Research And Implementation Of Programmable Switch Capacitor Filter System

In this dissertation, a system of programmable filter based on switch capacitor filter MAX260 by using FPGA as the main controller is designed. The programmable filter possesses many functions. It can provide both Butterworth and Chebyshev filters up to 8 orders, and realizes automatic tracking filtering at the fundamental frequency of signal. It's easy and flexible to change the parameters of the filter. The filter is agility to control and user friendly, and has a certain application value.The main achievements obtained by this dissertation are:Firstly, based on a lot of studies in programmable design of switch capacitor filter, a complete set of methods of switch capacitor filter design based on MAX260 was proposed. The computational formulas of filter parameters including low-pass, high-pass and band-pass through analyzing elementary second-order filter were obtained. The method of converting each filter parameters into programmable parameters of switch capacitor filter was elaborated systematically. Meanwhile, this thesis introduced the design procedures of programmable filter system, and calculated a large amount of design parameters of filter. Although this method was presented based on switch capacitor filter MAX260, it has a certain reference value to universal switch capacitor filter design.Secondly, the hardware design of the programmable filter system based on switch capacitor filter has been finished. The hardware design of amplification and detection circuit, gain controlling circuit, filter module circuit, FPGA controlling circuit and interface circuit of the filter system were expounded detailedly in the paper. A method improving the dynamic range with programmable amplifier consisting of dual D/A converters was proposed.Thirdly,the method of controlling programmable filter system by FPGA was elaborated in detail,and the software design of each circuit was expatiated concretely. Through studying and analyzing the method which generate clock signal of switch capacitor filter with FPGA, a universal design method that generate clock signal of switch capacitor filter was obtained. The method generates clock signal with different frequency via the divider and frequency divider. It calculated the storage list of divisors and dividends through divider design formulas according to different system work mode,and realized complicated multi-bit division operation through relatively simple shifting-subtracting algorithm.Finally, aiming at the problem that switch capacitor filter existing aliasing phenomenon, a method constructing anti-aliasing filters separately for different frequency bands was proposed. A low-pass filter with fixed cut-off frequency is adopted for anti-aliasing in high-frequency band; the anti-aliasing capacity of programmable filter system in low- frequency band is improved effectively by using low-pass switch capacitor filter which adjusts its cut-off frequency in real time.