A two-phase switching hybrid supply modulator for polar transmitters with 9% efficiency improvement
Emerging polar transmitters for highly efficient and linear power amplifiers (PAs) demand for high-efficiency, high-bandwidth and low-ripple supply modulators. In [1], a linear regulator is used; however, its efficiency is low at low power levels. A switched-mode power supply (SMPS) is used in [2]; but the high switching loss due to high switching frequency (necessary for high bandwidth) limits the maximum efficiency to ∼76%. A hybrid amplifier (HA) topology combining both linear amplifier (LA) and switching amplifier (SA) is used in some recent work [3, 4]. In this topology, a high-bandwidth LA replicates the input envelope voltage Vin at its output Vo; while the high-efficiency SA supplies most of the load current within its bandwidth. Yet, the tracking bandwidth is finite in [3]; and the LA in [4] needs to supply most of the high-frequency load current due to the exceptionally large inductor (20µH) used for realizing small output ripple; and therefore, limiting the dynamic efficiency. Figure 10.1.1 shows the proposed wideband HA featuring two-phase switching (2PHSW) for reducing ripple and improving static efficiency, and a feedforward bandpass filter (FF-BBF) for enhancing dynamic efficiency.