Broadband Sequential Load-Modulated Balanced Amplifier Using Coupler-PA Co-Design Approach

Abstract: The basic theory of the sequential load-modulated balanced amplifier (SLMBA) is introduced and the working principle of its active load modulation is analyzed in this paper. In order to further improve the performance of the SLMBA, a co-designed method of the coupler and power amplifier (PA) is proposed, which is different from the traditional design of couplers. According to the back-off point and saturation point of the SLMBA, this coupler-PA co-design approach can make the working state of the coupler and three-way PA closer to the actual situation, which improves the overall performance of the SLMBA. The maximum output power ratio of the control PA and the balance PA is then determined by the preset output power back-off (OBO) of 10 dB, and the phase compensation line is determined by the trace of the load modulation impedance of the balanced PA. In order to verify the proposed method, an SLMBA operating at 1.5–2.7 GHz (57% relative bandwidth) is designed. The layout simulation results show that its saturated output powers achieve 40.7–43.7 dBm and the small signal gains are 9.7–12.4 dB. Besides, the drain efficiencies at the saturated point and 10 dB OBO point are 52.7%–73.7% and 44.9%–59.2% respectively.

Keywords: SLMBA; broadband; coupler; co-design