Beijing Embedded System Key Lab
Power Amplifier Spring 2005 Beijing Embedded System Key Lab Linear/Nonlinear PA? Nonconstant envelop Constant envelop modulation
BPSK QPSK QAM GMSK FSK Nonlinear PA High Efficiency Linear PA Low Efficiency Effect of nonlinear PA on nonconstant envelop signal
Spectral Regrowth Effect of nonlinear PA on nonconstant envelop signal Spectrum at output of nonlinear PA Original Signal Spectrum Power Amplifier Efficiency
For ideal PA : The Drain Efficiency The Power Added Efficiency(PAE): The overall efficiency: Basic Amplification: Use RFC ( RF Chock) to in acommon source stage to drive the load Matching Typical PA Performance Linear and Nonlinear PA
Linear/Nonlinear distinction The fraction of the RF cycle for which the transistor conducts. Stability Consideration
Ps:Stable circle on Smith chart is the general tool Operating Power Gain Given the powergain,drawing the power gain circle,and select in the stable region. Calculate ,determine if a conjugate match is in the stable region.If its not stable,we can choose the arbitrarily,or according VSWR. Constant VSWR Circle DC Bias Selection Active bias network for a BJT
Low-noise,low-power : A Low-noise,higher power-gain : B High Output Power : C Higher output power and higher efficiency : D Power Amplifier Classes
Class A: conduction angle 360 Class B: conduction angle 180 Class AB: conduction angle >180 Class C: conduction angle