Gate Bias Adaptation of Doherty Power Amplifier for High Efficiency and High Power

Abstract

This letter presents an approach to maximize the output power and efficiency of a Doherty power amplifier (PA). The conventional carrier PA having match, used in a symmetric Doherty PA, does not deliver the saturated high efficiency at the 6 dB back-off power but at the 5.5 dB back-off power due to the knee voltage effect. To solve the problem, the gate biases of the carrier and peaking PAs are adapted. The gate bias voltage of the carrier PA is optimized for a higher peak output power, delivering a 3 dB larger peak power at match. That of the peaking PA is also optimized to have the same peak power of the carrier PA. A Doherty PA with the concept is designed using a 45 W gallium nitride (GaN) high electron mobility transistors (HEMT) for the carrier and peaking cells at 1.94 GHz. The measured average output power, drain/power-added efficiencies and gain are 44.35 dBm, 60.5/57.2%, and 12.75 dB for a 10 MHz long term evolution (LTE) signal with a 6.5 dB peak-to-average power ratio (PAPR). Index Terms-Drain efficiency (DE), Gallium nitride (GaN), long term evolution (LTE), power amplifier (PA).

High efficiency Doherty power amplifiers for modern wireless communication systems: A brief review

“…The measured results show high efficiency, over 62% at 6 dB BO. The work of [27] optimized the carrier's offset line to compensate for phase mismatch at the BO associated with conventional DPA. The characteristic impedances of the carrier's offset line and impedance inverter are set to R 0 /2, which is the same load impedance at the BO, instead of R 0 in conventional DPAs.…”

Asymmetric Doherty Power Amplifier with Input Phase/Power Adjustment and Envelope Tracking

“…Envelop tracking (ET) is also developed for main or auxiliary PA in order to significantly improve the efficiency during the wide input power range [33,34]. The turn-on time of the auxiliary amplifier can be controlled by the gate bias variation as well, which always cooperates with the power ratio adjustment method [35][36][37].…”

“…Envelop tracking (ET) is also developed for main or auxiliary PA in order to significantly improve the efficiency during the wide input power range [33,34]. The turn-on time of the auxiliary amplifier can be controlled by the gate bias variation as well, which always cooperates with the power ratio adjustment method [35][36][37]. To mainly address the issue of the efficiency enhancement in the wide power dynamic range, we experimentally demonstrate an asymmetrical DPA with ET of the auxiliary amplifier in this paper, in order to keep a high efficiency over a wider range of output powers compared to classical Doherty designs.…”

Design of Broadband Doherty Power Amplifier Based on Misaligned Current Phase

“…Though the bandwidth of a DPA can be extended through so many advanced design methods, efficiency degradation can always be observed in the high-power region. There are some innovative works that have been conducted to address this problem [34][35][36]. In [34], an adaptive technique was adopted in the carrier and peaking PAs to dynamically tune the gate voltage, enhancing the efficiency of the DPA.…”