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

Abstract

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.