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对数放大器理想特性直线拟合算法分析
Introduction
Logarithmicamplifiers(logamps)areelectronicdevicesthatconverttheinputvoltagesignaltoalogarithmicallyproportionaloutputvoltage.Theyarecommonlyusedinaudioprocessing,powermeasurement,RFsignalprocessing,andotherapplications.Logamplifiersarewidelyacceptedfortheirexcellentlinearityoverawidedynamicrangeandawidebandwidth.Theyareusedinmanyapplicationssuchasopticalfibercommunication,powermetering,automaticgaincontrol(AGC),andthefront-endofanalog-to-digitalconverters(ADCs).
Theidealcharacteristicsofalogamplifierincludealinearoutputresponse,widebandwidth,andhighdynamicrange.Inreallife,however,logamplifiersarenotperfectandhavesomelimitations,includingquantizationnoise,limitedgain,temperaturedrift,andnonlinearity.Thesenon-idealcharacteristicscanbereducedbyusingvarioustechniques.
Thispaperpresentsanalgorithmforfittingtheidealcharacteristicsofalogamplifier.Thegoalistodevelopanalgorithmthatprovidesanaccuratefitoftheidealbehaviorofthelogamplifier.Thealgorithmwillbediscussedindetailinthefollowingsections.
TheIdealLogAmplifier
Inanideallogamplifier,theoutputvoltageisproportionaltothelogarithmoftheinputvoltage.Inotherwords,theoutputvoltageisgivenby:
Vout=KlogVin
whereKisaconstantandVinistheinputvoltage.TheconstantKdependsonthegainoftheamplifier.Theideallogamplifierhasthefollowingcharacteristics:
1.WideBandwidth–Theideallogamplifierhasawidebandwidththatisindependentoftheinputsignal.Thismeansthattheamplifiercanhandlesignalswithhighfrequencieswithoutdistortionorattenuation.
2.LargeDynamicRange–Theideallogamplifiercanhandlealargerangeofinputsignalswithoutsaturationorclipping.Thismeansthattheamplifiercanhandlebothsmallandlargesignalswithequalaccuracy.
3.LinearOutputResponse–Theideallogamplifierhasalinearoutputresponsethatisproportionaltotheinputsignal.Thismeansthattheamplifierprovidesanaccuraterepresentationoftheinputsignalwithoutanydistortionornonlinearities.
TheNon-IdealLogAmplifier
Inreal-lifelogamplifiers,severalnon-idealcharacteristicscanaffecttheperforman