RF current mode class-D power amplifiers under periodic and non-periodic switching conditions

Analyzing a switch mode circuit under periodic excitations with variable duty cycle provides a way to predict how power efficiency varies with output power. The analysis with periodic signals mimics the behaviour of amplifying more complex non-periodic pulse encoded signals such as sigma-delta modulation (SDM). Equations are derived to predict the power efficiency of a RF current mode class-D (CMCD) amplifier design. New results are presented that include the effect of switch capacitance and the analysis shows, that at low power, the capacitive switching losses can exceed inductive switching losses. The predictions of the model are compared with simulations of a CMCD amplifier under periodic and SDM switching conditions. The CMCD amplifier uses a large signal device model for a Cree 15 W GaN power device at a frequency of 1 GHz.