A low-power SiGe-HBT merged LNA and mixer for 5 GHz wireless-LAN receivers

This paper presents the design, implementation and characterization of a monolithic image-rejecting merged low-noise amplifier and mixer. Without pre-amplification, the circuit fulfills the specifications for the RF front-end of a WLAN low-IF receiver compliant with the main 5 GHz standards. It consists of a noise and power matched transconductance, which feeds the current signal into two mixing differential pairs; two polyphase filters are used to generate LO quadrature signals and provide image rejection. Realized in a 120 GHz f_t commercial BiCMOS technology, the circuit exhibits up to 27 dB of voltage conversion gain, 32 dB of IRR, 7 dB of noise figure, -5 dBm and -14 dBm of iIP₃ and P_1dB respectively. Power consumption is 7.2 mW. The circuit targets low-power applications with a very high conversion-gain to power-consumption ratio: to the knowledge of the authors this is the highest reported for receiver front-ends in the 5-6 GHz band.