The Role of Nonlinear Cout in Continuous Class F PAs

This paper provides a comprehensive analysis of the role played by the equivalent nonlinear output capacitor (C_out), seen at the transistor’s intrinsic drain, in the efficiency of continuous class F (CCF) power amplifiers (PAs). New design equations of the CCF PA are derived to incorporate the effect of this capacitance. It is noted that the nonlinearity of C_out can impose both active and passive second harmonic terminations at the current-source reference plane (CRP). A design methodology is proposed to obtain the optimum, passive, second harmonic terminations that maximize efficiency at the load reference plane (LRP). Finally, this improved design methodology is validated with experimental tests made on a CCF PA prototype.