【文章內(nèi)容簡介】 choose physical quantities classification According to choose physical quantities classification, filter can be divided into frequency selection, amplitude selection, time to choose (such as the words of PCM signals) and information choice (for example matching filter), and other four kinds of filter. (3) By frequency bandpass range classification According to the classification with frequency range, filter can be divided into low pass, qualm, bandpass, take resistance, all the five categories, and b form bandpass filter belong to stop filter and belt, because it has periodic bandpass and stopband. Filter sort is various, some are well known, some may not be what we are familiar with, introduced in recent years the development of several filter soon. 3, Active filter By the following active power filter some active ponents: operational amplifier, the negative resistance, capacitance and inductance, negative negative frequency rheostat (FDNR), generalized impedance transformer (GIC), negative impedance transformer (NIC), are impedance transformer (PIC), negative impedance inversion device (NII), are impedance inversion device (PII), four kinds of controlled source, in addition, there is a very sick son and son zero ponents. 1965 monolithic integrated operational amplifier advent, for active filter opened up broad prospects. In the early 70 s, active filter development conspicuous, 1978 single chip RC active filter e out, for filter integrated into wele step. Due to the opamp the ripples of gain and phaseshift are of the frequency of function, this limits the range of frequencies RC filter, general working frequency for about 20 kHz, after pensation, working frequency also limited to 100 kHz less than. 1974 years produced more high frequency RC active filter, and cause the work to frequency of GB / 4 (GB for opamp gain and bandwidth of the product). Due to the existence of R, integrated process to cause difficulties, and he appeared active C filter: is by C and opamp filter position. Such easy to integration, more important is to improve the precision of the filter, because the performance of the filter active C depends only on the ratio of capacitance, has nothing to do with capacitance absolute value. But it is a major problem: because each branch ponents are capacitance, so opamp no dc feedback channel, that stability is a difficult problem. 1982 by Geiger, Allen and Ngo with continuous switch proposed resistance (SR) to replace active RC filter the electrical resistance R, constitutes the SRC filter, it still belongs to the simulation filter. But due to the preset circuit and plex of the phase of the clock, the filter development prospect is not big. In short, by the RC active filter is a prototype of all kinds of variant active filter to remove inductors, small volume, Q value can reach 1000, overe the RLC passive filter is big, Q value of small faults. But it still has many topic needs further research: ideal opamp and practical characteristics of the deviation。 Due to the active filter hybrid integrated process improvement, monolithic integrated needs further research。 Application linear transform method to explore the least an active element of filters need to continue to explore。 Components of the absolute value of tolerance, the existence of precision and performance influence filter the problem is still not solved。 Because R exist, integration of chip the area is large, resistance error (20% ~ 30%), poor linearity disadvantages, making large scale integrated still having difficulty. Although there are so many questions, RC active filter theory and application is still in sustainable development. 4, Switch capacitance filter (SCF) The 1980 s technology reform a major issue is the realization of various electronic system in large scale integration (LSI). Use most filters bee tiger, RC active filter can39。t achieve LSI, passive filter and not to mention the mechanical filter, and so, people can only additional monarch new size. 50 s there has been put forward the concept of SCF, because at that time integration process doesn39。t pass, and did not cause the attention of people. In 1972, the United States a call Fried scientists published with a switch and capacitance simulation resistance R, said the performance of the SCF depends only on the rati