Design Of High Order Linear Phase Switched Capacitor Filter

Switched-capacitor filter began to emerge in our country from the1970s. Thinkabout all kinds of filters, the switched-capacitor filter occupies important positionbecause of its absolute advantage in recent years. Then it has been widely used inpractical engineering design. This article is based on the project of high order low-pass filter in velocity-variation parameter transducer of MEMS center, to design aswitched capacitor of linear phase filter. This kind of filter have group delay almostacross the transmission bands, thus it can keep the filtered signal waveform best inthe transmission bands.After choose the best one called Bessel filter that can get the linear phase, thisarticle uses MATLAB to simulate and make sure the number of order and thetransfer function. Then calculate the pole position. To achieve better linear phase,this article uses a ten-ordered filter model to design. During the circuit designing, itdivides the high-order filter to several second-order filters, and designs themrespectively. For the design of second-order filter, it uses a classic structure of asecond ordered switched capacitor circuit.In the designing of the switched-capacitor filter, the switch and clock are veryimportant. This article presents a six CMOS unit to be a switch, it can reduce thechannel charge effect and the clock feed through effect. Then uses a two-phase non-overlapping clock make up by convert and NAND circuit. When calculate the valueof capacitor, it uses the method of normalization, and can change the cutofffrequency by change the capacitor. During the designing of op amp in the switched-capacitor circuit, this article uses the classic folded cascode structure, and adds incapacitor compensation.This article uses the Cadence to simulate the circuits that were designed, and usesa frequency-domain simulation method called PSS and PAC simulation. The resultsshow that the designed circuits work normally, the band roughness reaches0.00067dB, the2times cutoff frequency attenuation reaches45.6dB, total harmonicdistortion reaches-62.5dB, and the phase is basically linear, all of the work meetsthe requirements.