Operational amplifier applications - Wikipedia, the free encyclopedia
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Operational amplifier applications
From Wikipedia, the free encyclopedia
This article illustrates some typical applications of solid-state integrated circuit operational amplifiers. A
simplified schematic notation is used, and the reader is reminded that many details such as device selection
and power supply connections are not shown.
The resistors used in these configurations are typically in the kΩ range. <1 kΩ range resistors cause excessive
current flow and possible damage to the device. >1 MΩ range resistors cause excessive thermal noise and
make the circuit operation susceptible to significant errors due to bias currents.
Note: It is important to realize that the equations shown below, pertaining to each type of circuit, assume that
it is an ideal op amp. Those interested in construction of any of these circuits for practical use should consult
a more detailed reference. See the External links and References sections.
Contents
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1 Linear circuit applications
„ 1.1 Differential amplifier
„ 1.1.1 Amplified difference
„ 1.1.2 Difference amplifier
„ 1.2 Inverting amplifier
„ 1.3 Non-inverting amplifier
„ 1.4 Voltage follower
„ 1.5 Summing amplifier
„ 1.6 Integrator
„ 1.7 Differentiator
„ 1.8 Comparator
„ 1.9 Instrumentation amplifier
„ 1.10 Schmitt trigger
„ 1.11 Inductance gyrator
„ 1.12 Zero level detector
„ 1.13 Negative impedance converter (NIC)
2 Non-linear configurations
„ 2.1 Precision rectifier
„ 2.2 Peak detector
„ 2.3 Logarithmic output
„ 2.4 Exponential output
3 Other applications
4 See also
5 External links
6 References
Linear circuit applications
Differential amplifier
The circuit shown is used for finding the difference of two voltages each multiplied by some constant
(determined by the resistors).
The name "differential amplifier" should not be confused with the "differentiator", also shown on this page.
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Differential Zin (between the two input pins) = R1 + R2
Amplified difference
Whenever R1 = R2 and Rf = Rg,
Difference amplifier
When R1 = Rf and R2 = Rg (including previous conditions, so that R1 = R2 = Rf = Rg):
Inverting amplifier
Inverts and amplifies a voltage (multiplies by a negative constant)
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Zin = Rin (because V − is a virtual ground)
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Non-inverting amplifier
Amplifies a voltage (multiplies by a constant greater than 1)
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(realistically, the input impedance of the op-amp itself, 1 MΩ to 10 TΩ)
Voltage follower
Used as a buffer amplifier, to eliminate loading effects or to interface impedances (connecting a device with a
high source impedance to a device with a low input impedance)
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(realistically, the differential input impedance of the op-amp itself, 1 MΩ to 1 TΩ)
Summing amplifier
Sums several (weighted) voltages
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Output is inverted
Input impedance Zn = Rn, for each input (V − is a virtual ground)
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, and Rf independent
Integrator
Integrates the (inverted) signal over time
(where Vin and Vout are functions of time, Vinitial is the output voltage of the integrator at time t = 0.)
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Note that this can also be viewed as a type of electronic filter.
yh
Differentiator
Differentiates the (inverted) signal over time.
The name "differentiator" should not be confused with the "differential amplifier", also shown on this page.
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(where Vin and Vout are functions of time)
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Note that this can also be viewed as a type of electronic filter.
Comparator
Compares two voltages and outputs one of two states depending on which is greater
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See article for details
Instrumentation amplifier
Combines very high input impedance, high common-mode rejection, low DC offset, and other properties used
in making very accurate, low-noise measurements
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Is made by adding a non-inverting buffer to each input of the differential amplifier to increase the input
impedance.
See article for details
Schmitt trigger
A comparator with hysteresis
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See article for details
Inductance gyrator
Simulates an inductor
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See article for details
Zero level detector
Voltage divider reference
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Zener sets reference voltage
Negative impedance converter (NIC)
Creates a resistor having a negative value for any signal generator
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In this case, the ratio between the input voltage and the input current (thus the input resistance) is given
by:
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for more information see the main article Negative impedance converter.
Non-linear configurations
Precision rectifier
Behaves like an ideal diode for the load, which is here represented by a generic resistor RL.
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This basic configuration has some limitations. For more information and to know the configuration that
is actually used see the main article.
Peak detector
When the switch is closed, the output goes to zero volts. When the switch is opened for a certain time interval,
the capacitor will charge to the maximum input voltage attained during that time interval.
The charging time of the capacitor must be much shorter than the period of the highest appreciable frequency
component of the input voltage.
Logarithmic output
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The relationship between the input voltage vin and the output voltage vout is given by:
where IS is the saturation current.
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If the operational amplifier is considered ideal, the negative pin is virtually grounded, so the current
flowing into the resistor from the source (and thus through the diode to the output, since the op-amp
inputs draw no current) is:
where ID is the current through the diode. As known, the relationship between the current and the voltage for
a diode is:
This, when the voltage is greater than zero, can be approximated by:
Putting these two formulae together and considering that the output voltage Vout is the inverse of the voltage
across the diode VD, the relationship is proven.
Note that this implementation does not consider temperature stability and other non-ideal effects.
Exponential output
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The relationship between the input voltage vin and the output voltage vout is given by:
where IS is the saturation current.
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Considering the operational amplifier ideal, then the positive pin is virtually grounded, so the current
through the diode is given by:
when the voltage is greater than zero, it can be approximated by:
The output voltage is given by:
Other applications
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audio and video pre-amplifiers and buffers
voltage comparators
differential amplifiers
differentiators and integrators
filters
precision rectifiers
voltage regulator and current regulator
analog-to-digital converter
digital-to-analog converter
voltage clamps
oscillators and waveform generators
Schmitt trigger
Gyrator
Comparator
Active filter
Analog computer
See also
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Current-feedback operational amplifier
Operational transconductance amplifier
Frequency compensation
External links
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Introduction to op-amp circuit stages, second order
filters, single op-amp bandpass filters, and a simple
intercom
Wikibooks has more about this
subject:
Electronics/Op-Amps
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(http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm)
Op Amps for Everyone (http://focus.ti.com/lit/an/slod006b/slod006b.pdf) (PDF)
A table of standard applications (http://www.rfcafe.com/references/electrical/opamps.htm)
Hyperphysics - descriptions of common applications (http://hyperphysics.phyastr.gsu.edu/hbase/electronic/opampvar.html)
Single supply op-amp circuit collection
(http://instruct1.cit.cornell.edu/courses/bionb440/datasheets/SingleSupply.pdf) (PDF)
Op-amp circuit collection (http://www.national.com/an/AN/AN-31.pdf) (PDF)
A Collection of Amp Applications
(http://www.analog.com/UploadedFiles/Application_Notes/28080533AN106.pdf) (PDF) — Analog
Devices Application note
Basic OpAmp Applications (http://www.ligo.caltech.edu/~vsanni/ph5/BasicOpAmpApplications.pdf)
(PDF)
HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS
(http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf) (PDF) — Texas Instruments Application note
Logarithmic amplifier (http://www.play-hookey.com/analog/logarithmic_amplifier.html)
Precision half-wave rectifier (http://www.play-hookey.com/analog/half-wave_rectifier.html)
Precision full-wave rectifier (http://www.play-hookey.com/analog/full-wave_rectifier.html)
Log/anti-log generators, cube generator, multiply/divide amp (http://www.national.com/an/AN/AN30.pdf) (PDF)
Logarithmically variable gain from a linear variable component
(http://www.edn.com/archives/1994/030394/05di7.htm)
References
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Paul Horowitz and Winfield Hill, "The Art of Electronics 2nd Ed. " Cambridge University Press,
Cambridge, 1989 ISBN 0-521-37095-7
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Sergio Franco, "Design with Operational Amplifiers and Analog Integrated Circuits," 3rd Ed.,
McGraw-Hill, New York, 2002 ISBN 0-07-232084-2
Retrieved from "http://en.wikipedia.org/wiki/Operational_amplifier_applications"
Categories: Electronic amplifiers | Integrated circuits
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This page was last modified 03:28, 23 September 2006.
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