The Research And Design Of N-path Filter

With the wide application of IC products to all aspects of civilian and military fields,people also constantly improve the requirement for the performance of the integrated circuit.As one of the most widely used units of communication system,the filter plays an important role in the acquisition,transmission and processing of signals.In most cases,the performance of the filter will have a decisive impact on the performance of the whole system.Therefore,with the development of information science and technology,especially the wireless communication technology,the requirement of the function and performance of the filter is improved.Due to the features of direct tunability with clock frequency,potentially higher quality factor compared to on-chip CMOS LC filters,high linearity and graceful scaling with process,N-path filters attract a lot of people’s interest.The purpose of the article is not only to give an in-depth study for N-path filtering technique,but also to design the N-path filter circuit with excellent performance.In order to achieve this purpose,the first work is to detailed research and analysis of integrated circuit theory that N-path filters designer needs to know,besides,make an intensive study of the Miller filtering technique,the center frequency shifting technique and the gain-boosted technique.Then,based on the theoretical research,the paper had completed the design and simulation of the following three kinds of N-path filters:(1)A single-end Miller N-path bandpass filter is designed by using the Miller filtering technique is carried out.It realizes the capacitance multiplication,can effectively reduce the chip area,and realizes the on-resistance of the switches,thereby reducing the power consumption of the local oscillator.Through the pre-simulation of the 8-path bandpass filter,it shows that the filter is tunable from 0.2 GHz to 2.3 GHz with approximately constant bandwidth of 5 MHz.It exhibits 17-18.9dB gain,5.4 dB NF,and 8.7-dBm IIP3 at 150-MHz offset.(2)A fully differential Miller N-path bandpass filter is designed,which is based on the subtraction of two N-path filters with slightly different center frequencies to increase the filter bandwith and order.At the same time,using the center frequency shifting technique,the two N-path networks with different center frequencies are generated by a clock control,and the center frequency of each N-path filter is same shifted relative to its clock frequency(one upward and the other one downward).Through the pre-simulation of the 8-path bandpass filter,it shows that the filter is tunable from 0.2 GHz to 2.3 GHz with a bandwidth of 40 MHz.It exhibits 26～27.8dB gain,8.2 dB NF,and 21.5-dBm IIP3 at 150-MHz offset.(3)A N-path filter with two purposes of notch filtering and bandpass filtering is designed by using the gain-boosted technique and clock difference technique.The circuit has the characteristics of simple structure and easy realization of two kinds of filtering.The 8-path filter has taken out the pre-simulation,layout design and post-simulation.The results of the filter’s post-simulation show that the filter is tunable from 0.2 GHz to 2.2 GHz.It exhibits 8.0～9.2dB gain with bandpass filtering,and-5～-4dB gain with notch filtering,while the ultimate rejection of the filter is 22dB.The IIP3 of the filter is 13.3-dBm at 150-MHz offset and the NF is 4.2 dB.