Research And Design Of High Gain Differential N-Path Band-Pass Filter

With the rapid development of the field of wireless communication,there are more and more frequency bands of communication protocols,so there is a need for filters that can operate in multiple frequency bands.Compared with traditional filters,the center frequency of N-path filters can be adjusted within a certain range,which has the advantages of high linearity,small size and easy integration,so N-path filters have received extensive attention from researchers and become an important choice for RF front-end filters.Traditional N-path filters typically use low-noise amplifiers to increase the amplification of the pass-band signal,but at the expense of the linearity of the circuit.In addition,although the N-path filter has achieved some results in the suppression of the 3rd and 5th harmonics,the suppression effect achieved by using the differential structure is limited for even harmonics.In addition,in the field of multi-mode and multi-frequency wireless communication,the bandwidth of the communication protocol is more numerous and dense,and the frequency selection characteristics of the N-path filter are poor.In order to solve the above problems,two high-gain N-path band-pass filters are designed,namely high-gain differential active N-path band-pass filter and high-gain differential passive N-path band-pass filter,and the specific work content is as follows:(1)A high-gain differential active N-path band-pass filter is designed,the band-pass filter and the band-reject filter are combined to reduce the bandwidth of the filter,and the band-pass filter adopts implicit capacitance superposition technology to improve the gain of the filter.The output of the filter adopts a network of transconductance amplifier and switched capacitors in parallel,which greatly suppresses the second harmonic of the filter.Based on TSMC 40 nm CMOS process to complete the circuit design,the circuit simulation results show that under the supply voltage of 1.1V,the center frequency of the filter can be adjusted in the range of0.2GHz～0.8GHz,when the center frequency is 500 MHz,IIP3 is greater than 11 dBm,the second harmonic suppression is 50 dB,the gain of the filter can reach 28.1dB,the gain of the filter is greater than 25 dB and the bandwidth is less than 10.5MHz in the entire frequency adjustable range.(2)A high-gain differential N-path band-pass filter is designed,and the high-gain implicit capacitor superposition technique is used to achieve 3x signal amplification in the single-stage circuit of the filter under the passive structure.In addition,the filter adopts a high-linearity capacitor switching circuit,which improves the linearity of the filter.Based on TSMC 40 nm CMOS process to complete the circuit design,the circuit simulation results show that under the supply voltage of 1.1V,the center frequency of the filter can be adjusted in the range of1.6GHz～2.4GHz,when the center frequency is 2GHz,IIP3 is greater than 22.8dBm,the gain of the filter can reach 26 dB,the gain of the filter is greater than 24 dB in the whole frequency adjustable range,and the noise figure is less than 4.6dB.