Dynamic Dual-Gate Bias Modulation for Linearization of a High-Efficiency Multistage PA

This paper investigates the linearization of high-efficiency multistage PAs through gate bias modulation derived from the envelope of the RF input signal. We show that separate control of the driver- and power-stage gate bias voltages allows for independent linearization of gain and phase. An iterative algorithm determines signal-dependent gate voltage functions that minimize amplitude-to-amplitude (AM/AM) and amplitude-to-phase (AM/PM) distortion, and is demonstrated on a 10-W high-efficiency X-band GaN monolithic microwave integrated circuit (MMIC) PA with a custom-designed hybrid dual-gate bias modulator. The noise power ratio (NPR) of a 5-MHz-wide signal is improved by as much as 9.4 dB compared to the PA with a static bias, without degradation in power-added efficiency (PAE) and gain. The measured average PAE improves from 19.9 % at 9.8-dB backoff by 0.8 points, with a saturated gain increase of 0.2 dB at 9.7 GHz. A long-term evolution (LTE) signal with different envelope statistics and a 10.6-dB peak-to-average power ratio (PAPR) is amplified with an adjacent channel power ratio (ACPR) improvement of up to 7.9 dB.