Available load power in a RF class D amplifier with a sigma-delta modulator driver

A conventional RF class D amplifier is nonlinear and is limited to constant envelope signals. By augmenting a RF class D amplifier with a sigma-delta (ΣΔ) modulator, the class of signals is extended to include time varying envelope signals. The available load power delivered by a class D amplifier depends on the spectral properties of the ΣΔ pulse train. A measure called coding efficiency is defined to quantify the spectral characteristics of the pulse train and the parameter is incorporated in class D design equations. The average pulse frequency of the ΣΔ pulse train affects switching losses in the amplifier and the average pulse frequency for a fourth order bandpass modulator is simulated. A 1W 1 GHz voltage switched class D amplifier is designed and simulated to verify the coding efficiency and average pulse frequency parameters.