餐饮业会计做账流程.doc

Abstract
DTMF is used in modern dialing systems Because it is more faster and reliable than pulse dialel s,has already been used with the automatic telephone system addition,Ⅱcan be widely used for transmission in such information as various kinds of datafiows and voice,etc in the dala colrllrtunication system DTMF generator and receiver IC aFe ponent ol、the signal transmission generator of DTMF call generate 1 6 pairs of DTMF signal,the receiver can reject unwanted signals and magnify the DTMF signals
In the text,the operation principle of DTMF generator and receiver has been generator and the most important parts of receiver have been article makes a detailed analysis and expatiation for the operational principle and design technique of switched
··capacitors--filtenThe bandpass filter are derived from swithch··capacitor,And plish the simulation using u m process,obtaining satisfying result The results of MPW(multi project wafer)indicate that all the aesigned specifications have been satisfied
Key words DTMF,DAC,SCF
筇一章引言
DTMF的发展历史和研究现状
DTMF信号是将拨号需上的O~9、A~D及*/E、#/r共16个字符,川音频范的8个频率米表示的‘种编自日方-℃。8个频率分为高卿!群和低频群两绀,分别作为列顺利行频。高频肝的杯准佰分别为:1209Hz,1336Hz,1477Hz,1633Hz。低频群的标准值为 697Hz,770Hz,852Hz,941Hz。每个字符的信号由来白列频和行频的两个频率的止弦信寸叠加而成。
、卜述标准频率的选定不是任选的,而是设计时考虑了拨号音、忙音及交流电源的杂音, 这些杂音均不住上述DTMF信号的范隔内。同时为了避免标准频率之间的潴波干扰 现, 故所列最高标准频率小r晟低标准频率的_次谐波川。
早j5【I的DTMF接收器是利用成排的带通滤波器来实现的,显得笨拙且价格昂贵,冈此其府IL}J范吲受到了限制。第一'fEDTMF接收器是南Lc滤波器、有源滤波器和锁相环技术来接收干¨解码的,这样的接收器充当话音剑脉冲的转换器。随着MOS人规模集成Lb路的发展, 出现了第一代DTMF接收器,它用模拟带通滤波器将接收刨的音频信号分丌,然后刚数字电路进{亍解码。
开关电容滤波器的出现产生了第ZqEDt'I_lF接收器,开芙电容滤波器是由MOS运放、MOS 模拟开关和电棒等基本部件所组成的,它具有体积小、功耗低、调试方便等优点。另外,由丁二升关电容滤波器的时间常数是由两个电容的比值术决定的,与电容的绝对值的大小无关, 而MOS集成}%,且温度系数较低,使得滤波器的性能比较稳定。另外,开关电容滤波器是在时钟信号作用一p f作的,/。便地凋挣滤波器的频率},。正是由J‘开关电容滤波器具仃这Ⅱ;优点, 所咀可以将扦天电容滤波器单独集成成一块芯片,而解码部分也单独集成在块芯片。这样,
~个以往比较复杂的DTN+接收器便可山两块芯片组成,这就是第二三代DTM“妾收器的思想。【艺水平和设计水平的4:断提高,使利将模拟
电路手¨数宁【