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BASICMEASUREMENTSYSTEM
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
thisapplicationnotefocusesonmethodsthatusethebasicequipmentlistedbelow:
•
Audioanalyzerorspectrumanalyzer
•
digitalmultimeter(dmm)
•
Oscilloscope
•
twisted-pairwires
•
Signalgenerator
•
powerresistor(s)
•
Linearregulatedpowersupply
•
Filtercomponents
•
EVMorothercompleteaudiocircuit
figure21showstheblockdiagramsofbasicmeasurementsystemsforclass-abandclass-damplifiers.asine
waveisnormallyusedastheinputsignalbecauseitconsistsofthefundamentalfrequencyonly(noother
harmonicsarepresent).ananalyzeristhenconnectedtotheapaoutputtomeasurethevoltageoutput.这
analyzermustbecapableofmeasuringtheentireaudiobandwidth.aregulateddcpowersupplyisusedto
reducethenoiseanddistortioninjectedintotheapathroughthepowerpins.asystemtwoaudiomeasurement
系统(ap-ii)(reference1)byaudioprecisionincludesthesignalgeneratorandanalyzerinonepackage.
thegeneratoroutputandamplifierinputmustbeac-结合.不管怎样,theevmsalreadyhavetheac-连接
电容,(c
在
),sonoadditionalcouplingisrequired.thegeneratoroutputimpedanceshouldbelowtoavoid
attenuatingthetestsignal,andisimportantbecausetheinputresistanceofapasisnothigh.相反地,这
分析器-inputimpedanceshouldbehigh.theoutputimpedance,r
输出
,oftheapaisnormallyinthehundreds
ofmilliohmsandcanbeignoredforallbutthepower-relatedcalculations.
figure21(一个)showsaclass-abamplifiersystem.ittakesananalogsignalinputandproducesananalogsignal
输出.thisamplifiercircuitcanbedirectlyconnectedtotheap-iiorotheranalyzerinput.
thisisnottrueoftheclass-damplifiersystemshowninfigure21(b),whichrequireslow-passfiltersinmost
casesinordertomeasuretheaudiooutputwaveforms.thisisbecauseittakesananaloginputsignaland
convertsitintoapulse-widthmodulated(pwm)outputsignalthatisnotaccuratelyprocessedbysome
analyzers.
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