Power Amplifiers Class B, AB,C (CMOS 0.35um,0.18um) Imran Khan

Contents Introduction Class AB,B,C Results Conclusion

Power Amplifiers Introduction  BFL (choke inductor) has a large value in order to provide an approx. constant current.  V dd is fixed for every technology  V in is the input voltage to be amplified  Linearity Ideal PA is linear but other PAs are linear in certain limits  Efficiency Normally 30% to 80% Efficiency=P out /P in

Power Amplifiers Introduction  Gain (voltage, current, power gain) magnitude of the output signal (Xo) over the magnitude of the input signal (Xi), G= Xo/Xi  Region of Operation The region of operation of MOSFET is:

Power Amplifiers Amplifier Classes  Class A Efficiency: (10-20)%, theory 50% Linearity: good, Cond. Cycle: 360º  Class B Efficiency: (35-50)%, theory 78 % Linearity: <A, Cond. Cycle: 180º  Class AB Efficiency: compromise between A& B Linearity: between A and B, Cond. Cycle: 181º-359º  Class C Efficiency: (50-60)% max 90% Linearity: worst, Cond. Cycle:<180 Current Flowing The red indicates how much of the drain current is flowing through one wave cycle.

Results- Class B (0.18um) W=375um Vlow=0.39 V

Results- Class B (0.18um)

Results- Class AB (0.18um) W=90um Vlow=0.35um

Results- Class AB (0.18um)

Results- Class C (0.18um) W=950um Vlow=0.1V

Results- Class C (0.18um)

Results- Class B (0.35um) W=1250um Vlow=0.1V

Results- Class B (0.35um)

W=350um Vlow=0.6V Results- Class AB (0.35um)

Results- Class C (0.35um) W=2.5mm Vlow=0V

Results- Class C (0.35um)

Conclusion Except class A, all PA can be used in Rf systems PA is the last element in transmission chain therefore requires most attention.