Asymmetrical Sequential Load Modulated Balanced Amplifier With Composited Impedance Inverter and Reciprocal Mode for Broadband Applications

Abstract

In this paper, the design of a broadband asymmetrical sequential load modulation balanced amplifier (ASLMBA) is presented. The composited impedance inverters, which contain the intrinsic elements and the output matching networks (OMNs) of the balanced power amplifier (BPA) transistors, are inserted before the output coupler of the BPA pair. In this way, optimal matching condition of the BPA transistors can be maintained over a wide bandwidth. In addition, to ensure an optimal load modulation trajectory of the control amplifier (CA) without over-saturation, a reciprocal mode is applied to the BPA pair by elaborately changing the turn-on sequence of the sub-amplifiers, which is affected by the composited impedance inverter and the OMN of the control amplifier. It is illustrated that the proposed ASLMBA can effectively maintain high efficiency over an extended dynamic range and a wide bandwidth. As a proof of concept, a broadband ASLMBA working over 1.35-2.55 GHz is designed and measured in this work. Experimental results show that the designed ASLMBA achieves a saturation output power of 43.2-45.1 dBm with a saturation gain of 6.5-10.5 dB and a saturation drain efficiency (DE) of 57.8-77.7%. Meanwhile, the 6 dB and 10 dB back-off DEs of the designed ASLMBA are 51.3-66.6% and 47.7-68.9%, respectively.