A 2.4GHz low-IF RF frontend for wireless sensor networks

This paper presents a low-power low-IF RF frontend for 2.4GHz wireless sensor networks (WSN) in 0.18μm RF CMOS technology. The RF frontend consists of a variable gain low noise amplifier (VG-LNA), a quadrature passive mixer and a divide-by-two circuit which generates the differential quadrature LO signals for quadrature balanced mixer. The effect of the input parasitic capacitance on the inductively degenerated common source LNA´s input impedance is analyzed in detail. An external LC network was used to achieve input matching under low power consumption. The proposed VG-LNA has three gain modes: high gain, medium gain and low gain modes. The gain control function can accommodate a high input level and satisfy the need dynamic range of WSN. The passive mixer shows high linearity, low 1/f noise and near zero power consumption. The measurement results of the frontend achieve 15dB voltage conversion gain, 4dB noise figure at the high gain mode, -1.5dBm input third order intercept point at the low gain mode, while the DC power consumption is 10.4 mW under a 1.8V supply voltage.