【正文】 en years, crystal filter below to some research: to achieve the best design, besides having the fine choose outside, still have good time domain response。 The color television receivers of tuning system surface b form filter. In addition, in the defense satellite munication systems has been widely adopted. Surface acoustic filter is electronics and acoustics product of integration of, and can be integrated, so, it all passive filter in the most promising. Various new filter too is various, somewhere, no longer described them. Our country at present the application of various filter proportion Our country39。 Ceramic filter harmonic surface each accounted for 1%。 Crystal filter accounted for 20%。 Extended working frequency。 Generalization of frequency domain filter and related product operation。 Function is small, can do less than 10 mW. The application of the SCF to audio range application as the main body, the work in 100 kHz frequency within. In signal processing applications are: SPC SCF, analog signal processing, vibration analysis, adaptive filter, music, resonance spectrum, prehensive language integrated device, tone selection, sounds coding, audio analysis, equalizer, modem, phase locked circuit, discrete Fourier transform...... In short, SCF, medical instruments in the meter measuring and data or information processing, and many other areas have broad application prospect. In our country, some 1978 graduate students began to mentor and conducted the research work, and really cause people to pay attention to is 1980 years later. Tsinghua university has made 1983 single chip SCF, chengdu academy of engineering and joint factory, developed a single piece of SCF. Now the key is to use MOS process realize SCF and application of a problem, because users don39。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 ratio of capacitance, has nothing to do with capacitance absolute value, so just cause the attention of people. In 1979, some developed countries monolithic SCF has bee a modity (are highly confidential technology). Now SC technology mature. The process to realize the MOS SCF, is recognized as the 80 s work theory and integrated process of a major breakthrough. The current MOS capacitance for a general method to 100 within pF skin, it has a (10 ~ 100) x 106 / V voltage coefficient and (10 ~ 100) x 106 / ℃ temperature coefficient, the two coefficient is close to ideal realm almost. SCF has the following some advantages: SCF can be large scale integrated。 Application linear transform method to explore the least an active element of filters need to continue to explore。t keep up, causing many new filter development in China and international development application for a short distance. 2, The classification of the filter There are different kinds of filter classification, generally has the following several kinds. (1) According to deal with signal type classification According to the processing signal type classification, may be classified as analog filter and discrete filter two kinds big. One simulation and can be divided into active filter, passive, three different classification。 隨著電子工業(yè)的發(fā)展，對濾波器的性能要求越來越高，功能也越來越多，并且要求它們向集成方向發(fā)展。 我國目前各種濾波器的應(yīng)用比例 我國現(xiàn)有濾波器的種類和所覆蓋的頻率已基本上滿足現(xiàn)有各種電信設(shè)備。通常應(yīng)用于：電視廣播發(fā)射機(jī)中作為殘留邊帶濾波器；在彩色電視接收機(jī)中調(diào)諧系統(tǒng)的表面梳形濾波器。近十年來，晶體濾波器致力于下面一些研究：實(shí)現(xiàn)最佳設(shè)計(jì)，除具有優(yōu)良的選擇外，還具有良好的時(shí)域響應(yīng)；尋求新型材料；擴(kuò)展工作頻率；改造工藝，使其向集成化發(fā)展。當(dāng)然，更多的應(yīng)用有待進(jìn)一步開拓。總之， DF 在數(shù)字信號處理技術(shù)中占有極為重要的地位，對于它的研究、生產(chǎn)和應(yīng)用等工作均是很有意義的。對于模糊和隨機(jī)噪聲干擾的二維圖像的處理，多維 DF 也能發(fā)揮很好的作用。 自 適應(yīng) DF 有如下一些簡單算法： W— LMS 算法、 M— LMS 算法、 TDO 算法、差值 LMS算法和 C— LMS 算法。此外，在靈敏度分析、噪聲分析等方面均有許多課題有待研究。 (2) 非的 MOS 開關(guān)的溝道電阻以及非理想的運(yùn)放特性，均可使 SCF 造成誤差。 1983 年清華大學(xué)已制成單片 SCF，成都工程學(xué)院與工廠聯(lián)合，也研制成單片 SCF。 SCF 具有下列一些優(yōu)點(diǎn)： SCF 可以大規(guī)模集成； SCF 精度高，因?yàn)槠湫阅苋Q于電容之比，而 MOS 電容之比的誤差小于千分之一；功能多，幾乎所有電子部件和功能均可以由 SC 技術(shù)來實(shí)現(xiàn)；比數(shù)字濾波器簡單，因?yàn)椴恍枰?A/D、 D/A 轉(zhuǎn)換；功能小，可以做到小于 10mW。 1979 年一些發(fā)達(dá)國家單片 SCF 已成為商品（屬于高度保密技術(shù)）。 四、開關(guān)電容濾波器（ SCF） 20 世紀(jì) 80 年代技術(shù)改造一個(gè)重大課題是實(shí)現(xiàn)各種電子系統(tǒng)全面大規(guī)模集成（ LSI）。但由于采用預(yù)置電路和復(fù)雜的相位時(shí)鐘，使這種濾波器發(fā)展前途不大。由于R 的存在，給集 成工藝造成困難，于是又出現(xiàn)了有源 C 濾波器：就是濾波器由 C 和運(yùn)放組成。 1965 年單片集成運(yùn)算放大器問世后，為有源濾波器開辟了廣闊的前景。 （ 2）按選擇物理量分類 按選擇物理量分類，濾波器可分為頻率選擇、幅度選擇、時(shí)間選擇（例如 PCM 制中的話路信號）和信息選擇（例如匹配濾波器）等四類濾波器。 （ 1）按處理信號類型分類 按處理