elt2_2
DESCRIPTION
nTRANSCRIPT
![Page 1: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/1.jpg)
Leah M. Akins, DCC 1
Unit 2: Introduction toOperational Amplifiers
by Leah M. Akinsbased on Operational
Amplifiers and LinearIntegrated Circuits by
Coughlin & Driscoll
![Page 2: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/2.jpg)
Leah M. Akins, DCC 2
Analog and Digital Systems The first op-amps were used for
performing operations in an analogenvironment:èaddition and subtractionèmultiplication and divisionèintegration and differentiation.
These operations are now performed withgreater speed, accuracy, and versatilitywithin a digital environment.
Did this do the op-amp in?
![Page 3: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/3.jpg)
Leah M. Akins, DCC 3
Current Op-AmpApplications
“As more digital systems are created fordata acquisition and process control,more interface circuits using op-ampsand other linear integrated circuits arealso required.” C&D, p. 2.
Op-Amp Applicationsèsignal conditioningèA/D and D/A conversionèfiltersèoscillators …. And much more.
![Page 4: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/4.jpg)
Leah M. Akins, DCC 4
Circuit Symbol andTerminals
-
741
+
InvertingInput, V-
Non-InvertingInput, V+
PositiveSupply, VCC
NegativeSupply,VEE
Output,Vo
Pin 3
Pin 2
Pin 7
Pin 4
Pin 6
![Page 5: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/5.jpg)
Leah M. Akins, DCC 5
Internal Op-Amp Circuitry(see figure 1-3 or handout)
Input Stage - Differential AmplifierèIts characteristics are very high input
impedance and large voltage gain.
Intermediate Stage - Level ShifterèOutput of the differential amplifier is directly
coupled to the intermediate stage. Itsfunction is to pass the signal unaltered whileshifting its dc voltage level to a value requiredto bias the output stage.
![Page 6: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/6.jpg)
Leah M. Akins, DCC 6
Internal Op-Amp Circuitry(cont.)
Output Stage - Push-Pull AmplifierèA pnp-npn push-pull amplifier configuration s
used as the output stage. This gives the op-amp its characteristic low output impedance.
Packaging and PinoutsèPackaging: see figure 1-4èPinouts: see figure 1-5
Breadboarding Suggestions : read 1-6.2
![Page 7: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/7.jpg)
Leah M. Akins, DCC 7
Op-Amp Terminals(see figure 2-1 or handout)
power supply terminals: +V and -V output terminal: Vo
input terminals: V+ and V-
input resistance: Rin
output resistance: Ro
input bias currents: I+ and I- differential voltage: Ed = V+ - V-
![Page 8: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/8.jpg)
Leah M. Akins, DCC 8
Open Loop Voltage Gain
Aol, the open loop voltage gain, isthe voltage gain supplied whenthere is no negative feedback fromoutput back to input.
General Amplifier Equation: Vo = AvVin
Operational Amplifier Equation:Vo = Aol Ed
![Page 9: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/9.jpg)
Leah M. Akins, DCC 9
Typical vs. Ideal Values The table below compares some
typical values for an operationalamplifier along with the ideal values.
Description Typical Value Ideal ValueOpen loop gain 200,000 Infinite
Input resistance 2 MΩΩ Infinite, opencircuit
Input biascurrents
80 nA 0 A
Input offsetvoltage
1 mV 0 V
![Page 10: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/10.jpg)
Leah M. Akins, DCC 10
Significance of Real versusIdeal Value
The input offset voltage, Vos, is acharacteristic of the real op-amp.
Input offset does not occur in theideal device because thedifferential amplifier in the inputstage is made from perfectlymatched transistors.
Any mismatch in the differentialamplifier results in an input offset.
![Page 11: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/11.jpg)
Leah M. Akins, DCC 11
Effect of Offset Voltage
Consider that both inputs are equal, sothat Ed=0.èIdeally, Vo = Aol Ed = 0.èIn reality, the input offset voltage is also
amplified so thatVo = Aol Vos = 200,000 (1mV) = 200V !
Even with no input, the output is driven toits highest possible value as limited by thepower supply of the circuit.
![Page 12: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/12.jpg)
Leah M. Akins, DCC 12
The Limits
The output voltage can never exceed thepower supply voltages. See fig. 2-3.èIn a real op amp, the output is usually limited
to a value slightly less than the power supplyvoltage due to internal voltage drops. Seeinternal circuitry.èSaturation voltages are specified on the
manufacturer’s data sheet.èFor a 741 Op-Amp using +/- 15V supplies:
» +Vsat =14V and -Vsat = -13V
![Page 13: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/13.jpg)
Leah M. Akins, DCC 13
Open Loop Applications
Zero-Crossing Detector - fig. 2-4 Positive Voltage Level Detector - fig. 2-5 Negative Voltage Level Detector - fig. 2-6 Typical Applications of Voltage-Level
Detectorsèsee sections 2-5, 2-7, and 2-8èdiscuss
![Page 14: Elt2_2](https://reader035.vdocument.in/reader035/viewer/2022072001/563db7d3550346aa9a8e4a08/html5/thumbnails/14.jpg)
Leah M. Akins, DCC 14
The End Readèchapter 3, C & D
HWèConsider figures 2-4, 2-5, and 2-6 and how
you would implement them on Multisim.
Lab ActivityèTest for existence of offset.èConstruct variety of op amp level detectors.