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C
在
音频的 电源
放大器
发生器
Low−Pass
rc 过滤
C
在
R
GEN
R
GEN
R
在
R
在
V
GEN
R
输出
R
输出
分析器
R
ANA
R
ANA
C
ANA
Low−Pass
rc 过滤
R
L
C
ANA
Twisted-一双 线
evaluation 单元
Twisted-一双 线
类-drclow-passfilter
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
figure22.differentialinput,btloutputmeasurementcircuit
thegeneratorshouldhavebalancedoutputs,andthesignalshouldbebalancedforbestresults.anunbalanced
outputcanbeused,butitmaycreateagroundloopthataffectsthemeasurementaccuracy.theanalyzermust
alsohavebalancedinputsforthesystemtobefullybalanced,therebycancellingoutanycommon-modenoisein
thecircuitandprovidingthemostaccuratemeasurement.
thefollowinggeneralrulesshouldbefollowedwhenconnectingtoapaswithdifferentialinputsandbtloutputs:
•
useabalancedsourcetosupplytheinputsignal.
•
useananalyzerwithbalancedinputs.
•
usetwisted-pairwireforallconnections.
•
useshieldingwhenthesystemenvironmentisnoisy.
•
ensurethatthecablesfromthepowersupplytotheapa,andfromtheapatotheload,canhandlethelarge
电流(seetable2).
table2showstherecommendedwiresizeforthepowersupplyandloadcablesoftheapasystem.thereal
concernisthedcoracpowerlossthatoccursasthecurrentflowsthroughthecable.theserecommendations
arebasedon12-inchlongwirewitha20-khzsine-wavesignalat25
°
c.
table2.recommendedminimumwiresizeforpowercables
DCPOWERLOSSACPOWERLOSS
P
输出
(w)r
L
(
Ω
)awgsize
(mw)(mw)
104182216401842
2418223.283.78.5
182228282.18.1
<0.75822281.56.11.66.2
anrcfilterisusedtoreducethesquare-waveoutputwhentheanalyzerinputscannotprocessthepulse-宽度
modulatedclass-doutputwaveform.thisfilterhaslittleeffectonthemeasurementaccuracybecausethecutoff
frequencyissetabovetheaudioband.thehighfrequencyofthesquarewavehasnegligibleimpacton
measurementaccuracybecauseitiswellabovetheaudiblefrequencyrange,andthespeakerconecannot
respondatsuchafastrate.thercfilterisnotrequiredwhenanlclow-passfilterisused,suchaswiththe
类-dapasthatemploythetraditionalmodulationscheme(tpa032d0x,tpa005dxx).
thecomponentvaluesofthercfilterareselectedusingtheequivalentoutputcircuitasshowninfigure23.r
L
istheloadimpedancethattheapaisdrivingforthetest.theanalyzerinputimpedancespecificationsshouldbe
availableandsubstitutedforR
ANA
andC
ANA
.thefiltercomponents,r
FILT
andC
FILT
,canthenbederivedforthe
系统.thefiltershouldbegroundedtotheapaneartheoutputgroundpinsoratthepowersupplygroundpin
tominimizegroundloops.
22
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