TEDS Base-Station Power Amplifier Using Low-Noise Envelope Tracking Power Supply

Abstract

This paper demonstrates a highly linear and efficient TETRA enhanced data service (TEDS) base-station RF power amplifier (RFPA). Based on the well-known combination of an envelope tracking (ET) power supply and a linear class-A/B RFPA, adequate adjacent channel power ratio (ACPR) and wideband noise performance is shown to be enabled only by further incorporating high-bandwidth Cartesian feedback (CFB) and using a low-noise ET power supply. It is demonstrated that CFB loop bandwidth is limited by modulator/demodulator/RF path group delay to around 2 MHz in the considered setup, and that there exists a significant tradeoff between the depth of the ET and open-loop RFPA linearity, as well as overall efficiency. An empirical method for determining the permissible amount of switching ripple on the ET supply is presented, showing very good accuracy. Performance of the prototype RFPA system is verified experimentally with a 9.6-dB peak-to-average 50-kHz 16 quadrature amplitude modulation TEDS carrier, the setup providing 44-dBm (25 W) average RF output power at 400 MHz with 44% dc-to-RF efficiency state-of-the-art ACPR of less than -67 dBc, switching noise artifacts around - 85 dBc, and an overall rms error vector magnitude below 4.5%.