A 38-GHz High-Speed I/Q Modulator Using Weak-Inversion Biasing Modified Gilbert-Cell Mixer

Abstract

A 90-nm CMOS I/Q modulator with low dc-power consumption, low local oscillator (LO) power requirement, and high image reject ratio (IRR) is proposed in this letter. To minimize dc-power consumption and LO power requirement, the weak-inversion biasing technique is adopted in the switching transistors and the modified Gilbert-cell mixer structure is also applied to solve the voltage headroom problem in conventional Gilbert-cell mixer. Moreover, to demonstrate high IRR, a four-way quadrature signal generator with low phase and gain imbalance is implemented. With only 28.8-mW dc consumption and 0-dBm LO driving power, this I/Q modulator performs −2 ± 1-dB conversion gain and better than −35-dBc IRR from 34 to 39 GHz at 0.5-GHz IF frequency. Furthermore, due to the high IRR performance, 16-quadratic-amplitude modulation (QAM) and 256-QAM measurements with data rate of 4 and 1.6 Gb/s are successfully demonstrated at 38 GHz.