A 19-dBm, 15-Gbaud, 9-bit SOI CMOS power-DAC cell for high-order QAM W-band transmitters

A mm-wave IQ power-DAC is reported at W-band. The circuit, which is fabricated in a 45-nm SOI CMOS technology, employs a novel series-stacked Gilbert-cell output stage with gate finger segmentation to directly modulate an 80-95 GHz carrier in amplitude and phase with 8 bits of resolution. Each bit can be switched up to at least 15 Gb/s for an aggregate data rate of 120 Gb/s. A 9-th bit turns the DAC cell on and off at 15 Gb/s, as needed to create an arbitrary 15-Gbaud QAM constellation in a 1-W, 16-cell arrayed I-Q DAC transmitter with free-space power combining and 4-bit antenna-level segmentation. The measured gain, output power, and PAE of each DAC cell are 36 dB, 19 dBm, and 8.9%, respectively. The 8 bits of resolution in each DAC cell are necessary for spectral shaping, pre-distortion, as well as to combat non-idealities in the target 64-QAM digital transmitter.