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时间:2018-07-09
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1、Topic2.4–AnalogueCommunications.2.4.3MixingSignals.LearningObjectives:Attheendofthistopicyouwillbeableto;þdrawacircuitforamixerbasedonanop-ampsummingamplifier;þusethegainformulatocalculatetheoutputvoltageforagivensummingamplifiercircuit.5Topic2.4–AnalogueC
2、ommunications.2.4.3MixingSignals.2.4.3MixingSignalsAmixercircuitisanimportantpartofmanyaudiosystems.ForexampleDJ’suseamixerto‘voiceover’records.Recordingstudiosusemixerstobalancethesoundfromdifferentvoicesandinstruments.SummingAmplifierThebasicbuildingbloc
3、kofamixerisaninvertingamplifier,configuredasasummingamplifierinwhichtwoormoreinputsareused.Considerthecircuitshownbelow.Thecircuitiscalledasummingamplifierbecauseitaddsthevoltagesateachofitsinputstogether.Youwillrememberforaninvertingamplifier:Forasumminga
4、mplifier,thiscanberewrittenas:IfR1=R2=RINthen:5Topic2.4–AnalogueCommunications.2.4.3MixingSignals.Whatisthelimitationofthissummingamplifierifitistobeusedasamixer?…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
5、………………………………AtwoChannelMixerThesummingamplifierprovidesthebasisforamixercircuitinwhichtwoormoreinputsignalscanbemixedtogetherandfadedinoroutindependentlyofoneanother.Atwochannelmixercircuitisshownbelow.·PotentiometersVR1andVR2areusedattheinputofeachchannel
6、toindependentlycontrolthefadinginoroutofeachchannel.ForexampleifyouconsiderSignal1,whenthewiperisatthetopofVR1,thewholeofsignal1passesintothesummingamplifier.Asthewipermovestowards0V,lessandlessofsignal1appearsatV1,andthesignalfadesoutprogressivelyuntilthe
7、wiperreaches0V.·Theremainderofthecircuitintheblueboxisjustasummingamplifierasdescribedonthepreviouspage.Wewillnowinvestigatesummingamplifiersandmixercircuits.5Topic2.4–AnalogueCommunications.2.4.3MixingSignals.Activity1:Usingtheoperationalamplifierasasummi
8、ngamplifierInformation:Wehaveseenthatforthesummingamplifiershownbelowwithtwoequalinputresistors:1a.Setupthefollowingcircuit,withinputresistorsof1kΩandafeedbackresistorof10kΩ.YoucanobtainthevariablevoltagesV1,
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