔV = 2Vsat × R1/(R1+R2), where Vsat is op-amp output saturation voltage. It depends on both the feedback resistor ratio and the op-amp's output swing (supply voltage).
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Q.86Hard
Which configuration minimizes the output impedance of an amplifier stage?
Answer: A
Series-shunt (voltage-series) feedback reduces output impedance by factor (1+Aβ). Other configurations either increase impedance or have minimal effect on output impedance.
Q.87Hard
In a log amplifier circuit, what is the primary source of error in practical implementations?
Answer: B
Log amplifier uses diode in feedback. Temperature changes cause Is (reverse saturation current) to vary exponentially, directly affecting the logarithmic transfer function. This is the dominant non-ideal effect.
Q.88Easy
For maximum power transfer from a source with internal resistance Rs to load RL, what should be the condition?
Answer: B
Maximum power transfer theorem states that maximum power is delivered when load impedance equals the complex conjugate of source impedance. For resistive cases, RL = Rs.
Q.89Easy
What is the input offset voltage of a typical precision op-amp (like OP07)?
Answer: C
Precision op-amps like OP07, OPA2134 are designed with input offset voltages < 1 mV. General purpose op-amps (e.g., 741) have offset voltages of 1-5 mV.
Q.90Medium
In a summing amplifier with multiple inputs, what determines the output voltage?
Answer: B
For a summing amplifier, Vout = -Rf(V1/R1 + V2/R2 + ... + Vn/Rn). Each input is weighted by Rf/Rin ratio, not just simple addition.
Q.91Medium
Which type of feedback configuration increases both input and output impedance?
Answer: D
Current-series (shunt-series) feedback increases both input impedance (series connection) and output impedance (current feedback). This is used in circuits requiring high impedances.
Q.92Easy
What is the slew rate of a standard 741 op-amp?
Answer: A
The 741 op-amp has a slew rate of approximately 0.5 V/μs. This limits the maximum output voltage change rate, causing distortion at high frequencies/amplitudes.
Q.93Medium
In a bridge amplifier circuit for sensor applications, what is the primary advantage?
Answer: B
Bridge amplifiers (like instrumentation amp derivative) reject common-mode signals while amplifying differential signals from sensors, ideal for noisy environments.
Q.94Easy
What is the gain-bandwidth product (GBW) of a typical 741 op-amp?
Answer: A
The 741 op-amp has a gain-bandwidth product of approximately 1 MHz. This means for a gain of 100 V/V, maximum usable bandwidth is ~10 kHz.
Q.95Medium
In a two-stage RC coupled amplifier, why is a coupling capacitor used between stages?
Answer: A
Coupling capacitors block DC bias from one stage to the next, preventing Q-point shifts. They allow AC signal passage while maintaining proper biasing independently in each stage.
Q.96Hard
For a bootstrapped voltage follower, what is the advantage over a standard buffer?
Answer: B
Bootstrapping increases input impedance by reducing effective base current drawn from source through capacitive feedback. This minimizes loading effects on high-impedance sources.
Q.97Easy
What is the bandwidth of a first-order low-pass filter with cutoff frequency fc = 1 kHz?
Answer: B
Bandwidth of a low-pass filter is defined by its cutoff frequency (-3dB point). At f = fc, magnitude drops to 0.707 of DC gain. Bandwidth = fc = 1 kHz.
Q.98Hard
In a Wien bridge oscillator, what is the condition for sustained oscillation?
Answer: C
For sustained oscillation: (1) Barkhausen condition: |Aβ| = 1 (unity loop gain), (2) Phase condition: ∠Aβ = 0° or 360°. In Wien bridge, gain needed ≈ 3 to compensate losses.
Q.99Medium
Which of the following statements about op-amp PSRR (Power Supply Rejection Ratio) is correct?
Answer: B
PSRR (in dB or V/V) measures how much power supply voltage variations appear at output. Higher PSRR (more negative in dB) = better rejection. PSRR varies with frequency and is crucial for low-noise applications.
