Electronics (ECE) - MCQ Practice Questions

Voltage gain AV = gm × RL. Maximum gain occurs when load resistance is much larger than the output impedance of the transistor, limited only by practical considerations.

Common base configuration has very low input impedance (typically 20-100 Ω) because the input is at the emitter which is forward biased.

Maximum power transfer theorem states that maximum power is delivered when load impedance is the complex conjugate of source impedance (ZL = ZS*).

Common emitter provides both voltage and current gain with gain values typically 100-1000. CB provides only current gain, CC provides only voltage gain close to 1.

Ideal op-amp has: infinite input impedance (Zin→∞), infinite open-loop gain (A→∞), zero output impedance (Zout→0), infinite bandwidth (BW→∞).

Non-inverting amplifier gain Av = 1 + (RF/Ri). With RF=0 (short circuit), gain=1 (unity gain buffer). As RF increases, gain increases.

For inverting amplifier, Gain = -Rf/Rin = -100k/10k = -10. The negative sign indicates 180° phase shift.

Hartley oscillator uses two inductors and one capacitor in the tank circuit. Frequency f = 1/(2π√L_eq×C) where L_eq is equivalent inductance.

Non-inverting amplifier uses negative feedback from output to inverting input, which reduces gain but improves linearity, bandwidth, and input impedance.

An ideal op-amp has zero input offset voltage, zero input bias current, infinite gain, infinite input impedance, and zero output impedance.

Gain = Vout/Vin = 5V/10mV = 500. Gain (dB) = 20 log₁₀(500) ≈ 54 dB.

P = V²/R → V = √(P×R) = √(100×8) = √800 ≈ 28.3 V RMS.

The voltage gain of a CS amplifier is Av = -gm × RD, where gm is transconductance and RD is the drain resistance. This is the fundamental relationship.

In saturation, the transistor acts almost like a closed switch with minimal voltage drop across it, resulting in very low output impedance.

The input impedance of a CE amplifier is Zin ≈ β × re, where β is current gain and re is emitter resistance (≈ VT/IE).

CMRR (dB) = 20 log(CMRR linear). Therefore, 80 = 20 log(CMRR), giving CMRR = 10^4 = 10,000.

The voltage gain of a voltage follower is Av ≈ 1 (or slightly less due to emitter resistance effects). It is used for impedance matching.

In the active region, IC = β × IB where β is the DC current gain (typically 50-300 for silicon BJTs).

Time constant τ = RC = 10×10³ × 100×10⁻⁹ = 10×10⁻⁴ = 1×10⁻³ s = 1 ms.

LM741 has a GBW product of approximately 1 MHz, which is why it's limited to low-frequency applications. Modern op-amps have higher GBW.