Design Of Highly Linear And Frequency Tunable Gm-C Complex Filter

Complex filter is an important module in low-IF receiver, which realizes the image rejection and channel selection functions. Flexible frequency tuning capability of the filter adapts the receiver to different applications, and good linearity can reduce the error rate of the receiver. So research in highly linear and frequency tunable filter is important for the realization of the entire RF receiver system.The main objective of this thesis is to design a Gm-C complex filter for a Low-IF receiver used in wireless sensor network. Firstly, the basic principles of Gm-C filter and image rejection receiver is analyzed. The ways of designing complex filter are also introduced. Then parameters and the specific design programs are given according to the performance indicators of the receiver. Including:Uses multiple integrator loop feedback method to design the topology of a novel 4th order Gm-C complex filter, guaranteed minimum number of components and low sensitivity to the components’parameter; Designs a high linearity transconductor based on current conveyor, which achieves a precise ratio of transconductance (Gm) in the filter; To meet the requirement of frequency tuning, a master-slave Gm control circuit is designed to control the transconductance in the filter, which translates the time constant from C/Gm to RC; Based on this circuit, a lower power consumption automatic frequency calibration circuit is presented to resist the process errors, which is originally used for active-RC filter.The highly linear and frequency tunable Gm-C complex filter was taped out in SMIC 0.18-μm CMOS technology. The power consumption of the complex filter is 2mW with the 1.8V power supply. The measurement results show that the filter has a tunability of center frequency from 141kHz to 453kHz and bandwith from 92kHz to 837kHz independently. The complex filter gives above 20dB image rejection. Meanwhile, the filter achieves an in-band 3rd order harmonic input intercept point (IIP3) above 17dBm. Thus the measurement results meet the receiver system requirements.