Efficiency Analysis of a Switched-Capacitor Quadrature Power Amplifier Employing RF Pulse-Width-Modulation

Amplitude variation in a switched-capacitor Cartesian quadrature class-D PA can be achieved by scaling capacitor ratios or by employing pulse-width modulated signals to drive the class-D stages. The second approach allows for continuous amplitude control, thus avoiding the quantization noise that can result from discrete amplitude variation. The efficiency of the PWM class-D stage is analyzed in this paper. A brief comparison with discrete switched-capacitor-based amplitude control is presented.