Research And Design Of Miller N-path Filter With High Out-of-band Rejection

In recent years,with the rapid development of integrated circuit technology and wireless communication technology,N-path filters have once again attracted widespread attention.In order to meet the increasing demands of receiver complexity and flexibility,a fully integrated,highly adjustable front-end RF filter is required.The potential candidate of the front-end RF filter is the N-path filter,which is widely used in the communication field and radio receiver system due to its advantages such as highly adjustable center frequency,small size,and easy integration.However,the design of the N-path filter still has great challenges.For example,the out-of-band rejection is limited by the switch resistance,and there are problems such as harmonic noise at a multiple of the switching sampling frequency.These problems seriously affect the performance of the N-path filter.This article aims to conduct an in-depth study on the out-of-band rejection and harmonic rejection mechanisms of N-path filters.The N-path filtering technology is analyzed in detail,the basic concepts and main performance indicators of the N-path filter are introduced,and the following are designed for the current passive N-path filter without gain,low out-of-band rejection,harmonic noise,etc.Two Miller N-path filters with high out-of-band rejection were simulated and verified using Cadence software.The main work and innovations of this paper are as follows:(1)Research and design a Miller N-path band-pass filter with single-ended input and single-ended output.By cascading a capacitive coupling N-path network at the input end of the active filter,and cascading an inductive coupling N-path network at the output end,a transmission zero is introduced on both sides of the pass-band to improve the out-of-band rejection capability on both sides of the pass-band.Under the TSMC 40nm CMOS process,the filter is simulated and verified.The results show that the center frequency of the filter is adjustable from 0.6GHz to 1.2GHz under the 1.1V power supply voltage,and the gain is higher than 5d B within the tuning range.When the center frequency f_s=1GHz,the maximum out-of-band rejection reaches 48d B.The designed filter has both high gain and high out-of-band rejection characteristics.(2)Research and design a Miller N-path band-pass filter with double-end input and double-end output.By cascading a dual-switch N-path filter network with a phase difference of180°at the output of the active N-path filter,the limitation of the switch resistance is eliminated,thereby improving out-of-band rejection.Using three-path differential technology to suppress even and third harmonics.The design adopts TSMC 40nm CMOS process.Cadence simulation results show that under 1.1V supply voltage,the center frequency tuning range is 0.3?1.3GHz.Within the above tuning range,the gain is higher than 15d B and the noise figure is less than 2d B.When the center frequency is at 1GHz,the second,third,and fourth harmonic rejection are 25d B,30d B,and 35d B,respectively,and the maximum out-of-band rejection reaches 43d B.Both Miller N-path filters have the characteristics of high rejection,high gain,and low noise,and the results of the pre-simulation and post-simulation are in good agreement with the theoretical analysis,and the overall performance is high,which is suitable for high-performance wireless receivers.