Govt. Exams
Entrance Exams
The voltage gain of a voltage follower is Av ≈ 1 (or slightly less due to emitter resistance effects). It is used for impedance matching.
CMRR (dB) = 20 log(CMRR linear). Therefore, 80 = 20 log(CMRR), giving CMRR = 10^4 = 10,000.
The input impedance of a CE amplifier is Zin ≈ β × re, where β is current gain and re is emitter resistance (≈ VT/IE).
In saturation, the transistor acts almost like a closed switch with minimal voltage drop across it, resulting in very low output impedance.
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.
P = V²/R → V = √(P×R) = √(100×8) = √800 ≈ 28.3 V RMS.
Gain = Vout/Vin = 5V/10mV = 500. Gain (dB) = 20 log₁₀(500) ≈ 54 dB.
An ideal op-amp has zero input offset voltage, zero input bias current, infinite gain, infinite input impedance, and zero output impedance.
Non-inverting amplifier uses negative feedback from output to inverting input, which reduces gain but improves linearity, bandwidth, and input impedance.
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.
