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.
In a Wien Bridge oscillator, the frequency of oscillation is determined by:
Answer: B
Wien Bridge oscillator has frequency of oscillation: f = 1/(2πRC), where R and C are the series and parallel RC components in the bridge network.
Q.122Medium
What is the phase shift introduced by a first-order RC low-pass filter at the cutoff frequency (fc)?
Answer: B
At cutoff frequency, the impedances of R and C are equal, resulting in a phase shift of -45° for a single RC low-pass filter.
Q.123Medium
A trans-impedance amplifier (TIA) has feedback resistor Rf = 1 MΩ. If the input current is 1 μA, what is the output voltage?
Answer: A
Trans-impedance gain = Rf = 1 MΩ. Output voltage Vout = Iin × Rf = 1 μA × 1 MΩ = 1 V
Q.124Medium
In a Class A amplifier operating at quiescent point Q, if the load line intersects the characteristic curve at VCE = 6V and IC = 50 mA, what is the maximum output power swing (assuming linear operation)?
Answer: B
In Class A, maximum output power = 0.5 × VCE × IC = 0.5 × 6 × 50 = 150 mW. The factor 0.5 accounts for peak AC swing being limited to half the quiescent values.
Q.125Medium
Which of the following topologies provides the highest input impedance for an amplifier?
Answer: B
Source follower (Common Drain) provides extremely high input impedance (in gigaohms range) because the gate of the FET is the input, which has very high impedance characteristic of FET gates.
Q.126Medium
In a precision rectifier (ideal diode) circuit using op-amp, what is the key advantage over conventional diode rectifiers?
Answer: A
Precision rectifier uses op-amp feedback to compensate for the forward voltage drop (Vf ≈ 0.7V) of the diode, making it ideal for low-signal applications.
Q.127Medium
A cascode amplifier configuration is preferred over single-stage amplifier because it provides:
Answer: A
Cascode configuration cascades a common-emitter/source stage with a common-base/gate stage, providing high gain while significantly reducing Miller capacitance effect and improving bandwidth.
Q.128Medium
In a Push-Pull (Class B) amplifier, what is the primary disadvantage that Class AB configuration addresses?
Answer: A
Class B exhibits crossover distortion where both transistors are off near the zero-crossing point. Class AB adds small quiescent bias to keep transistors in active region, eliminating this distortion.
Q.129Medium
In a feedback amplifier, negative feedback is applied by feeding back output to which junction?
Answer: C
Negative feedback must be applied in opposition to the input signal. For inverting topology, feedback goes to inverting terminal; for non-inverting, to non-inverting terminal. The feedback signal opposes the original input.
Q.130Medium
In a BJT differential amplifier, if both inputs are grounded and the tail current source has finite output impedance, what is the effect on CMRR?
Answer: A
Finite output impedance of tail current source reduces the symmetry of the differential pair, degrading Common Mode Rejection Ratio. Higher impedance improves CMRR.
Q.131Medium
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.132Medium
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.133Medium
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.134Medium
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.135Medium
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.136Medium
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.137Medium
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.138Medium
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.139Medium
The Fourier transform of a rectangular pulse rect(t/T) is:
Answer: A
The Fourier transform of rect(t/T) is T·sinc(πfT) where sinc(x) = sin(x)/x
Q.140Medium
A system is BIBO stable if:
Answer: B
Bounded Input Bounded Output stability requires the impulse response to be absolutely summable: ∑|h[n]| < ∞
