Comparison of 10/20/40 GHz Quadrature VCOs for W-band FMCW Radar Systems in 90nm SiGe BiCMOS Technology

This paper presents and compares quadrature voltage-controlled oscillators (QVCOs) operating at 10, 20, and 40 GHz for use within W-band frequency-modulated continuous wave (FMCW) radar systems. The same circuit topology and a 90nm SiGe BiCMOS 9HP technology are used for each band. The QVCO employs Colpitts oscillators which are capacitively coupled in a ring structure. This passive coupling results in improved phase noise compared to active injection techniques. Each differential Colpitts subcircuit uses an AC-shorted transformer-coupled varactor structure to allow for wide continuous tuning range with low phase noise. Estimated quality factors of the tanks are 16/11/6 for the 10/20/40 GHz VCOs, where the higher Q is achieved through careful optimization of the transformer (with Q of ~35 for each band) and varactor structures. Our results show that the 10/20/40-GHz QVCOs achieve phase noises at 1-MHz offset of -122/-114/-105 dBc/Hz, continuous tuning ranges of 14%/10%/4%, and figures-of-merit of -181/-179/-174 dBc/Hz, respectively. After multiplication to 80 GHz, phase noises would be -104/-102/-98 dBc/Hz, respectively, indicating that the lower frequency design is preferable for the FMCW radar system, provided that high-performance multipliers are available. Keywords—Voltage-controlled oscillators, quadrature VCO, SiGe, BiCMOS, technology benchmarking, FMCW radar.