Govt. Exams
Entrance Exams
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.
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.
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.
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.
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.
Trans-impedance gain = Rf = 1 MΩ. Output voltage Vout = Iin × Rf = 1 μA × 1 MΩ = 1 V
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.
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.
Source follower has voltage gain Av = gm·Rl/(1 + gm·Rl) ≈ 1 for practical cases, always less than 1. It provides high input impedance and low output impedance.
CMRR depends on the matching of transistor parameters and passive components. Mismatches in emitter resistances and transistor characteristics directly degrade CMRR.
