High Power Transmitter Technologies for Ultra Wideband Multi-Function RF Operation

This research explored novel high-power transmitter architectures capable of efficiently transmitting high-order modulation schemes across multiple frequency bands. Current state-of- the-art outphasing transmitters are capable of using highly-efficient switch-mode power amplifiers to transmit waveforms by decomposing an amplitude and phase modulated signal into two constant-envelope phase modulated signals. After amplification, the signals are combined by a passive power combiner and the phase difference between the signals will lead to amplitude modulation in the combined signal (figure 1). While this has proven to be a very power efficient architecture, the two-path design limits the peak-to-average power ratio (PAPR) of the transmitter, which in turn limits the modulations schemes it is capable of transmitting. A novel four-path outphasing architecture was developed to overcome the shortcomings of the traditional two-path architecture. The architecture is capable of more efficiently transmitting higher-order modulation schemes because of the improved dynamic range of a four-way combiner. In addition, reconfigurable phase modulators were designed to allow the architecture to continually cover S, C, and lower X frequency bands (2.2-10.4 GHz). This architecture was implemented in 45nm CMOS/ 0.25um GaN technology as a part of DARPA’s Diverse Accessible Heterogeneous Integration (DAHI) process technology. The first-generation design served as a proof-of-concept that only covers half of the target frequency and has decreased phase resolution. This design has been fabricated and is currently being tested. The second-generation design, which covers the entire frequency range and features 16-bit phase resolution, has been designed and will be fabricated in December 2016.