數(shù)字濾波器結(jié)構(gòu)ppt課件

1、數(shù)字濾波器構(gòu)造數(shù)字濾波器構(gòu)造DFDigital Filter)一、什么是數(shù)字濾波器一、什么是數(shù)字濾波器 顧名思義：其作用是對(duì)輸入信號(hào)起到濾波的作用；即DF是由差分方程描畫的一類特殊的離散時(shí)間系統(tǒng)。 它的功能：把輸入序列經(jīng)過一定的運(yùn)算變換成輸出序列。不同的運(yùn)算處置方法決議了濾波器的實(shí)現(xiàn)構(gòu)造的不同。數(shù)字濾波器引見 Digital filters are used for two general purposes: (1) separation of signals that have been combined, (2) restoration of signals that have been

2、distorted in some way.研討DF實(shí)現(xiàn)構(gòu)造意義1.濾波器的根本特性如有限長(zhǎng)沖激呼應(yīng)FIR與無限長(zhǎng)沖激呼應(yīng)IIR決議了構(gòu)造上有不同的特點(diǎn)。2.不同構(gòu)造所需的存儲(chǔ)單元及乘法次數(shù)不同，前者影響復(fù)雜性，后者影響運(yùn)算速度。3.有限精度有限字長(zhǎng)實(shí)現(xiàn)情況下，不同運(yùn)算構(gòu)造的誤差及穩(wěn)定性不同。4.好的濾波器構(gòu)造應(yīng)該易于控制濾波器性能，適宜于模塊化實(shí)現(xiàn)，便于時(shí)分復(fù)用。二、數(shù)字濾波器的任務(wù)原理則：是其付氏變換。是系統(tǒng)的輸出，是其付氏變換。是系統(tǒng)的輸入，設(shè))()()()(jwjweYnyeXnxh(n)x(n)y(n)作原理。這就是數(shù)字濾波器的工符合我們的要求，使濾波器輸出選取表示）后變成其系統(tǒng)性能

3、用經(jīng)過濾波器看出：輸入序列的頻譜)()(),()()()()()()()()()(1jwjwjwjwjwjwjwjwjwmeHeXeHeHeXeHeXeHeXFmxmnhny那么LTI系統(tǒng)的輸出為：三、數(shù)字濾波器表示方法 有兩 種表示方法：方框圖表示法；流圖表示法. 數(shù)字濾波器中,信號(hào)只需延時(shí)，乘以常數(shù)和相加三種運(yùn)算。 所以DF構(gòu)造中有三個(gè)根本運(yùn)算單元：加法器，單位延時(shí)，乘常數(shù)的乘法器。1、方框圖、流圖表示法、方框圖、流圖表示法Z-1單位延時(shí)系數(shù)乘相加Z-1a方框圖表示法：方框圖表示法：信號(hào)流圖表示法：信號(hào)流圖表示法：a把上述三個(gè)根本單元互聯(lián)，可構(gòu)成不同數(shù)字網(wǎng)絡(luò)或運(yùn)算構(gòu)造，也有方框圖表示法和流

4、圖表示法。2.例子)() 2() 1()(021nxbnyanyany例：二階數(shù)字濾波器：其方框圖及流圖構(gòu)造如下：Z-1Z-1x(n)y(n)b0a1a2x(n)y(n)b0a1a2Z-1Z-1看出：可經(jīng)過流圖或方框圖看出系統(tǒng)的運(yùn)算步驟和運(yùn)算構(gòu)造。以后我們用流圖來分析數(shù)字濾波器構(gòu)造。DF網(wǎng)絡(luò)構(gòu)造或DF運(yùn)算構(gòu)造二個(gè)術(shù)語有微小的差別，但大抵一樣，可以混用。四、數(shù)字濾波器的分類 濾波器的種類很多，分類方法也不同。 1.從功能上分；低、帶、高、帶阻。 2.從實(shí)現(xiàn)方法上分:FIR、IIR 3.從設(shè)計(jì)方法上來分：Chebyshev(切比雪夫,Butterworth巴特沃斯 4.從處置信號(hào)分：經(jīng)典濾波器、現(xiàn)

5、代濾波器 等等。1、經(jīng)典濾波器 假定輸入信號(hào)x(n)中的有用成分和希望去除的成分，各自占有不同的頻帶。當(dāng)x(n)經(jīng)過一個(gè)線性系統(tǒng)即濾波器后即可將欲去除的成分有效地去除。但假設(shè)信號(hào)和噪聲的頻譜相互重疊，那么經(jīng)典濾波器將無能為力。 |X(ejw)|wwc有用無用wc|H(ejw)|Y(ejw)|wwc2.現(xiàn)代濾波器 它主要研討內(nèi)容是從含有噪聲的數(shù)據(jù)記錄又稱時(shí)間序列中估計(jì)出信號(hào)的某些特征或信號(hào)本身。一旦信號(hào)被估計(jì)出，那么估計(jì)出的信號(hào)將比原信號(hào)會(huì)有高的信噪比。 現(xiàn)代濾波器把信號(hào)和噪聲都視為隨機(jī)信號(hào)，利用它們的統(tǒng)計(jì)特征如自相關(guān)函數(shù)、功率譜等導(dǎo)出一套最正確估值算法，然后用硬件或軟件予以實(shí)現(xiàn)。 現(xiàn)代濾波器實(shí)

6、際源于維納在40年代及其以后的任務(wù)，這一類濾波器的代表為：維納濾波器，此外，還有卡爾曼濾波器、線性預(yù)測(cè)器、自順應(yīng)濾波器。本課程主要講經(jīng)典濾波器，外帶一點(diǎn)卡爾曼濾波器.3.模擬濾波器和數(shù)字濾波器 經(jīng)典濾波器從功能上分又可分為： 低通濾波器LPAF/LPDF):Low pass analog filter 帶通濾波器(BPAF/BPDF):Bandpass analog filter 高通濾波器(HPAF/HPDF):High pass analog filter 帶阻濾波器(BSAF/BSDF):Bandstop analog filter 即它們每一種又可分為：數(shù)字(Digital)和模擬(A

7、nalog)濾波器。4.模擬濾波器的理想幅頻特性cc)( jHcc)( jHcc)( jH)( jH1c2c1c2cLPAFHPAFBPAFBSAF5.數(shù)字濾波器的理想幅頻特性2c)(jweHLPDFHPDFBPDFBSDF.23.2.2)(jweH)(jweH)(jweHAnalog filters and digital filters Analog filters are cheap, fast, and have a large dynamic range in both amplitude and frequency. Digital filters, in comparison,

8、are vastly superior in the level of performance that can be achieved. With analog filters, the emphasis is on handling limitations of the electronics, such as the accuracy and stability of the resistors and capacitors. digital filters are so good that the performance of the filter is frequently igno

9、red. The emphasis shifts to the limitations of the signals, and the theoretical issues regarding their processing linear filter has an impulse response, a stepresponse and a frequency response. Each of these responses contains complete information about the filter, but in a different form. The most

10、straightforward way to implement a digital filter is by convolving the input signal with the digital filters impulse response. another way to make digital filters, called recursion. Recursive filters: using previously calculated values from the output, besides points from the input. Instead of using

11、 a filter kernel, recursive filters are defined by a set of recursion coefficients. recursive filters are also called Infinite Impulse Response or IIR filters. In comparison, filters carried out by convolution are called Finite Impulse Response or FIR filters.Time Domain Parameters Three parameters

12、are important: (1) transition speed (risetime), shown in (a) and (b) (2) overshoot, shown in (c) and (d), (3) phase linearity (symmetry between the top and bottom halves of the step), shown in (e) and (f).Frequency domain filterscutoff frequency The division between the passband and transition band

13、is called the cutoff frequency. In analog filter design,the cutoff frequency is usually defined to be where the amplitude is reducedto 0.707 (i.e., -3dB). Digital filters are less standardized, and it is common to see 99%, 90%, 70.7%, and 50% amplitude levels defined to be the cutoff frequency.Frequ

14、ency Domain Parameters roll-off ripple stopband attenuation A fast roll-off meansthat the transition band is very narrow.Passband frequencies to move through the filter unaltered, there must be no passband ripple, stopband attenuationMoving Average Filters The moving average is the most common filter in DSP, mainly because it is the easiest digital filter to understand and use. In spite of its simplicity, the moving average filter is optimal for a common task: reducing random noise while retaining a sharp step response. the moving average is the worst filter for frequency domai