Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
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.282Medium
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.283Medium
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.284Hard
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.285Medium
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).
Q.286Hard
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.287Hard
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.288Easy
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.289Easy
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.290Medium
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.291Medium
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.292Easy
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.293Medium
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.294Easy
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.295Medium
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.296Hard
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.297Easy
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.298Hard
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.299Medium
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.
Q.300Easy
A continuous-time signal x(t) = 5cos(2πt + π/4) has a fundamental frequency of:
Answer: A
From x(t) = 5cos(2πt + π/4), ω = 2π, so f = ω/2π = 1 Hz
