1. POWER AMPLIFIER
Class B
Class AB
Class C

2. 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

3. 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

4. Complimentary Push-Pull Circuit

5. CROSSOVER DISTORTION
DEAD BAND

6. The Ideal Class B

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

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

9. 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

10. The efficiency is

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

12. Class C Power Amplifier

13. Class AB Voltage Transfer Curve

14. Collector Currents & Output Current

15. 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.

16. Inductively Coupled Amplifier

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

18. TRANSFORMER COUPLED AMPLIFIER