www.德州仪器.com
分析器
20 hz − 20 khz
(一个) 基本 class−ab
APA
信号
发生器
电源 供应
分析器
20 hz − 20 khz
R
L
(b) 过滤-自由 和 traditional 类-d
类-dAPA
信号
发生器
电源 供应
R
L
低-通过 rc
过滤
低-通过 rc
过滤
(一个)
(一个)
为 efficiency 度量 和 过滤-自由 类-d, r
L
应当 是 一个 inductive 加载 像 一个 扬声器.
DIFFERENTIALINPUTANDBTLOUTPUT
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
figure21.audiomeasurementsystems
thetpa3008d2usesamodulationschemethatdoesnotrequireanoutputfilterforoperation,buttheydo
sometimesrequireanrclow-passfilterwhenmakingmeasurements.thisisbecausesomeanalyzerinputs
cannotaccuratelyprocesstherapidlychangingsquare-waveoutputandthereforerecordanextremelyhighlevel
ofdistortion.therclow-passmeasurementfilterisusedtoremovethemodulatedwaveformssotheanalyzer
canmeasuretheoutputsinewave.
alloftheclass-dapasandmanyclass-abapashavedifferentialinputsandbridge-tiedload(btl)输出.
differentialinputshavetwoinputpinsperchannelandamplifythedifferenceinvoltagebetweenthepins.
differentialinputsreducethecommon-modenoiseanddistortionoftheinputcircuit.btlisatermcommonly
usedinaudiotodescribedifferentialoutputs.btloutputshavetwooutputpinsprovidingvoltagesthatare180
degreesoutofphase.theloadisconnectedbetweenthesepins.thishastheaddedbenefitsofquadruplingthe
outputpowertotheloadandeliminatingadcblockingcapacitor.
ablockdiagramofthemeasurementcircuitisshowninfigure22.thedifferentialinputisabalancedinput,
meaningthepositive(+)andnegative(-)pinshavethesameimpedancetoground.similarly,thebtloutput
equatestoabalancedoutput.
21
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