A Novel 3-Way Dual-Band Doherty Power Amplifier for Enhanced Concurrent Operation

This article presents the architecture and design methodology for a new type of dual-band Doherty power amplifier (DB-DPA), referred to as 3-Way DB-DPA, which consists of a main amplifier for each band and an auxiliary amplifier handling both bands. The 3-Way DB-DPA improves the average drain efficiency in concurrent dual-band operation compared to the traditional 2-Way DB-DPA, by avoiding early clipping in the main amplifiers, while benefiting from load-pulling from the auxiliary power amplifier (PA). This improvement is verified in theory and simulation at the current-source reference planes and in measurement with a fabricated 1.5- and 2-GHz dual-band PA. A statistical analysis using 2-D continuous-wave (CW) signals with long-term evolution (LTE) probability distribution functions (PDFs) is performed and demonstrated an improvement in the concurrent average efficiency by 15 percentage points compared to the conventional 2-Way DB-DPA. In nonconcurrent operation, the measured CW drain efficiency in the lower band (1.5 GHz) is 82.8% at peak and 66.6% at 9.6-dB backoff, and the measured CW drain efficiency in the upper band (2.0 GHz) is 70.0% at peak and 48.4% at 9.4-dB backoff. The CW concurrent-balanced drain efficiency reaches 66.2/52.0% in the 3-Way DB-DPA at 3-/6-dB backoff. In single-band operation at 1.5/2.0 GHz, the average power and average drain efficiency after linearization by digital predistortion (DPD) are 35.1/37.4 dBm and 65.0/53.7%, respectively, for an LTE signal with 10-MHz bandwidth and 6.1-dB peak-to-average power ratio (PAPR). In concurrent operation, the 3-Way DB-DPA is driven by two 10-MHz LTE uncorrelated signals at 1.5 GHz with 6.86-dB PAPR and at 2.0 GHz with 6.26-dB PAPR, and the average total power and average concurrent drain efficiency after DPD are 37.5 dBm and 54.24%, respectively.