ADC选型与基本原理(TI).ppt

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1、ADCselectionandBasicprinciplesBasicprinciples采样过程是通过模拟电子开关S实现的。模拟电子开关每隔一定的时间间隔闭合次，当一个连续的模拟信号通这个电子开关时，就会转换若干个离散的脉冲信号。输入模拟电压uiCP取样展宽信号ui′SADC电子开关S受CP控制...Dn-1D1D0ADC的量化编码电路N位数字量输出通过采样脉冲的作用，转换成时间上离散、但幅值上仍连续的离散模拟信号。量化编码就是先将幅值连续可变的采样信号量化成幅值有限的离散信号，再将这些离散信号用对应量化电平的一组二进制代码表示。uiInputsignalw

2、aveformsamplingcircuitDiscretesamplingcircuitoutputwaveformtuSamplingIntervalTimeSampleHoldingTimeBasicsampled-datasystemsThefigureshowsatypicalsampleddataDSPsystemblockdiagram.Theactualanalog-to-digitalconversion,analogsignalusuallymustgothroughcertaintypesofsignalconditioningcircuits,t

3、hesesignalstoperformasamplification,attenuation,andfilteringsuchfunctions.Requireslow-pass/bandpassfiltertounwantedsignalseliminatedfromtheusefulbandwidth,andcanpreventtheoccurrenceofaliasing.1.SamplingandkeepingSamplingTheorem(Nyquist‘sLaw):asignalwithabandwidthfmustbesampledatarate>2,o

4、rinformationaboutthesignalwillbelost.Ifthesamplingfrequencylessthantwicethebandwidthoftheanalogsignal,aliasingphenomenonappears.usually,=(3~5)Quantizationandcoding1.Quantization:Digitalsignal,notonlyintimeisdiscrete,butalsonumericalvalueofthechangeisnotcontinuous.Thatthesizeofanydigitali

5、sonlyacertainspecifiedminimumnumberofintegerunits.Therefore,beforeA/Dconversionmustalsobesampledvoltageintothesmallestintegralmultipleofthenumberofunits,theconversionprocessisknownas"quantitative."2.coding:Thequantizedsignalwiththecorrespondingquantizationlevelofabinarycodetorepresentthe

6、processcalledencoding.QuantifythevoltagedifferencebetweenthetwoiscalledquantizationintervalS,themedianquantitativevoltagemorefinerquantizationlevel,Svalueswillbecome.Eg:To01Vanalogvoltageforthethreebinaryencoding.Analogvoltage0V1/8V2/8V3/8V4/8V5/8V6/8V7/8V1VBinarycode0000010100111001011

7、10111Codecorrespondingtothediscretelevelsimulation0ε→0V1ε→1/8V2ε→2/8V3ε→3/8V4ε→4/8V5ε→5/8V6ε→6/8V7ε→7/8VWecansee，themaximumquantizationerrorisε=1/8V。Classification1.SAR（逐次逼近）型ADC：逐次比较型AD由一个比较器和DA转换器通过逐次比较逻辑构成，从MSB开始，顺序地对每一位将输入电压与内置DA转换器输出进行比较，经n次比较而输出数字值。其电路规模属于中等。其优点是速度较