Supply-Modulated GaN PAs for Broadband High-PAR Signals

Supply modulation is shown to be a possible method for efficiency enhancement of microwave RFPAs, with a variety of forms one of which is envelope tracking (ET). In order to improve overall transmitter efficiency, the supply modulator needs to be efficient. With increasing signal bandwidth and peak-to-average power ratio, the demands on the slew rate of the supply modulator increase, thus decreasing its efficiency. For IQ bandwidths in the 100MHz range, the supply modulator would need to have an approximate 1-GHz bandwidth, making efficient ET impossible with current technology. In this talk, we discuss methods to apply reduced slew rate supply modulation at much lower bandwidths to enhance efficiency of microwave GaN MMIC PAs at X-band and above, for signals with PARs of 10-13dB and bandwidths exceeding 100MHz. When such reduced-bandwidth supply modulation is implemented, the linearity suffers, and architecture-compatible linearization methods are also investigated. Examples are shown for 10-GHz 10-W 150-nm GaN MMIC PAs with 100 and 250-MHz band-limited Gaussian noise signals, with average efficiencies above 40%. Several supply modulator architectures, also implemented in 150-nm GaN, are also discussed, as well as integration and linearization approaches. Additionally, scaling to larger-bandwidth signals, multiple signals, and larger RF bandwidth PAs are discussed