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
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 References
6 External links
Linear circuit applications
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Operational amplifier applications - Wikipedia, the free encyclopedia
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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.
Differential Zin (between the two input pins) = R1 + R2
Differential amplifier
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)
Zin = Rin (because V - is a virtual ground)
A third resistor, of value
, added between the
non-inverting input and ground, while not necessary, minimizes
errors due to input bias currents.
Inverting amplifier
Non-inverting amplifier
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Amplifies a voltage (multiplies by a constant greater than 1)
(realistically, the input impedance of the op-amp itself,
1 MΩ to 10 TΩ)
A third resistor, of value
, added between the Vin source and the non-inverting
input, while not necessary, minimizes errors due to input bias
currents.
Non-inverting amplifier
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)
(realistically, the differential input impedance of the
op-amp itself, 1 MΩ to 1 TΩ)
Voltage follower
Summing amplifier
Sums several (weighted) voltages
When
, and Rf independent
Summing amplifier
When
Output is inverted
Input impedance Zn = Rn, for each input (V - is a virtual ground)
Integrator
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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.)
Integrating amplifier
Note that this can also be viewed as a type of electronic filter.
Differentiator
Differentiates the (inverted) signal over time.
The name "differentiator" should not be confused with the "differential
amplifier", also shown on this page.
Differentiating amplifier
(where Vin and Vout are functions of time)
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
Comparator
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
Is made by adding a non-inverting buffer to each input of the
differential amplifier to increase the input impedance.
Instrumentation amplifier
Schmitt trigger
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A comparator with hysteresis
Schmitt trigger
Inductance gyrator
Simulates an inductor.
Inductance gyrator
Zero level detector
Voltage divider reference
Zener sets reference voltage
Negative impedance converter (NIC)
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Creates a resistor having a negative value for any signal generator
In this case, the ratio between the input voltage and the input
current (thus the input resistance) is given by:
for more information see the main article Negative impedance converter.
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.
This basic configuration has some limitations. For more
information and to know the configuration that is actually used,
see the main article.
Super diode
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.
Peak detector
Logarithmic output
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The relationship between the input voltage vin and the output
voltage vout is given by:
Logarithmic configuration
where IS is the saturation current.
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
The relationship between the input voltage vin and the output
voltage vout is given by:
where IS is the saturation current.
Exponential configuration
Considering the operational amplifier ideal, then the negative pin is
virtually grounded, so the current through the diode is given by:
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when the voltage is greater than zero, it can be approximated by:
The output voltage is given by:
Other applications
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
Current-feedback operational amplifier
Operational transconductance amplifier
Frequency compensation
References
Paul Horowitz and Winfield Hill, "The Art of Electronics 2nd Ed. " Cambridge University Press,
Cambridge, 1989 ISBN 0-521-37095-7
Sergio Franco, "Design with Operational Amplifiers and Analog Integrated Circuits," 3rd Ed.,
McGraw-Hill, New York, 2002 ISBN 0-07-232084-2
External links
Introduction to op-amp circuit stages, second order filters, single op-amp bandpass filters, and a
simple intercom (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
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Operational amplifier applications - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Operational_amplifier_applications
(http://hyperphysics.phy-astr.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
Low Side Current Sensing Using Operational Amplifiers
(http://focus.ti.com/analog/docs/gencontent.tsp?familyId=57&genContentId=28017)
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/AN-30.pdf) PDF
Logarithmically variable gain from a linear variable component
(http://www.edn.com/archives/1994/030394/05di7.htm)
Retrieved from "http://en.wikipedia.org/wiki/Operational_amplifier_applications"
Categories: Electronic amplifiers | Integrated circuits
This page was last modified 16:54, 16 January 2007.
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