Input Phase Controlled Doherty Power Amplifier With Out-Phased Current Load Modulation for Arbitrary Output Back-Off

A tradeoff between bandwidth and back-off range is commonly found in the Doherty power amplifier (DPA). This paper proposes an input phase control mechanism together with a cooperative asymmetric out-phased current load modulation technique. The cooperative asymmetric out-phased current load modulation can extend the output back-off range (OBO). The input phase control mechanism together with modified impedance transforming load modulation networks (LMNs) is used to widen the DPA bandwidth. An input coupled-line coupler is implemented to realize this phase requirement. For demonstration purposes, a DPA with an operating frequency from 1.7 GHz to 2.9 GHz and with a 9-dB OBO range is designed and fabricated using GaN HEMT devices. Continuous-wave measurements show that the implemented DPA exhibits a drain efficiency ranging from 54.5% to 75.6% at saturation and from 41% to 50.6% at 9-dB OBO across the operating bandwidth. When excited by a 20-MHz long-term evolution (LTE) signal with a 9-dB peak-to-average power ratio (PAPR), the implemented DPA achieves average drain efficiencies of 41%-53.8% with an adjacent channel leakage ratio (ACLR) better than -48.1 dBc after digital predistortion (DPD).