CMOS subharmonic downconverter using an LNTA front-end

To mitigate the higher noise figure (NF) of CMOS-based subharmonic mixers (SHMs) relative to their diode-based counterparts, this paper proposes the use of a low-noise transconductance amplifier (LNTA) ahead of the mixing core. The LNTA has a noise-cancelling topology that enables the mixer to have a high conversion gain and low NF over the RF input band of 4.5 GHz to 8.5 GHz. A chip was fabricated on a standard 130 nm CMOS process to validate the concept and measurement results reveal that the mixer can yield a conversion gain of 14.5±1.5 dB and a double-sideband noise figure of 9.25±1.25 dB over the RF band. The mixer´s IP_1dB is -10.8 dBm and its IIP₃ is -3.7 dBm while its IIP₃ is +6.5 dBm and its OIP₃ is +13.8 dBm. The circuit core occupies an area of 0.49 mm² on the silicon die.