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时间:2018-07-06
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1、Topic2.4–AnalogueCommunications.2.4.3MixingSignals.LearningObjectives:Attheendofthistopicyouwillbeableto;þdrawacircuitforamixerbasedonanop-ampsummingamplifier;þusethegainformulatocalculatetheoutputvoltageforagivensummingamplifiercircuit.5Topic2.4–AnalogueCommunications.2.4.3MixingSignals.2.
2、4.3MixingSignalsAmixercircuitisanimportantpartofmanyaudiosystems.ForexampleDJ’suseamixerto‘voiceover’records.Recordingstudiosusemixerstobalancethesoundfromdifferentvoicesandinstruments.SummingAmplifierThebasicbuildingblockofamixerisaninvertingamplifier,configuredasasummingamplifierinwhichtw
3、oormoreinputsareused.Considerthecircuitshownbelow.Thecircuitiscalledasummingamplifierbecauseitaddsthevoltagesateachofitsinputstogether.Youwillrememberforaninvertingamplifier:Forasummingamplifier,thiscanberewrittenas:IfR1=R2=RINthen:5Topic2.4–AnalogueCommunications.2.4.3MixingSignals.Whatist
4、helimitationofthissummingamplifierifitistobeusedasamixer?…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………AtwoChannelMixerThesummingamplifierprovidesthebasisforamixercircuitinwhichtwoormoreinputsignalscanbemixedtogetherandfadedinorout
5、independentlyofoneanother.Atwochannelmixercircuitisshownbelow.·PotentiometersVR1andVR2areusedattheinputofeachchanneltoindependentlycontrolthefadinginoroutofeachchannel.ForexampleifyouconsiderSignal1,whenthewiperisatthetopofVR1,thewholeofsignal1passesintothesummingamplifier.Asthewipermovesto
6、wards0V,lessandlessofsignal1appearsatV1,andthesignalfadesoutprogressivelyuntilthewiperreaches0V.·Theremainderofthecircuitintheblueboxisjustasummingamplifierasdescribedonthepreviouspage.Wewillnowinvestigatesummingamplifiersandmixercircuits.5Topic2.4–AnalogueCommunications.2.4.3MixingSignals.
7、Activity1:UsingtheoperationalamplifierasasummingamplifierInformation:Wehaveseenthatforthesummingamplifiershownbelowwithtwoequalinputresistors:1a.Setupthefollowingcircuit,withinputresistorsof1kΩandafeedbackresistorof10kΩ.YoucanobtainthevariablevoltagesV1,
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