Drain Voltage Impact on a Doherty Power Amplifier's Optimal Splitting Parameters

Switching the Drain voltage $V_{dd}$ of a power amplifier (PA) in a quasi-static manner is an effective way of achieving efficient operation at a reduced aver-age output power. This work investigates the impact of $V_{dd}$ on the optimal drive function parameters of a GaN-on-Si dual-input Doherty power amplifier (di-DPA). Measurement sweeps were conducted on the frequency, power ratio, relative phase, and Gate bias setting of the Auxiliary PA for two distinct values of $V_{dd}$. A predis-torted 20-MHz signal is applied and adjusted to a fixed average output power. A quasi-static drive function is used, meaning the parameters are not dynamically modulated over power. The goal is to find an optimum set of drive parameters for each $V_{dd}$. It is demonstrated that the optimum set of drive parameters does not vary significantly over the frequency. Switching $V_{dd}$ results in a shift of the operating state of the di-DPA away from the efficiency maximum, which can be compensated for by adjustina the relative drive phase.