Design and Analysis of a Broadband Current-Mode CMOS Direct-Conversion Receiver Frond-End Circuit

A broadband (0.8-5 GHz) CMOS current-mode direct-conversion receiver has been integrated in a 0.18-mu m CMOS process. The proposed receiver front-end features a broadband active-balun low-noise transconductance amplifier (LNTA) driving a current-mode passive mixer terminated by a low-input-impedance transimpedance amplifier (TIA). The receiver chain has improved robustness to out-of-band interference, conversion gain and outstanding linearity. With the technique of noise and distortion cancellation which performs a better input impedance matching, we employ a broadband common-gate-common-source (CG-CS) LNTA and a current mirror to improve both gain and noise figure (NF) performance. Compared to the 50% duty-cycle switching stage, the 25% duty-cycle I-Q switching stage is implemented by using serial switches driven by 50% quadrature local oscillator (LO) signals separately, which improves the down-conversion gain by 3 dB and lowers the noise figure. The transimpedance amplifier employs the g(m)-boosting technique to realize low input impedance and high transimpedance gain. The core circuit (RF and baseband signal path) consumes 26 mW, and the prototype receiver achieves approximately 33-34.5-dB conversion gain, 8.1-9.35-dB NF and 7.5-9.8-dBm IIP3 from 0.8 GHz to 5 GHz.