POWER AMPLIFIER Class B Class AB Class C

CLASS B POWER AMPLIFIER Consists of complementary pair electronic devices One conducts for one half cycle of the input signal and the other conducts for another half of the input signal When the input is zero, both devices are off, the bias currents are zero and the output is zero. Ideal voltage gain is unity

For input larger than zero, A turn ON and supplies current to the load. For input less than zero, B turn ON and sinks current from the load

Complimentary Push-Pull Circuit

CROSSOVER DISTORTION DEAD BAND

The Ideal Class B

Maximum possible value of Vp is VCC The instantaneous power in Qn is;

The average power in Qn is Differentiating for maximum PQn with respect to Vp equal to zero gives us Maximum average power dissipation;

The average power delivered to the load is Power source supplies half sinewave of current, the average value is; The total power supplied by the two sources is

The efficiency is

Class AB Power Amplifier Small quiescent bias on each output transistor to eliminate crossover distortion

Class C Power Amplifier

Class AB Voltage Transfer Curve

Collector Currents & Output Current

Example The parameters are VDD=10V, RL=20Ω. The transistor are matched and K=0.2A/V2, VT=1V, IDQ=0.05 when vo=5V. Determine the required biasing in a MOSFET class AB output stage.

Inductively Coupled Amplifier

The maximum possible average signal power delivered to the load The possible average signal power supply by VCC The maximum possible power conversion efficiency

TRANSFORMER COUPLED AMPLIFIER