Active and Passive Combined Mixer for Low Flicker Noise and Low dc Offset

A direct-conversion mixer with low flicker noise and low dc offset is presented for WLAN applications. The design consists of a folded-type active mixer with a resonant inductor in cascade with a source-driven passive mixer, operating at half the conventional LO frequency. Because of this unique topology, neither direct nor indirect flicker noise of the active mixer appears at the mixer output. Moreover, the dc offset voltage from the LO self-mixing is lowered, and the burden of designing a high-frequency VCO is relieved. The measurement results show a noise figure of 12.2 dB at 10 kHz, a conversion gain of 11.4 dB, and an IIP3 of -10.5 dBm while the mixer consumes 8.7 mW for a 1 V supply voltage. The design is implemented in a Dongbu Hitek 0.11 μm CMOS process with a chip area of 1.3 × 0.98 mm².