Laboratory1Differentialamplifiers;measuringtheperformanceofadifferentialamplifier;

Twostagedifferentialamplifier;ACcoupleddifferentialamplifierAlexPatriciumodifiedbyHubertdeBruinandLauraPravato

Scopeofthelab:

⎯ Introducethefundamentalpropertiesofdifferentialamplifiers⎯ Presentthemeasurementofcommonmodegain;CMRR;CMR⎯ IllustratetheeffectofDCbiasonamplifiedsignal⎯ Analyzethepropertiesofamulti-stageinstrumentationamplifier⎯ BecomefamiliarwithMacECEBiomedLabplatform.

Beforethelab:

1. ReviewtheschematicsofathreeOP-AMPdifferentialamplifier.ReviewthecomputationofCMMR.2. DownloadandreadthedocumentationfortheinstrumentationamplifierLT1920andforthe

operationalamplifierTLC2274.3. Reviewthepassivefilterstheory;reviewtheactivefilterstheory.

Objectivesduringthelab:

A. IdentifythedifferentcomponentsoftheMacECEBiomedLabplatform1. Identifythedifferentmodulesontheboard(instrumentationstage,HPfilterstage,notchfilterstage

etc.)2. Identifythebreadboardmodule3. Identifytheisolationamplifier

B. Measuretheamplifiergainandcompareitwiththetheoreticalone.

1. Usinga5.5kΩresistor,buildtheinstrumentationamplifieronstage1oftheboard.Thiswillamplifytheinputsignalbyagainof10(GDifferential=10).

2. Connecttheinputoftheinstrumentationamplifiertothesignalgeneratorandtheoutputtotheoscilloscope.UsethesettingspresentedinFigure1.

3. ComputethetheoreticalgainofthesignalandverifythatthesignaldisplayedontheoscilloscopehastheamplitudeGDifferential*inputsignalamplitude.

4. WithoutchangingtheinstrumentsettingsconnectthecircuitasinFigure2.5. Whatistheamplitudeofthesignalnow?Whataboutitsphase?6. Repeatthemeasurementsfor100Hz,1kHz,10kHz,100kHz,500kHz,600kHz,700kHz.7. Plotthemeasuredgainasafunctionoffrequency.

Figure1:Schematicformeasuringnon-invertinggain.

Figure2:Schematicformeasuringinvertinggain.

C. MeasuretheCMRR1. ConnecttheequipmentasshowninFigure3.2. SettheinputasshowninFigure3.(100Hz,3Vpp).Thiswillbeyourcommonmodevoltage.3. Measurethecommonmodeoutputvoltageandexplainwhatishappening.4. Calculatethecommonmodegain:GCM=VoutCM/VinCM.5. CalculatethecommonmoderejectionratioCMRR=GDifferential/GCMandCMR(dB)=20log10(CMRR)6. Repeatthemeasurementsfor100Hz,1kHz,10kHz,100kHz,500kHz,600kHz,700kHz.7. PlotthemeasuredCMMRasafunctionoffrequency.

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Figure3:Schematicformeasuringcommonmodegain

D. Addthesecondamplificationstage

1. Addasecondamplificationstagewithagainof11tothedifferentialamplifierasshowninFigure4.UsetheTLC2274.Whatisthenewgainofthecircuit?

2. Generateasinusoidalsignalwith>20mVp-pamplitudeand100Hzfrequency.Usethenon-invertinginput(Figure2)andverifythecorrectgain.

3. Repeatthemeasurements100Hz,1kHz,10kHz,100kHz,500kHz,600kHz,700kHz.4. Plotthegainversusfrequency.Explainwhatishappening.

Figure4:Instrumentationamplifierwithsecondamplificationstage.

E. StudytheeffectofaDCoffsetontheoutput.

1. Setthesignalgeneratortoaddanoffsetof20mVtothesinusoidalsignal.2. Whatdoestheoutputsignallooklike?Explainwhatisgoingon.3. DCoffsetsmaybepresentinbiomedicalsignals.Whatcanyoudotoremovethem?

F. BiomedicalAmplifierwithfirst-orderHPandLPfilters1. InsertapassiveHPandanactiveLPfilterinthebiomedicalamplifierasshowninFigure5.Calculate

thecomponentvaluessothatyouachieveaband-passfilterwithcutoff-frequenciesof1.5Hzand400Hz.

2. Generateasinusoidalsignalwith10mVp-pamplitudeand100Hzfrequencyand20mVDCoffset.Connectthebiomedicalamplifiertothesignalgeneratorandtotheoscilloscope.

3. Whatdoesyouroutputlooklike?4. Verifythatthehigh-passfiltereffectivelyremovestheDCcomponentfromtheinputsignal.

Figure5:InstrumentationamplifierwithHPFandLPF.

LabReport

– Dueoneweekafteryoudoyourlab.– Prepareaformallabreportwiththequestions/calculations/plotsrequiredbyquestions:

o B3.B5.B7.o C3.C4.C5.C7.o D1.D4.o E2.E3.o F1.F3.