Doherty power amplifier with asymmetrical drain voltages for enhanced efficiency at 8 dB backed-off output power

Abstract

In this paper, we present a high-efficiency 300 W Doherty power amplifier (DPA) that can improve the efficiency at an 8 dB backoff from its saturated output power (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SAT</sub> ). To enhance the efficiency, asymmetrical drain voltages are supplied to a carrier amplifier and a peak amplifier in the DPA. The drain voltages and radio frequency (RF) circuit parameters of each amplifier are determined by basic load-impedance analysis. The DPA is fabricated using a push-pull laterally diffused metal oxide semiconductor (LDMOS) field-effect transistor (FET) for an ultrahigh frequency (UHF) band. The drain voltages are set to 50 V and 30 V. Measurement results using a continuous wave (CW) signal indicate a drain efficiency (η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) of 50% at a P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SAT</sub> of 55 dBm and a η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> of 48% at an 8 dB backoff from P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SAT</sub> , which means that the proposed DPA can extend the power range in which its highest efficiency is maintained. For a wideband code division multiple access (W-CDMA) signal with a peak-to-average power ratio (PAPR) of 8 dB, the measurement results indicate a η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> of 43% and an adjacent-channel leakage power ratio (ACLR) of -23 dBc at an output power of 47 dBm.