A 38-GHz Sub-Harmonic I/Q Modulator Using LO Frequency Quadrupler in 65-nm CMOS

A 38 GHz modulator composed of a differential I/Q mixer and a high power frequency quadrupler in 65-nm CMOS for the 5G millimeter-wave (MMW) Tx application is presented. The 5 GHz LO feed is utilized which is compatible with the 5G sub-6 GHz system. In order to up-convert the 2 GHz IF signal to 38 GHz RF using the 5 GHz LO source, sub-harmonic mixers and frequency quadrupler are adopted. According to the measured results, the proposed modulator demonstrates a conversion gain of 2 dB and an OP 1dB of −10 dBm over 37.5-38.5 GHz with 42-mW dc power dissipation ( $P$ DC ) of the mixer and 120-mW $P$ DC of the frequency quadrupler. The modulator performs −47-dBc 8LO-to-RF isolation and better than −32-dBc IRR. Furthermore, due to the high 8LO-to-RF isolation and IRR performances, the 64-quadratic-amplitude modulation (QAM) with 1.5 Gb/s data rate is successfully demonstrated at 38 GHz. The proposed 38 GHz modulator shows potential for the sub-6 GHz and MMW coexistent 5G system.