Design and analysis of CMOS broad-band compact high-linearity modulators for gigabit microwave/millimeter-wave applications

CMOS broad-band compact high-linearity binary phase-shift keying (BPSK) and IQ modulators are proposed and analyzed in this paper. The modulators are constructed utilizing a modified reflection-type topology with the transmission lines implemented on the thick SiO₂ layer to avoid the lossy silicon substrate. The monolithic microwave integrated circuit (MMIC) chips were fabricated using standard bulk 0.13-μm MS/RF CMOS process and demonstrated an ultracompact layout with more than 80% chip size reduction. The broadside couplers and 180° hybrid for the modulators in the CMOS process are broad-band designs with low phase/amplitude errors. The dc offset and imbalance for the proposed topology are investigated and compared with the conventional reflection-type modulators. The measured dc offset was improved by more than 10 dB. Both BPSK and IQ modulators feature a conversion loss of 13 dB, a modulation bandwidth of wider than 1 GHz, and second- and third-order spur suppressions of better than -30 dBc. The IQ modulator shows good sideband suppression with high local-oscillator suppression from 20 to 40 GHz. The modulators are also evaluated with a digital modulation signal and demonstrate excellent modulator quality and adjacent channel power ratio.