数控放大器

LFto750MHz,DigitallyControlledVGAAD8370Rev.AInformationfurnishedbyAnalogDevicesisbelievedtobeaccurateandreliable.However,noresponsibilityisassumedbyAnalogDevicesforitsuse,norforanyinfringementsofpatentsorotherrightsofthirdpartiesthatmayresultfromitsuse.Specificationssubjecttochangewithoutnotice.NolicenseisgrantedbyimplicationorotherwiseunderanypatentorpatentrightsofAnalogDevices.Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.OneTechnologyWay,P.O.Box9106,Norwood,MA02062-9106,U.S.A.Tel:[phone]©2005AnalogDevices,Inc.Allrightsreserved.FEATURESProgrammablelowandhighgain(2dBresolution)Lowrange:−11dBto+17dBHighrange:6dBto34dBDifferentialinputandoutput200Ωdifferentialinput100Ωdifferentialoutput7dBnoisefigure@maximumgainTwo-toneIP3of35dBm@70MHz−3dBbandwidthof750MHz40dBprecisiongainrangeSerial8-bitdigitalinterfaceWideinputdynamicrangePower-downfeatureSingle3Vto5VsupplyAPPLICATIONSDifferentialADCdriversIFsamplingreceiversRF/IFgainstagesCableandvideoapplicationsSAWfilterinterfacingSingle-ended-to-differentialconversionGENERALDESCRIPTIONTheAD8370isalowcost,digitallycontrolled,variablegainamplifier(VGA)thatprovidesprecisiongaincontrol,highIP3,andlownoisefigure.TheexcellentdistortionperformanceandwidebandwidthmaketheAD8370asuitablegaincontroldeviceformodernreceiverdesigns.Forwideinput,dynamicrangeapplications,theAD8370providestwoinputranges:highgainmodeandlowgainmode.Avernier,7-bit,transconductance(gm)stageprovides28dBofgainrangeatbetterthan2dBresolutionand22dBofgainrangeatbetterthan1dBresolution.Asecondgainrange,17dBhigherthanthefirst,canbeselectedtoprovideimprovednoiseperformance.TheAD8370ispoweredonbyapplyingtheappropriatelogicleveltothePWUPpin.Whenpowereddown,theAD8370consumeslessthan4mAandoffersexcellentinputtooutputisolation.Thegainsettingispreservedwhenoperatinginapower-downmode.FUNCTIONALBLOCKDIAGRAMINHIINLOOPHIOPLOVCCOOCOMICOMVOCMPWUPVCCOOCOMVCCIICOMBIASCELLSHIFTREGISTERANDLATCHESPREAMPTRANSCONDUCTANCEOUTPUTAMP11611641413125983210715DATACLCKLTCHAD837003692-001Figure1.010203040506070–30–20–10010203040VOLTAGEGAIN(dB)VOLTAGEGAIN(V/V)0102030406010050708090110120130GAINCODE03692-002CODE=LAST7BITSOFGAINCODE(NOMSB)HIGHGAINMODEHIGHGAINMODELOWGAINMODELOWGAINMODEΔGAINΔCODE≅0.409ΔGAINΔCODE≅0.059Figure2.Gainvs.GainCodeat70MHzGaincontroloftheAD8370isthroughaserial8-bitgaincontrolword.TheMSBselectsbetweenthetwogainranges,andtheremaining7bitsadjusttheoverallgaininpreciselineargainsteps.FabricatedontheADIhighspeedXFCBprocess,thehighbandwidthoftheAD8370provideshighfrequencyandlowdistortion.ThequiescentcurrentoftheAD8370is78mAtypically.TheAD8370amplifiercomesinacompact,thermallyenhanced16-leadTSSOPpackageandoperatesoverthetemperaturerangeof−40°Cto+85°C.AD8370Rev.A|Page2of28TABLEOFCONTENTSFeatures..............................................................................................1Applications.......................................................................................1GeneralDescription.........................................................................1FunctionalBlockDiagram..............................................................1RevisionHistory...............................................................................2Specifications.....................................................................................3AbsoluteMaximumRatings............................................................5ESDCaution..................................................................................5PinConfigurationandFunctionDescriptions.............................6TypicalPerformanceCharacteristics.............................................7TheoryofOperation......................................................................13BlockArchitecture......................................................................13Preamplifier.................................................................................13TransconductanceStage............................................................13OutputAmplifier........................................................................14DigitalInterfaceandTiming....................................................14Applications.....................................................................................15BasicConnections......................................................................15GainCodes..................................................................................15Power-UpFeature.......................................................................15ChoosingBetweenGainRanges..............................................16LayoutandOperatingConsiderations....................................16PackageConsiderations.............................................................17Single-Ended-to-DifferentialConversion...............................17DC-CoupledOperation.............................................................18ADCInterfacing..........................................