A 13.2-dBm, 138-GHz I/Q RF-DAC with 64-QAM and OFDM free-space constellation formation

An I/Q RF-DAC featuring two 6-bit DAC elements driven in quadrature, each with its own on-die antenna, and a total EIRP of 13.2 dBm, is demonstrated in a 45-nm SOI-CMOS technology. The 129-143-GHz carrier signal is first amplified by the 30-dB gain LO path and is directly modulated by the 12 baseband bit streams, without linear upconversion or power amplification. QPSK, 8-PSK, 16-QAM, 32-QAM, and 64-QAM single-carrier and OFDM constellations are formed in free-space, measured above the die at data rates up to 12 Gb/s, and at distances over 15 cm. The prototype consumes a total of 1.25 W, with an energy efficiency of 104 pJ/b.