【正文】 阻帶幅頻響應規(guī)格給予一些可接受的公差。（ ）為低通濾波器。由于脈沖響應對應于所有這些都是非因果和無限長，這些過濾器是尚未實現(xiàn)的理想。 我們在這方面限制的幅度逼近問題的唯一一章我們的注意。如第 ，所設計的濾波器可以通過級聯(lián)與全通區(qū)段糾正相位響應。在某些情況下，單位采樣響應或階躍響應可能被指定。我們還討論了傳遞函數適當的調整。在一節(jié)中，我們首先檢查了這兩個問題。首要的問題是一個合理的濾波器的頻率響應規(guī)格從整個系統(tǒng)中數字濾波器將被雇用的要求發(fā)展。為此，我們限制我們討論了 MATLAB在確定傳遞函數的使用。然后，我們考慮到另一種類型，它是由一個函數代替復雜的變量 z達到了一個 IIR濾波器的傳遞函數 z的類型轉換四種常 用的轉換進行了總結。一種廣泛使用的方法來設計IIR濾波器的基礎上，傳遞函數原型模擬到數字的轉換傳遞函數進行了討論下一步。FIR數字濾波器的設計是在第 10章處理。在第 8 章，我們概述了為轉移的 FIR 和 IIR的各種功能的實現(xiàn)基本結構。該推算傳遞函數 G（ z）的過程稱為數字濾波器的設計。 IIR Digital Filter Design An important step in the development of a digital filter is the determination of a realizable transfer function G(z) approximating the given frequency response specifications. If an IIR filter is desired,it is also necessary to ensure that G(z) is stable. The process of deriving the transfer function G(z) is called digital filter design. After G(z) has been obtained, the next step is to realize it in the form of a suitable filter structure. In chapter 8,we outlined a variety of basic structures for the realization of FIR and IIR transfer functions. In this chapter,we consider the IIR digital filter design problem. The design of FIR digital filters is treated in chapter 10. First we review some of the issues associated with the filter design problem. A widely used approach to IIR filter design based on the conversion of a prototype analog transfer function to a digital transfer function is discussed next. Typical design examples are included to illustrate this approach. We then consider the transformation of one type of IIR filter transfer function into another type, which is achieved by replacing the plex variable z by a function of z. Four monly used transformations are summarized. Finally we consider the puteraided design of IIR digital filter. To this end, we restrict our discussion to the use of matlab in determining the transfer functions. preliminary considerations There are two major issues that need to be answered before one can develop the digital transfer function G(z). The first and foremost issue is the development of a reasonable filter frequency response specification from the requirements of the overall system in which the digital filter is to be employed. The second issue is to determine whether an FIR or IIR digital filter is to be designed. In the section ,we examine these two issues first . Next we review the basic analytical approach to the design of IIR digital filters and then consider the determination of the filter order that meets the prescribed specifications. We also discuss appropriate scaling of the transfer function. Digital Filter Specifications As in the case of the analog filter,either the magnitude and/or the phase(delay) response is specified for the design of a digital filter for most applications. In some situations, the unit sample response or step response may be specified. In most practical applications, the problem of interest is the development of a realizable approximation to a given magnitude response specification. As indicated in section , the phase response of the designed filter can be corrected by cascading it with an allpass section. The design of allpass phase equalizers has received a fair amount of attention in the last few years. We restrict our attention in this chapter to the magnitude approximation problem only. We pointed out in section that there are four basic types of filters,whose magnitude responses are shown in Figure . Since the impulse response corresponding to each of these is noncausal and of infinite length, these ideal filters are not realizable. One way of developing a realizable approximation to these filter would be to truncate the impulse response as indicated in Eq.() for a lowpass filter. The magnitude response of the FIR lowpass filter obtained by truncating the impulse response of the ideal lowpass filter does not have a sharp transition from passband to stopband but, rather, exhibits a gradual rolloff. Thus, as in the case of the analog filter design problem outlined in section , the magnitude response specifications of a digital filter in the passband and in the stopband are given with some acceptable tolerances. In addition, a transition band is specified between the passband and the stopband to permit the magnitude to drop off smoothly. For example, the magnitude )( ?jeG of a lowpass filter may be given as shown in Figure . As indicated in the figure, in the passband defined by 0 p???? , we require that the magnitude approximates unity with an error of p?? ,., ppjp fo reG ???? ? ????? ,1)(1. In the stopband, defined by ??? ??s ,we require that the magnitude approximates zero with an error of is,? .e., ,)(sjeG ?? ? for ??? ??s . The frequencies p? and s? are , respectively, called the passband edge frequency and the stopband edge frequency. The limits of the tolerances in the passband and stopband, p? and s? , are usually called the peak ripple values. Note that the frequency response