A 19 dBm, 15 Gbaud, 9 bit SOI CMOS Power-DAC Cell for High-Order QAM W-Band Transmitters

A mm-wave I-Q power-DAC is reported at W-band. The circuit, which is fabricated in a 45 nm SOI CMOS technology, employs a series-stacked Gilbert-cell output stage with gate finger geometry segmentation to directly modulate a 85-95 GHz carrier. The Gilbert-cell provides phase inversion and 7 bits for ASK envelope modulation, each of which can be switched at speeds up to 15 Gb/s. A ninth bit turns the entire DAC cell on and off at 15 Gb/s, as needed to create an arbitrary 15 Gbaud QAM constellation in a symmetrical 4x4 I-Q power-DAC transmitter array, with free-space power combining and antenna-level segmentation. The measured output power and PAE of the I or Q DAC cells are 19 dBm and 8.9%, respectively. Three effective bits of amplitude resolution and one phase bit are estimated from the small-signal S-parameter measurements in the 80-95 GHz range. The envelope amplitude resolution reduces to only two effective bits under saturated output power operation. The OOK bit provides over 45 dB of measured attenuation and dynamic range, relative to the peak output power.