Broadband Symmetric Doherty Power Amplifier With Enhanced Back-Off Range Using Multiparameters Optimization Method

A novel design approach is presented to extend the bandwidth and output power back-off (OBO) range of symmetric Doherty power amplifier. The traditional single variable regulation techniques are effective for output power back-off range extension only at single frequency points. Firstly, one phase dispersion (PD factor) is introduced to characterize the OBO range versus frequency. Secondly, multi-parameters optimization of PD factor, complex combining load (CCL), and out-phased current combining (OCC) is used to alleviate the conflict of bandwidth and OBO range. Dynamically optimizing frequencydependent CCL and OCC parameters to counteract the dispersion effect of the matching network thus enable the wideband OBO extension and expanding design flexibility of symmetric DPA. For demonstration, a symmetric DPA with 9dB OBO range is proposed with a fractional operation bandwidth of 36% within 1.8-2.6 GHz. Under the continuous-wave excitation, the fabricated DPA features a 9-dB output back-off (OBO) efficiency of 37.9%– 55% and a saturated efficiency of 55.7%–66.9%, respectively. When driven by a 20-MHz long-term evolution (LTE) modulated signal with 9-dB peak-to-average ratio (PAPR), the adjacent channel power ratio (ACPR) of the fabricated DPA is better than -50.1 dBc after digital predistortion.