Datasheet

APPLICATIONINFORMATION
FULLYDIFFERENTIALAMPLIFIER
APPLICATIONSCHEMATICS
AdvantagesofFullyDifferentialAmplifiers
_
+
V
DD
V
O+
V
O-
GND
ToBattery
C
s
Bias
Circuitry
IN-
IN+
+
-
InFrom
DAC
SHUTDOWN
R
I
R
I
C
( )
BYPASS
(Optional)
R
F
R
F
TPA6205A1
www.ti.com
..............................................................................................................................................................SLOS490BJULY2006REVISEDJUNE2008
negativechannelsequallyandcancelsatthe
differentialoutput.However,removingthebypass
capacitorslightlyworsenspowersupplyrejection
TheTPA6205A1isafullydifferentialamplifierwith
ratio(k
SVR
),butaslightdecreaseofk
SVR
maybe
differentialinputsandoutputs.Thefullydifferential
acceptablewhenanadditionalcomponentcanbe
amplifierconsistsofadifferentialamplifieranda
eliminated(seeFigure17).
common-modeamplifier.Thedifferentialamplifier
BetterRF-immunity:GSMhandsetssavepower
ensuresthattheamplifieroutputsadifferential
byturningonandshuttingofftheRFtransmitterat
voltagethatisequaltothedifferentialinputtimesthe
arateof217Hz.Thetransmittedsignalis
gain.Thecommon-modefeedbackensuresthatthe
picked-uponinputandoutputtraces.Thefully
common-modevoltageattheoutputisbiasedaround
differentialamplifiercancelsthesignalmuch
V
DD
/2regardlessofthecommon-modevoltageatthe
betterthanthetypicalaudioamplifier.
input.
Inputcouplingcapacitorsnotrequired:AfullyFigure27throughFigure31showapplication
differentialamplifierwithgoodCMRR,liketheschematicsfordifferentialandsingle-endedinputs.
TPA6205A1,allowstheinputstobebiasedatTypicalvaluesareshowninTable1.
voltageotherthanmid-supply.Forexample,ifa
DAChasmid-supplylowerthanthemid-supplyofTable1.TypicalComponentValues
theTPA6205A1,thecommon-modefeedback
COMPONENTVALUE
circuitadjustsforthat,andtheTPA6205A1
R
I
10k
outputsarestillbiasedatmid-supplyofthe
R
F
10k
TPA6205A1.TheinputsoftheTPA6205A1can
bebiasedfrom0.5VtoV
DD
-0.8V.Iftheinputs
C
(BYPASS)
(1)
0.22µF
arebiasedoutsideofthatrange,inputcoupling
C
S
1µF
capacitorsarerequired.
C
I
0.22µF
Mid-supplybypasscapacitor,C
(BYPASS)
,not
(1)C
(BYPASS)
isoptional
required:Thefullydifferentialamplifierdoesnot
requireabypasscapacitor.Thisisbecauseany
shiftinthemid-supplyaffectsbothpositiveand
Figure27.TypicalDifferentialInputApplicationSchematic
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