opamp pesentation

8/14/2019 opamp pesentation

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Definition:Definition:

An opamp is a direct coupled highAn opamp is a direct coupled highgain differential amplifier. It is a versatilegain differential amplifier. It is a versatiledevice. It can be used as an AC and DCdevice. It can be used as an AC and DC

input signal.input signal.It is basically used for mathematicalIt is basically used for mathematicaloperations like addition, subtraction,operations like addition, subtraction,

differentiation, integration etcdifferentiation, integration etc


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Block diagram of Op-Amp [a 741]:Block diagram of Op-Amp [a 741]:

Input stage Intermediate

stage

Level

transistorOutput stage

Noninverting i/p

Inverting i/p

Dual input

balanced

outputdifferentiator

amplifier

Dual input

unbalanced

output

differentiatoramplifier

Emitter follower

Complementary

push pull

amplifier

output


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An opamp is a direct coupled high gain differential amplifier. It consistsAn opamp is a direct coupled high gain differential amplifier. It consists

of one or two difference amplifier followed by level transistor and an outputof one or two difference amplifier followed by level transistor and an output

stage.stage.The input stage is a dual input balanced. Output differential amplifier whichThe input stage is a dual input balanced. Output differential amplifier which

provides voltage gain of establishes high input impedance of the opamp.provides voltage gain of establishes high input impedance of the opamp.

The intermediate stage is another dual input unbalanced outputThe intermediate stage is another dual input unbalanced output

differential amplifier which provides the output which is parallel to the firstdifferential amplifier which provides the output which is parallel to the first

stage. This stage is driven by output of the first stage.stage. This stage is driven by output of the first stage.

Both the input and intermediate stage are direct coupled, due to this DCBoth the input and intermediate stage are direct coupled, due to this DC

voltage at output of intermediate stage is above ground level. Therefore avoltage at output of intermediate stage is above ground level. Therefore a

level transistor is used to shift the Dc level and the output of the intermediatelevel transistor is used to shift the Dc level and the output of the intermediate

stage to zero volts with respect to ground level, for this an emitter follower isstage to zero volts with respect to ground level, for this an emitter follower is

used.used.


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SYMBOL OF Op-AmpSYMBOL OF Op-Amp

An opamp has two inputs and one output terminal. TheAn opamp has two inputs and one output terminal. The

ve terminal is called inverting terminal and +ve ve terminal is called inverting terminal and +veterminal is called non inverting terminal.terminal is called non inverting terminal.

The output is the difference between two input terminalThe output is the difference between two input terminal

V=V0=V2-V1V=V0=V2-V1

+Vcc

-Vee

Output

Inverting terminal

Non inverting terminal


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Characteristics of opamp {ideal}:Characteristics of opamp {ideal}:

input impedance = {Ri=}input impedance = {Ri=} output impedance = 0 { Ro= 0}output impedance = 0 { Ro= 0} infinite voltage gain = {Av=}infinite voltage gain = {Av=}

Characteristics do not drift with temperature.Characteristics do not drift with temperature. perfect balance when V1=V2 when V0=0perfect balance when V1=V2 when V0=0 Infinite common mode rejection ratioInfinite common mode rejection ratio


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Parameters of Op-AmpParameters of Op-Amp

Input offset voltage {Vio}Input offset voltage {Vio} Input offset current {Iio}Input offset current {Iio} Output offset voltageOutput offset voltage

Common mode rejection ratioCommon mode rejection ratio GainGain

Power supply rejection ratioPower supply rejection ratio bandwidth productbandwidth product Output impedanceOutput impedance

Input impedance Zi or RiInput impedance Zi or Ri


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Input offset voltage {Vio}:Input offset voltage {Vio}:

Input offset voltage is that voltage which must be appliedInput offset voltage is that voltage which must be appliedbetween input terminals to balance the amplifier.between input terminals to balance the amplifier.

Input offset current {Iio}:Input offset current {Iio}:

Input offset current is the difference between the currents entersInput offset current is the difference between the currents entersthe input terminal of the balanced amplifier.the input terminal of the balanced amplifier.

Output offset voltage:Output offset voltage:

It is the difference between two DC voltages present at twoIt is the difference between two DC voltages present at twooutput terminals when two input terminals are grounded.output terminals when two input terminals are grounded.

Common mode rejection ratio:Common mode rejection ratio:

It is defined s the ratio of differential voltage gain Ad to theIt is defined s the ratio of differential voltage gain Ad to thecommon mode voltage gain Ac.common mode voltage gain Ac.

It is denoted by {Et}It is denoted by {Et}==


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Gain:Gain:

It is the ratio of output voltage to difference of twoIt is the ratio of output voltage to difference of twoinput voltage.input voltage.

Av=V0/VdAv=V0/VdAv=V0/ (V2-V1)Av=V0/ (V2-V1)

Power supply rejection ratio:Power supply rejection ratio:

It is the ratio of change in an opamp input offsetIt is the ratio of change in an opamp input offsetvoltage. Vio to variation in supply voltage is calledvoltage. Vio to variation in supply voltage is called

power supply rejection ratio.power supply rejection ratio.

It is expressed in v/ (micro volts/ohm}It is expressed in v/ (micro volts/ohm}PSRR=Vio/V v/PSRR=Vio/V v/

Bandwidth product:Bandwidth product:

It is the product of bandwidth of the opamp whenIt is the product of bandwidth of the opamp whenvoltage gain is unity.voltage gain is unity.


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Input impedance Zi or Ri:Input impedance Zi or Ri:

It is the total resistance betweenIt is the total resistance between

inverting and non inverting inputs.inverting and non inverting inputs.Output impedance:Output impedance:

It is the equivalent resistance i.e. measuredIt is the equivalent resistance i.e. measured

between output terminal and ground.between output terminal and ground.


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Applications of Op-AmpApplications of Op-Amp Inverting amplifierInverting amplifier

Non inverting amplifierNon inverting amplifier Voltage followerVoltage follower Summing amplifierSumming amplifier

Difference amplifierDifference amplifier DifferentiatorDifferentiator IntegratorIntegrator ComparatorComparator Zero crossing detector and peak detectorZero crossing detector and peak detector Window comparatorWindow comparator MultivibratorMultivibrator

Active filterActive filter


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Inverting amplifierInverting amplifier

Inverting amplifier is one in which the output is 180 out ofInverting amplifier is one in which the output is 180 out of

phase with the input. Here the input signal is applied to invertingphase with the input. Here the input signal is applied to invertingterminal and non inverting terminal is grounded. Rf is called asterminal and non inverting terminal is grounded. Rf is called asfeed back resistor.feed back resistor.

Since the voltage gain and input impedance are infiniteSince the voltage gain and input impedance are infinite

virtual ground exists between inverting and non invertingvirtual ground exists between inverting and non invertingterminal therefore junction A is called summing point.terminal therefore junction A is called summing point.Apply kcl at point A Apply kcl at point A i+if=0i+if=0i = -ifi = -if(Vi-0) /Rs=(0-V0) /Rf(Vi-0) /Rs=(0-V0) /RfV1/Rs = -Vo/RfV1/Rs = -Vo/RfV0/V1= -Rf/RsV0/V1= -Rf/RsAv= -Rf/RsAv= -Rf/Rs

The ve sign implies that the output is 80out phase with input.The ve sign implies that the output is 80out phase with input.


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Circuit & Wave Form Of Inverting AmplifierCircuit & Wave Form Of Inverting Amplifier

t

t

Vi

Vo


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Non invertintg amplifierNon invertintg amplifier

A Non inverting amplifier is one in which the outputA Non inverting amplifier is one in which the outputis in phase with the input. Here the input signal is applied to nonis in phase with the input. Here the input signal is applied to noninverting terminal and the inverting terminal is fed with the feedinverting terminal and the inverting terminal is fed with the feed

back resistor Rf.back resistor Rf.Apply kcl at point AApply kcl at point A

-i-if=0-i-if=0-i=if-i=ifi=-ifVi/Rs= (V1-V0)/Rfi=-ifVi/Rs= (V1-V0)/RfV1/Rs= (-Vi/Rf) + (V0/Rs)V1/Rs= (-Vi/Rf) + (V0/Rs)V1/Rs+V1/Rf=V0/RfV1/Rs+V1/Rf=V0/RfV1 [1/Rs+1/Rf] =V0/RfV1 [1/Rs+1/Rf] =V0/RfV1/V0= [Rs+Rf]/RfV1/V0= [Rs+Rf]/RfV1/V0=Rs/Rs+Rf/RfV1/V0=Rs/Rs+Rf/RfV0/V1=1+ (Rf/Rf)V0/V1=1+ (Rf/Rf)


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Summing amplifierSumming amplifier

A summing amplifier using opamp it is one whichA summing amplifier using opamp it is one whichadds two or more inputs. The input voltage are applied toadds two or more inputs. The input voltage are applied toinverting terminal and non inverting terminal is gnd. Due toinverting terminal and non inverting terminal is gnd. Due tovirtual gnd i.e. because of infinite input impedance and infinitevirtual gnd i.e. because of infinite input impedance and infinitevoltage gain point a is held at zero potential.voltage gain point a is held at zero potential.

Apply kcl at node AApply kcl at node A

I1+I2-If=0I1+I2-If=0I1+I2=IfI1+I2=IfV1/R1+V2/R2= (0-Vf)/RfV1/R1+V2/R2= (0-Vf)/RfV1/R1+V2/R2=-Vf/RfV1/R1+V2/R2=-Vf/Rf

Assume R1=R2=RF=RAssume R1=R2=RF=R(V1+V2)R=-V0/R(V1+V2)R=-V0/RV0=-(V1+V2)V0=-(V1+V2)The ve sign implied that the input voltage is fed to invertingThe ve sign implied that the input voltage is fed to inverting

terminalterminal


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Difference amplifier:Difference amplifier:It is one whose output is the difference of one or more input.It is one whose output is the difference of one or more input.

Assume V2=0, A=0, B=0Assume V2=0, A=0, B=0Apply Kcl at Node AApply Kcl at Node AI1-I2=0I1-I2=0V1/R1=-VO/R2 -------->1V1/R1=-VO/R2 -------->1

Assume V1=0 A=0 B=0Assume V1=0 A=0 B=0Apply kcl at node AApply kcl at node AI1-I2=0I1-I2=0V2/R1=0/R2V2/R1=0/R2V2/R1=0 -------->2V2/R1=0 -------->2Subtract 1 from 2Subtract 1 from 2V2/R1-V1/R1=V0/R2V2/R1-V1/R1=V0/R2R1=R2=RR1=R2=RV2-V1=0V2-V1=0

V2/R1-V1/R1=0-(-V0)/R2V2/R1-V1/R1=0-(-V0)/R2


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Voltage FollowerVoltage Follower

Fig shows a voltage follower circuit. A voltage follower isFig shows a voltage follower circuit. A voltage follower isone in which the output voltage follower the input voltage.one in which the output voltage follower the input voltage.

The input voltage is applied to non inverting terminal andThe input voltage is applied to non inverting terminal andinverting terminal is directly shorted to output terminal due toinverting terminal is directly shorted to output terminal due to

infinite input impedance and infinite voltage gain the invertinginfinite input impedance and infinite voltage gain the invertingterminal is also held at Vi.terminal is also held at Vi.

Therefore output voltage is equal to the input voltage i.e. V0=Vi.Therefore output voltage is equal to the input voltage i.e. V0=Vi.Since no resistors are used gain of the voltage follower is equalSince no resistors are used gain of the voltage follower is equal

to unity.to unity.


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DifferentiatorDifferentiatorA Differentiator produces an output voltage which is directlyA Differentiator produces an output voltage which is directly

proportional to derivative of input voltage.proportional to derivative of input voltage.Fig shows a Differentiator circuit which uses an RC network. TheFig shows a Differentiator circuit which uses an RC network. Thethrough the capacitor is given by I=Cdvi/dt and current through thethrough the capacitor is given by I=Cdvi/dt and current through theresistor r is given by If=-V0/R due to virtual gnd at the opamp input.resistor r is given by If=-V0/R due to virtual gnd at the opamp input.

I=IfI=If

Dvi/dt=-V0/RDvi/dt=-V0/RV0=-RCdvi/dtV0=-RCdvi/dt

Therefore V0dvi/dtTherefore V0dvi/dt

The ve sign implies that the signal is connected to invertingThe ve sign implies that the signal is connected to invertingterminal.terminal.

Vi =vc=Q/cVi =vc=Q/cVi =Q/cVi =Q/c

Vi = (1/c)QVi = (1/c)Q

dvi/dt = 1/c (dq/dt)dvi/dt = 1/c (dq/dt)

dvi/dt = i/cdvi/dt = i/c

i=cdvi/dti=cdvi/dt


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Circuit & Wave Form Of DifferentiatorCircuit & Wave Form Of Differentiator

t

t

Vi

Vo


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IntegratorIntegrator

A Integrator is one whose output voltage is directlyproportional to the integral of input voltage.

Current through the resistor is given byI= (Vin/R)Current through the capacitor is

If = -C(dVout/dt)Due to the virtual ground at the inputI=If(Vin/R) = -C(dVout/dt)

dVout = -(Vin/RC)dtby integrating the above equation we getVout is directly proportional to the integral of Vin-ve sign indicates that input voltages are fed to inverting terminal


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Circuit & Wave Form Of IntegratorCircuit & Wave Form Of Integrator

Vi

Vo


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ComparatorComparator

It is a circuit which compares a signalIt is a circuit which compares a signalvoltage at one input of an opamp with a knownvoltage at one input of an opamp with a knownreference voltage at the other input.reference voltage at the other input.

Comparator is basically an open loop opamp withComparator is basically an open loop opamp withoutput equals to +/-Vsatoutput equals to +/-Vsat

There are basically two types of comparator s nonThere are basically two types of comparator s non

inverting and inverting comparators.inverting and inverting comparators.


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Inverting comparator with +ve RefInverting comparator with +ve Ref

Fig shows an inverting comparator with +ve reFig shows an inverting comparator with +ve revoltage.voltage.Here inverting terminal is supplied with input signal andHere inverting terminal is supplied with input signal and

non inverting terminal with known ref voltage.non inverting terminal with known ref voltage.

When Vin< Vref then V0 = +Vsat because the nonWhen Vin< Vref then V0 = +Vsat because the noninverting terminal voltage is greater than invertinginverting terminal voltage is greater than invertingterminal voltage.terminal voltage.

When Vin > Vref then V0 = -Vsat because the invertingWhen Vin > Vref then V0 = -Vsat because the invertingterminal voltage is greater than non inverting terminalterminal voltage is greater than non inverting terminalvoltage.voltage.

When Vin = Vref the transistor takes places from +Vsat toWhen Vin = Vref the transistor takes places from +Vsat to-Vsat.-Vsat.


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Circuit & Waveforms Of InvertingCircuit & Waveforms Of InvertingComparator With +Ve RefComparator With +Ve Ref

t

t

Vi

Vo


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Inverting comparator with Ve RefInverting comparator with Ve Ref

Figure shows an inverting comparator with veFigure shows an inverting comparator with vereference voltage. The input signal is applied toreference voltage. The input signal is applied toinverting terminal and known reference voltage isinverting terminal and known reference voltage isapplied to non-inverting terminal.applied to non-inverting terminal.

When Vi-Vr then Vo=-Vsat because inverting

terminal voltage is greater than non inverting terminalterminal voltage is greater than non inverting terminal

voltage.voltage.When Vi=Vr the transition takes place from VsatWhen Vi=Vr the transition takes place from Vsat

to +Vsatto +Vsat

i i f f i


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Circuit & Waveforms Of InvertingCircuit & Waveforms Of InvertingComparator With -Ve RefComparator With -Ve Ref

t

t

Vi

Vo


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Non Inverting [+ve Ref]Non Inverting [+ve Ref]

The fig shows non inverting comparator with +veThe fig shows non inverting comparator with +veref. The input is applied to non inverting terminal andref. The input is applied to non inverting terminal andreference voltage is applied to inverting terminal. Whenreference voltage is applied to inverting terminal. When

Vi< Vr, V0 = -Vsat because the inverting terminalVi< Vr, V0 = -Vsat because the inverting terminalvoltage is greater then non inverting. When Vi> Vr,voltage is greater then non inverting. When Vi> Vr,V0= Vsat because the non inverting terminal voltage isV0= Vsat because the non inverting terminal voltage isgreater than inverting terminal.greater than inverting terminal.

i i f f iCi i & W f Of N I i


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Circuit & Waveforms Of Non InvertingCircuit & Waveforms Of Non InvertingComparator With +Ve RefComparator With +Ve Ref

t

t

Vi

Vo


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Non Inverting [-ve Ref]Non Inverting [-ve Ref]

The fig shows non invertingThe fig shows non invertingcomparator with -ve ref. The input is applied tocomparator with -ve ref. The input is applied tonon inverting terminal and reference voltage isnon inverting terminal and reference voltage is

applied to inverting terminal. When Vi< Vr, V0applied to inverting terminal. When Vi< Vr, V0= Vsat because the non inverting terminal= Vsat because the non inverting terminalvoltage is greater than inverting. When Vi> Vr,voltage is greater than inverting. When Vi> Vr,V0= Vsat because the inverting terminal voltageV0= Vsat because the inverting terminal voltageis greater than non inverting terminal.is greater than non inverting terminal.


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Astable multivibratorAstable multivibrator

A multivibrator which generates square waveA multivibrator which generates square waveof its own is called astable multivibrator.of its own is called astable multivibrator.An astable multivibrator output frequencyAn astable multivibrator output frequency

depends on charging and discharging of adepends on charging and discharging of acapacitor. There is no input signal to thiscapacitor. There is no input signal to thismultivibrator.multivibrator.Initially assume that the output is in +veInitially assume that the output is in +ve

saturation +Vsat. The voltage at non invertingsaturation +Vsat. The voltage at non invertingterminal becomesterminal becomes

Vlt=(R2/R1+R2)+VsatVlt=(R2/R1+R2)+Vsat


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So capacitor starts charging exponentially towardsSo capacitor starts charging exponentially towards+Vsat as shown by solid arrows. But never reaches to+Vsat as shown by solid arrows. But never reaches to+Vsat because once the capacitor voltage reaches just+Vsat because once the capacitor voltage reaches just

above Vlt the output switches from +Vsat to Vsat.above Vlt the output switches from +Vsat to Vsat.Now the ve voltage isNow the ve voltage is

Vlt=(R2/R1+R2) VsatVlt=(R2/R1+R2) VsatIt is fed back to the non inverting input. Now theIt is fed back to the non inverting input. Now the

capacitor starts discharging from +Vlt to zero voltscapacitor starts discharging from +Vlt to zero voltscompletely and recharges towards Vsat in the reversecompletely and recharges towards Vsat in the reversedirection as shown by the dotted arrows.direction as shown by the dotted arrows.When the capacitor voltage reaches just below theWhen the capacitor voltage reaches just below thelower trigger voltage Vlt then the output switches backlower trigger voltage Vlt then the output switches backfrom Vsat to +Vsat. Thus because of continuousfrom Vsat to +Vsat. Thus because of continuouscharging and discharging of capacitor the output ischarging and discharging of capacitor the output is asquare wave with 50% duty cycle.square wave with 50% duty cycle.


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The time period is given byThe time period is given by

T = 2Rc ln(1+T = 2Rc ln(1+/1-)/1-)

Where --->RWhere --->R22/(R/(R11+R+R22))The frequency of output wave form is given byThe frequency of output wave form is given by

F = 1/TF = 1/T

t

t

Vi

Vo


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