新型CCII电流传输器.doc

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1、NewCCIICurrentConveyorBy:JohnRobinsonMar27,2008Abstract:Offeringhigherbandwidththanitsvoltage-feedbackcounterpart,thesecond-generationcurrentconveyoroperationalamplifier(CCII)canbeusedinRFmixers,high-frequencyprecisionrectifiers,andmedicalapplicationssuchaselectricalimpedancetomography.Thec

2、onventionaloperationalamplifierscannotbeusedinthehigh-frequencyapplicationsduetotheirlimitedgain-bandwidthproduct.IntroductionThecurrentconveyorhasbeenaroundsincetheoriginaldesign,orCCI(whichcanberegardedasanidealtransistor),wasinitiallyproposedbySmithandSedrain1968¹,².CCIwasthenreplacedbya

3、moreversatilesecond-generationdevicein1970,theCCII³.CurrentconveyordesignshavemainlybeenBJTduetotheirhightransconductancevaluescomparedtotheirCMOScounterparts.Theyareusedascurrent-feedbackoperationalamplifierssuchastheMAX4223low-poweramplifier,whichfeaturescurrentfeedbackratherthantheconven

4、tionalvoltagefeedbackusedbystandardoperationalamplifiers.Thismeansthatthecurrentfeedbackoperationalamplifierisnotrestrictedbytheconventionalgainbandwidthsofastandardoperationalamplifier,andcanofferamuchhigherbandwidthsolutionthanitsvoltage-feedbackcounterpart.Currentconveyorsareusedinhigh-f

5、requencyapplicationswheretheconventionaloperationalamplifierscannotbeused,becausetheconventionaldesignsarelimitedbytheirgain-bandwidthproduct.Intheory,thecurrentconveyorisonlylimitedbytheftofthetransistorsusedinitsdesign.SomeapplicationswherecurrentconveyorsareusedtodayincludeRFmixers,high-

6、frequencyprecisionrectifiers,andmedicalapplicationssuchasElectricalImpedanceTomography(EIT).ABipolarConveyorThediagraminFigure1belowshowsacurrentconveyorimplementedusingbipolardevices.Figure1.AbipolarCCII.FromFigure1itcanbeseenthattheCCIIconveyorcanbemodelledasanidealtransistor:Ybeingthebas

7、e/gateXbeingtheemitter/sourceZbeingthecollector/drainThistypeofcircuitworkswellasacircuitwithBJTs,asthetransconductanceandEarlyvoltagesofBJTsaremuchgreaterthanthatofCMOSdevices.Therefore,currentconveyorsworkwellassourcefollowers.GainX/Yiscloseto1;Zhasana