The Research On None-drift Active Low-pass Filter With Time-Varying Parameters

Filtering is an important concept in modern signal processing. It is a key issue to design a filter with good performance. Filters are devices with frequency selectivity. That is, a filter allows signal component with frequency in the pass-band to pass by, and repress signal component with frequency in the stop-band. For a long time, massive fundamental information in science and production activity loading on low frequency weak signal, so, low pass filter is widely applied to get the information and be designed to anti-jamming under the noise environment. Introduction of the low-pass filter in the direct-current path is an effective method to suppress noise, especially frequency noise. But passive RC filter can only implement the special transfer function with apices in negative x-axis and single radix, the active RC low pass filter is most suitable low frequency filters system. However, introduction of the active RC filter can all import additive drifting which is produced by active devices. In domain of sea monitor, geological prospecting, construction, biomedicine, electrochemistry and so on, the system sensitivity in low frequency weak signal transmission, examination system and high accuracy instrument often reaches uV even nV. So at that time additive drifting has the same serious issue with noise.In the filter design, we hope the filters have good amplitude-frequency characteristic in the pass-band, namely short rise time in the output signal. In many fields of signal processing, the response speed is as important as the accuracy. However, the conventional typical filters can hardly satisfy both of the requirements at the same time. The goal of this article is in research of establishing the non-drifting active time-varying low pass filter system theory and the realization method, which aims to provide techniques and theory of reference for practical implementations.The main work and in this article are:(1) In analog domain non-drift all-pole active low-pass filters are introduced, including the circuit structure, the analysis of its theory and the simulation results. When compared to the conventional active low-pass filters, the low-pass filters have low-drift. (2) On the basis of the non-drift active low-pass filters, time-varying low-pass filters are introduced in this paper, which mean the parameters are changed with time. In the proposed filters, significant shortening of the transient state achieved.Simulations and practical applications show that the time-varying techniques proposed in the paper are effective and useful, and have great value in practical engineering implementation. The simulations in the article are all compiled and edited in Pspice and Multisim.