Design Of Widely Tunable And Configurable Complex Filter

The progress of integrated circuit manufacturing technology and the improvement of wireless communication have prompted the development of radio frequency chips to the trend of high integration, low power consumption and low cost. Complex filter is an important module in low-IF receiver, which realizes the image rejection and channel selection functions. At the same time, flexible frequency tuning capability of the filter can make the receiver meet the requirements of different communication standards. As a conclusion, it has an important research value to design a widely tunable and configurable complex filter.The main objective of this thesis is to design a widely tunable and configurable complex filter used in Low-IF receiver. The basic concepts of filters are introduced, including key parameters of Gm-C filters and two different ways of designing Gm-C complex filters. According to the requirements of wireless receiver, the parameters and specific design programs of Gm-C filter are determined. Firstly, we use cross-coupling transconductors to translate the frequency response of fourth-order Gm-C low-pass filter to complex band-pass response. Then, we design a widely tunable transconductor based on current conveyor, which achieves a precise ratio of transconductance (Gm) in the filter. To meet the requirement of frequency tuning and calibration, a novel master-slave Gm control circuit is designed to control the transconductance in the filter, which translates Gm to a variable that is exactly proportional to the capacitance C, thus eliminating effects of process deviation on time constant C/Gm. Therefore, the frequency tuning and calibration of Gm-C filter can be realized simultaneously.The schematic and layout designs of the widely tunable and configurable Gm-C complex filter are completed based on SMIC 0.18μm CMOS process, and also taped out for verification. According to the different bandwidth of Gm-C filter, the static current is 1.6mA～2.1mA at 1.8V power supply. The measurement results show that the filter has a tunability of center frequency from 147kHz to 1.95MHz and bandwith from 94kHz to 1.96MHz independently. The complex filter gives above 20dB image rejection. Meanwhile, the filter achieves an in-band 3rd order harmonic input intercept point (IIP3) above 12.8dBm. Thus the measurement results meet the design aims.