Opera&onAmplifiers(OpAmps)
• Ac&vedevice,capableofprovidingvoltagegain
• Withproperconfigura&on,canimplementsumming,subtrac&on,integra&ononinputsignals
• Usedinnearlyeveryelectronicdevice
• Nearlyalwaysusedinafeedbackconfigura&on
+Differen&alinputs -
Single-endedOutput
V(+)
V(-)Vo
Feedback Network
i(+)
i(-)
• Wewilltreatthisdeviceasabuilding“block”withspecific(ideal)aJributesknownastheGOLDENRULESofOp-amps:
- Infiniteinputimpedanceonthe+and–terminalsi(+)=i(-)=0.
- VochangessothatV(+)=V(-)atall&mes…thismeanstheop-ampsourcesorsinkscurrentattheoutputterminalthroughthefeedbacknetworksothatV(+)=V(-).
Exampleofcircuitanalysiswithop-amps
Vout
RfRG
Vin
+15
-15
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp…Nowconsider:
Vout
Rf
RG
Vin
1. Usingouridealop-ampcharacteris&csfindanexpressionforVout/Vin
2. Whatopera&ondoesthisop-ampconfigura&onperform?
3. List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.
+15
-15
ENPH259GroupAc&vi&esforOct52017
Vout
Rf
RG
Vin
1. Usingouridealop-ampcharacteris&csfindanexpressionforVout/Vin
+15
-15
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp
ENPH259GroupAc&vi&esforOct52017
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp
ENPH259GroupAc&vi&esforOct52017
…Nowconsider:
Vout
Rf
RG
Vin
2. Whatopera&ondoesthisop-ampconfigura&onperform?
+15
-15
Actslikeanon-inver&ngamplifierwithgain>1
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp
ENPH259GroupAc&vi&esforOct52017
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandandEmilyorDavidwillcometohelp
Vout
Rf
RG
Vin
3. List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.
-15
Gainischanged
Gainischanged
ENPH259GroupAc&vi&esforOct82015PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp
ENPH259GroupAc&vi&esforOct52017
+15
Vout
Rf
RG
Vin
+15
-15
3. List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.
PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp
ENPH259GroupAc&vi&esforOct52017
15
Vout
RFRG
Vin
+15
-15
G =Vout
Vin
= �RF
RG
Twoofthemostimportantnon-idealaspectsofop-ampsare:
• Thegainisnotinfinite
• Themaximumgainwhichcanbeproducedisafunc&onoffrequency.Inotherwords,GdependsondrivefrequencyofVin
Hereisanexampleofanon-idealmodelofanOpAmpusingavoltage-dependentvoltagesource.
TheOpAmpcan’tmakeVoutarbitrarilylargebecauseAisnotinfinite.ThismeanstherewillalwaysbeasmallVd.
StartonPrelabfornextweekENPH259GroupAc&vi&esforOct52017
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