Design Of Eighth-order Low-pass Elliptical Switched Capacitor Filter

The localized substitution of analog integrated circuits is currently a hot spot in the industry.Chips used in the military and aerospace fields have a significant impact on our country's development,and the importance of localized substitution is even more prominent.Fast-changing parameter sensors are widely used in the aerospace field.The goal of this subject is to provide a highly integrated high-order low-pass filter chip for fast-changing parameter sensors.Compared with other traditional filter structures,the switched capacitor filter has the advantages of high accuracy and good integration,and is suitable for low-frequency and high-precision measurement systems.This subject is based on the principle of switched capacitor filters,and carried out the design and research of eight-order switched capacitor filters with adjustable cut-off frequency.In this subject,a low-ripple,low-transition ratio,high-stop-band attenuation switched capacitor low-pass filter is designed,which realizes the adjustable cut-off frequency and is insensitive to capacitor mismatch.This paper studies the principle of the switched capacitor sub-module in detail,and analyzes the electrical principle of the switched capacitor filter from the perspective of time domain and z domain.After applying the superposition principle to split the complex switched capacitor network structure and the signal flow diagram technology to simplify the analysis process,the basic mathematical model of the switched capacitor filter is established,and various filter approximation functions are studied according to the index requirements.The elliptic filter function structure required by the design of the slope of the large transition band,the transfer function is calculated in detail,and the stability of the system is verified.Aiming at the system structure,the ladder method is used to complete the high-order switched capacitor filter design.The whole process from the passive ladder circuit equivalent to the switched capacitor is analyzed in detail,and the difference between the capacitor mismatch and the cascade method and the ladder method is analyzed.influence level.In order to improve the dynamic range of each level of the filter,dynamic scaling and parameter optimization of scale calculations are carried out,the design of the switched capacitor filter circuit level is completed,and all the modules required to build a switched capacitor circuit are designed,including differential amplifiers and six tubes.Transmission gate switch,two-phase non-overlapping clock generator and bias module,and build the overall circuit simulation verification of the filter.Completed all the technical index requirements of the subject.This subject uses 0.35?m BCD technology for layout design,and completes DRC,LVS inspection and post-simulation verification.The cut-off frequency is adjustable from 30 Hz to 10 k Hz,the passband ripple is less than 0.4d B,the transition ratio is 1.5,and the stopband attenuation is greater than 70 d B.The performance index of the switched capacitor low-pass filter is required.