Design Of Low Voltage Low Power Filters For WSN Nodes Application

Wireless Sensor Network (WSN) is a wireless communication network which is composed of a large number of cheap micro-sensor nodes; it can monitor physical or environmental conditions in different locations. The main problem of WSN application is how to improve its power efficiency. With the development in integrated circuit technology, the block which consumes the most power is RF transceiver chip. As an important module of the RF transceiver chip, reducing the power consumption of low-pass filter (LPF) and complex band-pass filter (CBPF) have great significance for the entire system.This thesis presents design and analysis of low power LPF and CBPF based on 0.18μm CMOS process, which are applied in RF transceiver of WSN. The LPF is fourth-order Butterworth Gm-C filter, cascade by tow-power second-order sections, and biased by current of positive temperature coefficient and the transconductance of filter remain constant while temperature is change, so the frequency characteristics of filter remain stable in the temperature range -50～80℃. The structure of CBPF is fourth-order Gm-C bandpass filter. The transconductor for frequency translation is fully differential structure, and deploy MOSFET that work in triode region as the source degradation resistance to broaden the linear range of transconductor. Also, an automatic frequency tuning circuit is used to compensate for the variations due to the temperature and process corners variation. The measured results of LPF chip shows, bandwidth is about 1.584MHz, channel rejection ratio is 37.71dB at 5MHz, and the current consumption is 50μA under 1V supply voltage. The measured results of CBPF with automatic frequency tuning circuits show, bandwidth is cover 0.8MHz-3.1MHz, the adjacent channel signal (7MHz) rejection ratio is more than 40dB, the image signal (-2MHz) rejection ratio is 32dB and the current consumption is 382μA under 1V supply voltage.In this thesis, the designs of CMOS LPF and CBPF under 1V supply are presents. The measured results show circuits works well to achieve low power requirements. LPF and CPBF can be applied to RF transceiver chip of WSN.