Fast Response Non-drift Active Low-pass Filter

Filtering technology is critical in the field of information processing. Filters have become an integral part of information processing, data communication, instrumentation, automation and control field. As a discipline, filtering has gone through nearly one hundred years, experienced from passive to active, from the discrete to the monolithic integration, from analog to digital and then to simulate the course of development. Within this time, it has smaller size, lower cost and greatly enhances the accuracy and reliability.In the scientific and production activities, a great deal of information is carried by the weak low-frequency signals. In the noisy environment, in order to achieve low frequency signal’s acquisition and processing, the research and design of the low-pass filter is particularly important. Compared with passive RC filter, the active low-pass filter using active amplifier, performs more excellent and is easier to monolithic integration. As active low-pass filter, in order to achieve a better filtering effect, we should consider not only noise suppression, but also how to minimize the introduction of the active device’s attached drift. In addition, filtering system’s response time directly determines the total delay of the system in some occasions, which real-time is a critical requirement. If additional drift of the channel is inhibited and at the same time, the response time of the filter is shortened, it has very important significance for innovative filter theory and anti-jamming design, as well as practical engineering design applications.This paper proposes a basic circuit with non-drift in channel. The basic circuit can constitute arbitrary order’s active low-pass filter without drift. Pspice has verified that there is no channel additional drift in the finite-order low-pass filter constituted by the basic circuit. On this basis, the article also studies how to improve the filter’s response speed and an effective solution is proposed. The main idea of the solution is that the channel’s voltage signal is fed back by an attenuation feedback network, through the main amplifier in the system based on the original circuit. At last, the signal is fed back to the filter’s active amplifier positive input. Thus, the charge and discharge time of capacitors in the filtering system is significantly reduced. Accordingly, the filter’s response time is greatly reduced, too. Pspice simulation results show that filter’s response time is significantly shorter.