Research And Design Of Active Low-pass Filters In CMOS

Active analog filter plays an important role in the field of communication and signal processing.With the increase of analog signal bandwidth,the design of high frequency filter becomes more and more important.Although the Amp-RC filter can obtain very high linearity,it is difficult to improve the bandwidth of the filter due to the limitation of the gain bandwidth product of the operational amplifier.In this paper,the design of continuous-time active low-pass filter with high frequency and low power consumption is studied.Then two kinds of low pass filter with Butterworth type were discussed and designed.In the design of Gm-C filter,the principle and application of transconductance amplifier are introduced,and the transconductance amplifier with wide swing,high linearity and low power consumption is given.Based on the complementary differential pairs the transconductance gain is improved significantly without increasing the power consumption.The six order Butterworth filter is designed by the cascade of three second-order cell.A very simple automatic tuning system corrects the filter deviations due to process parameter tolerances and temperature variations.And the tuning sensitivity can be improved by using the differential tuning method.In the design of source-follower filter,the advantages of source-follower is discussed.And then the source-follower-based second-order cell is designed with NMOS transistor.Finally a six-order cascaded Butterworth low-pass filter.In order to deal with the impact of process deviation,3-bit controlled capacitor array with the tuning range of ±25%is designed.The Gm-C filter and the source-follower filter are realized in a 65nm CMOS at a 1.8V supply.Both of them achieve a less then-50dB HD3 with 3dB bandwidth of 880MHz.The power consumption of them are 16 mW and 2 mW,respectively.