www.德州仪器.com
C
i
在
Z
i
Z
f
输入
信号
f
1
2
Z
i
C
i
(4)
inputcapacitor,c
i
f
c
1
2
Z
i
C
i
-3 db
f
c
(5)
C
i
1
2
Z
i
f
c
(6)
POWERSUPPLYDECOUPLING
TPA3007D1
SLOS418A–SEPTEMBER2003–REVISEDDECEMBER2004
这-3-dbfrequencycanbecalculatedusingequation4.usetable2forz
i
值.
inthetypicalapplicationaninputcapacitor(c
i
)isrequiredtoallowtheamplifiertobiastheinputsignaltothe
properdclevelforoptimumoperation.inthiscase,c
i
andtheinputimpedanceoftheamplifier(z
i
)forma
高-passfilterwiththecornerfrequencydeterminedinequation5.
ThevalueofC
i
isimportant,asitdirectlyaffectsthebass(lowfrequency)performanceofthecircuit.考虑
theexamplewhereZ
i
is241k
Ω
andthespecificationcallsforaflatbassresponsedownto20hz.equation5is
reconfiguredasequation6.
inthisexample,c
i
is33nf,soonewouldlikelychooseavalueof0.1µf,asthisvalueiscommonlyused.ifthe
gainisknownandwillbeconstant,usez
i
fromTable2tocalculateC
i
.afurtherconsiderationforthiscapacitor
istheleakagepathfromtheinputsourcethroughtheinputnetwork(c
i
)andthefeedbacknetworktotheload.
thisleakagecurrentcreatesadcoffsetvoltageattheinputtotheamplifierthatreducesusefulheadroom,
especiallyinhighgainapplications.forthisreasonalow-leakagetantalumorceramiccapacitoristhebest
选择.whenpolarizedcapacitorsareused,thepositivesideofthecapacitorshouldfacetheamplifierinputin
mostapplicationsasthedclevelthereisheldat2.5v,whichislikelyhigherthanthesourcedclevel.notethatit
isimportanttoconfirmthecapacitorpolarityintheapplication.
thetpa3007d1isahigh-performancecmosaudioamplifierthatrequiresadequatepowersupplydecoupling
toensuretheoutputtotalharmonicdistortion(thd)isaslowaspossible.powersupplydecouplingalso
preventsoscillationsforlongleadlengthsbetweentheamplifierandthespeaker.theoptimumdecouplingis
achievedbyusingtwocapacitorsofdifferenttypesthattargetdifferenttypesofnoiseonthepowersupplyleads.
forhigherfrequencytransients,尖刺,ordigitalhashontheline,agoodlowequivalent-序列-阻抗(等效串联电阻)
ceramiccapacitor,typically1µfplacedascloseaspossibletothedevicev
CC
leadworksbest.forfiltering
更小的-frequencynoisesignals,alargeraluminumelectrolyticcapacitorof10µforgreaterplacedneartheaudio
poweramplifierisrecommended.
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