Broadband Three-Stage Pseudoload Modulated Balanced Amplifier With Power Back-Off Efficiency Enhancement

This article presents a broadband three-stage pseudoload modulated balanced amplifier (P-LMBA) with enhanced power back-off efficiency. Unlike the conventional LMBAs, one of the balanced PA pairs of the proposed P-LMBA is modified to serve as the carrier amplifier, while the other one and the control amplifier (CA) are working as the peaking amplifiers. A new load combining network is designed to dynamically modulate the load impedance of the three PAs. Thus, the three PAs working in voltage saturation achieve peak efficiency at two different back-off and saturation points. This new load modulation mechanism enables the P-LMBA to greatly extend the back-off range and significantly enhance the power back-off efficiency. Based on the proposed theory, a three-stage P-LMBA operating from 1.6 to 2.0 GHz (22%) is designed and measured. Under the continuous-wave excitation, the measured 10-dB back-off, 6-dB back-off, and saturation efficiencies are 49%–62%, 52.4%–64.8%, and 65%–75%, respectively. The measured 10-dB back-off gain and saturation gain are 8.5–9.7 and 7.2–9.7 dB, respectively. When driven by a 20-MHz long-term evolution (LTE)-modulated signal with a 10.32-dB peak-to-average power ratio (PAPR), the proposed P-LMBA achieves an average efficiency of 42.8%–54.6% and the adjacent channel power ratios of −23.5 to −30.76 dBc.