Operational amplifier

Operational amplifier

1. Operational
Amplifiers
By Unsa Shakir

2. What is an Op-Amp
Lowcostintegratingcircuitconsistingof:
•Transistors
•Resistors
•Capacitors
Abletoamplifyasignalduetoanexternal
powersupply
Namederivesfromitsusetoperform
operationsonasignal.

3. Applications of Op-Amps
Simple Amplifiers
Summers
Comparators
Integrators
Differentiators
Analog to Digital Converters

4. Circuit Symbol and Pin Identification
2 Inverting Input
3 Non-Inverting Input
6 Output
7 + Voltage Supply
V
CC
4 –Voltage Supply
V
EE
1 and 5 --Offset NullU1
741
3
2
4
7
6
51

5. What do they really look like?

6. IC Circuit

7. Op-Amp “Golden Rules”
•Whenanop-ampisconfiguredinanynegative-
feedbackarrangement,itwillobeythefollowingtwo
rules:
–Theinputstotheop-ampdraworsourceno
current(truewhethernegativefeedbackornot)
–Theop-ampoutputwilldowhateveritcan(within
itslimitations)tomakethevoltagedifference
betweenthetwoinputszero

8. Inverting Amplifier
R
R
F
V
in
i
in
i
out
CR
R
V
V
F
in
out


9. Non-Inverting Amplifier
R
R
F
i
in
i
out
C
V
inR
R
1
V
V
F
in
out


10. Summing Circuits
•Usedtoaddanalogsignals
•Voltageaveragingfunction
intosummingfunction
Calculate closed loop gain for
each input1
1
R
R
A
f
CL

 2
1
R
R
A
f
CL

 3
1
R
R
A
f
CL

 CLnino AVV  3
3
2
2
1
1
R
R
V
R
R
V
R
R
VV
fff
o
  
321 VVVV
o 
Ifallresistorsareequalinvalue:

11. Difference Circuit
•Usedtosubtractanalog
signals
•Output signal is
proportionaltodifference
betweentwoinputs12VVV
out 
If all resistors are equal: 
1
31
124
4132
)( R
RV
RRR
RRRV
V
out





12. Integrating Circuit
•Replacefeedbackresistorof
invertingop-ampwithcapacitor
•Aconstantinputsignal
generatesacertainrateof
changeinoutputvoltage
•Smoothessignalsovertime

13. Differentiating Circuit
•Inputresistorofinvertingop-
ampisreplacedwithacapacitor
•Signalprocessingmethod
whichaccentuatesnoiseover
time
•Outputsignalisscaled
derivativeofinputsignal

14. Comparator Circuit
•Determinesifonesignalisbiggerthananother
•Nonegativefeedback,infinitegainandcircuitsaturates
•Saturation:outputismostpositiveormostnegativevalue
V
1is V
ref
V
2is V
in

15. Analog to Digital Converters
Anelectronicintegratedcircuitwhichtransformsasignalfrom
analog(continuous)todigital(discrete)form.
Microprocessorscanonlyperformcomplexprocessingondigitized
signals.
Whensignalsareindigitalformtheyarelesssusceptibletothe
deleteriouseffectsofadditivenoise.
ADCProvidesalinkbetweentheanalogworldoftransducersand
thedigitalworldofsignalprocessinganddatahandling.
SomeexamplesofADCusagearedigitalvoltmeters,cellphone,
thermocouples,anddigitaloscilloscope.

16. How ADC works ?
Mainly there are two steps for the analog to digital conversion:
S/H: Sampling and holding
Q/E: Quantizing and Encoding
The ADC process is shown in figure below:

17. Sampling & Holding
•Itisusedtosamplethegiveninputsignalandtoholdthe
sampledvalue.Onceasignalissampled,itiscalleda
discretesignal.
•Sampleandholdcircuitisusedtosampleananalogsignal
forashortintervaloftimeintherangeof1to10µSandto
holdonitslastsampledvalueuntiltheinputsignalis
sampledagain.
•Theholdingperiodmaybefromafewmillisecondsto
severalseconds.

18. Quantization and Encoding
Theoutputofasamplerisstillcontinuousinamplitude.To
transmitasadigitalsignalwemustrestrictthenumberof
possiblevalues.
Quantizationistheprocessof“roundingoff”asampledvalue
accordingtosomerule.
–E.g.supposewemustroundtothenearesttenth,then:
3.752-->3.80.001-->0
Encoding:Afteridentifyingtheclosestvalue,anumerical
valueisassignedtoitanditisencodedintheformofabinary
number.