There is a growing demand for broadband-cellular traffic which is the catalyst toward 5G wireless standardization for the roll-out of gigabit-per-second mm-Wave technology in the next few years. Gigabit-per-second millimeter-wave (mm-wave) access and backhaul networks at 28GHz demand high-order QAM, OFDM, and/or carrier-aggregated waveforms that force the PA to operate under high peak-to-average power ratio (PAPR). High PAPR requirements aggravate the design of mm-wave Si CMOS and SiGe BiCMOS PAs since a linear response and high efficiency are simultaneously desired. Recent work has demonstrated mm-wave PAs with peak efficiency exceeding 30% at 28GHz for output powers above 20dBm. However, high average efficiency associated with high-PAPR waveforms remains elusive. To improve average efficiency, circuit techniques based on Doherty and outphasing have been demonstrated in mm-wave bands. Earlier work using these techniques showed average efficiency with QAM waveforms that is well under 20%.
Researchers at UC San Diego have an invention that is a fully prototyped 28-GHz outphasing RF power amplifier with record average efficiency based on a low-loss Chireix combiner implemented as a planar triaxial balun in a SiGe BiCMOS process. The planar power combiner has a measured insertion loss of 0.52 dB. The PA reaches a saturated output power PSAT of 23 dBm from a supply of 4.0 V with a peak PAE of 41% at 21 dBm and a PAE of 34.7% at a 6 dB backoff. The PA transmits a 64-QAM OFDM waveform with an EVM of 3% at an average output power of 14.3 dBm and PAE of 25.3%.
It is a novel power combiner architecture that can be used for outphasing power amplifiers which can be used for both board level and integrated circuits.
A working prototype has been developed.
A provisional patent has been submitted and the technology is available for licensing.