Research And Design Of Bandpass-to-Bandstop Reconfigurable N-Path Filter

With the rapid development of wireless communication technology,wireless communication devices need to cover multiple communication standards.The traditional receiver needs to use multiple of off-chip filters,which increases the volume and cost of the equipment,and is difficult to adapt to the development direction of full integration.N-path filters are widely used in RF receiver front-end due to their advantages such as adjustable center frequency,easy integration and small footprint.However,in complex interference environments,a single type of N-path filter has a poor filtering effect.At the same time,due to the influence of switch on-resistance and switch sampling characteristics,the filter also has out-of-band noise and harmonic noise problems,which limit the design of high-performance N-path filters.The main work and innovation of this paper are as follows:(1)Research and design a first-order bandpass-to-bandstop reconfigurable N-path filter.By controlling the on-off state of CMOS transmission gate,the switching of filter types is realized,and improve the adaptability of the filter.At the same time,the passive gain of bandpass filter is improved by using MOS capacitor parameter amplification technology,and the selectivity of bandstop filter is improved by using MOS capacitor sampling.Under the TSMC 40 nm CMOS process,the simulation results show that the tuning range of bandpass filter is 0.3GHz～1.4GHz,the gain is 6.1d B～9.1d B,and the Noise Figure is less than 3.3d B;The tuning range of the bandstop filter is from 0.3GHz～1.4GHz,the gain is-7.6d B～-11 d B,the bandwidth is 4.2MHz,and the Noise Figure is less than4.6d B.(2)In order to improve both harmonic rejection and out-of-band rejection,a second-order bandpass-to-bandstop reconfigurable N-path filter is designed.Miller feedback technology is used to improve the degree of freedom of out-of-band rejection of the filter.At the same time,the polyphase clock technology is used to eliminate the even and third harmonics of the filter.Under the TSMC 40 nm CMOS process,the simulation results show that the tuning range is 0.4GHz～2.6GHz,and the Noise Figure is less than5 d B;When the center frequency fs is 1GHz,the out-of-band rejection of the bandpass filter is 47 d B,and the even and third harmonic rejection is greater than 50 d B;The out-of-band rejection of the bandstop filter is 20 d B,and the even harmonic and third harmonic rejection is greater than 18 d B.The two filters designed in this paper can adapt to the complex communication environment.The first filter achieves passive gain enhancement and high reliability.The second filter has good harmonic suppression and out-of-band suppression.The theoretical analysis and simulation results of the two filters are basically consistent,with good comprehensive performance,and have broad application prospects in the RF receiver front-end.