A 60-GHz Dual-Vector Doherty Beamformer

In this paper, we demonstrate a 60-GHz transmit beamformer implemented in 130-nm SiGe BiCMOS technology which includes a Doherty amplifier driven by a dual-vector phase rotator (DVR). In addition, a benchmarking circuit comprising another DVR followed by two class-AB amplifiers, each nearly identical to the carrier amplifier within the Doherty, is included which allows us to measure the Doherty improvement in terms of efficiency and output power over conventional approaches. The dual-vector Doherty element achieves 28-dB gain with an output 1-dB compression point of +16.7 dBm. A power-added efficiency (PAE) of 16.5% is realized at 1-dB compression, with 10.8% and 7% PAE at 3- and 6-dB back-off, respectively. A stand-alone Doherty amplifier achieves a 17.1-dBm output 1-dB compression point at 23.7% PAE and a 6-dB back-off PAE of 13%. The DVR performs the phase shifting for each phased-array element necessary for beamforming, as well as providing tunable amplitude balance and phase separation between input signals to the Doherty amplifier. This allows optimization of both linearity and efficiency profiles across frequency. The Doherty element is capable of generating full 360° phase shifts with 5-b accuracy having root-mean-squared errors less than 0.6 dB in amplitude and 6° in phase from 60 to 66 GHz.

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