Broadband CMOS Schottky-Diode Star Mixer Using Coupled-CPW Marchand Dual-Baluns

A broadband CMOS Marchand dual-balun using stacked broadside couplers for low odd-mode impedance with surrounded ground planes for high even-mode impedance is employed to achieve a high coupling coefficient needed for a Marchand dual-balun. The demonstrated Marchand dual-balun using 0.18- $\mu \text{m}$ CMOS technology is designed at 30-GHz center frequency with an insertion loss of 11.5- and 10-dB input return loss bandwidth of over 120%. The bandwidth of 1-dB amplitude imbalance and 10° phase difference are over 100%. A broadband CMOS Schottky-diode star mixer is implemented with two Marchand dual-baluns at RF and local oscillator (LO) ports. As a result, the Schottky-diode star mixer shows conversion loss of 14 dB, LO-to-RF isolation of 26 dB, LO-to-IF isolation of 45 dB, and RF-to-IF isolation of 42 dB within 27-GHz operating bandwidth, respectively.