Instrumentation amplifiers are analog subsystems that amplify low-level signals in the presence of high common mode noise. These differential amplifiers are optimized for DC signals and are typically characterized by high gain, high input impedance, and high common mode rejection ratio (CMRR). The most commonly used instrumentation amplifiers include two or three operational amplifiers and several precisely matched resistors. The use of multiple operational amplifiers improves both gain linearity and accuracy. In these devices, CMRR is approximately equal to half the resistor mismatch plus the gain. The output or common mode error is fixed by the resistor mismatch and independent of both the gain and the output signal. Instrumentation amplifiers that include only a single operational amplifiers are also available, but do not achieve the low drift and low bias currents of more advanced devices. Device specifications for instrumentation amplifiers include the number of analog channels and the number of differential channels. When single-ended outputs are available, suppliers often specify the maximum number of analog channel outputs as twice the number of differential outputs. Differential channels, which have two inputs, define the voltage as the signal to process between the two inputs. Other device specifications for instrumentation amplifiers include maximum output voltage, gain range, and input impedance. Gain, the factor by which input signals are multiplied, is frequently greater than unity; however, gain can be fractional when a reduction (attenuation) of signal amplitude is desired. Impedance, the resistance to alternating signal flow, is a result of the resistance, capacitance, and inductance of a device’s circuitry. For instrumentation amplifiers, input impedance is typically specified as much greater than the impedance of the devices whose signals are amplified.
Instrumentation amplifiers are analog subsystems that amplify low-level signals in the presence of high common mode noise. These differential amplifiers are optimized for DC signals and are typically characterized by high gain, high input impedance, and high common mode rejection ratio (CMRR). The most commonly used instrumentation amplifiers include two or three operational amplifiers and several precisely matched resistors. The use of multiple operational amplifiers improves both gain linearity and accuracy. In these devices, CMRR is approximately equal to half the resistor mismatch plus the gain. The output or common mode error is fixed by the resistor mismatch and independent of both the gain and the output signal. Instrumentation amplifiers that include only a single operational amplifiers are also available, but do not achieve the low drift and low bias currents of more advanced devices. Device specifications for instrumentation amplifiers include the number of analog channels and the number of differential channels. When single-ended outputs are available, suppliers often specify the maximum number of analog channel outputs as twice the number of differential outputs. Differential channels, which have two inputs, define the voltage as the signal to process between the two inputs. Other device specifications for instrumentation amplifiers include maximum output voltage, gain range, and input impedance. Gain, the factor by which input signals are multiplied, is frequently greater than unity; however, gain can be fractional when a reduction (attenuation) of signal amplitude is desired. Impedance, the resistance to alternating signal flow, is a result of the resistance, capacitance, and inductance of a device’s circuitry. For instrumentation amplifiers, input impedance is typically specified as much greater than the impedance of the devices whose signals are amplified. Additional specifications for instrumentation amplifiers include AC and DC voltage inputs and integral filters that allow some signals to pass while blocking others. Instrumentation amplifiers also vary in terms of common mode rejection ratio, a measurement that is expressed mathematically as CMRR = 20 log (differential gain / common mode range). An amplifier’s ability to obtain the difference between two inputs while rejecting the signal common to both is defined by both the CMRR and the common mode range. Instrumentation amplifiers are available in a variety of form factors. Some devices mount on integrated circuits (ICs), standard DIN rails, or printed circuit boards (PCBs) that attach to enclosures or plug into computer backplanes. Others bolt into walls, cabinets, enclosures, or panels. Rack-mounted units fit inside a standard 19” telecommunications rack. Modular styles include stackable units that dock in bays, slots, or boxes. Benchtop or freestanding instrumentation amplifiers often feature full casings or cabinets and integral interfaces.
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Circuit designers often encounter the adverse effects of common-mode noise on a design. Once a common-mode problem is identified, there are several ways that it can be resolved. However, common-mode...
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The common-mode rejection ratio (CMRR) of a differential amplifier (or other device) measures the ability of an amplifier to obtain the difference between two inputs while rejecting the signal. A high...
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Engineering Web: Instrumentation Amplifiers
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Analog Devices: Instrumentation Amplifiers: Design Center: Design Handbooks
Chapter II - Inside an Instrumentation Amplifier (pdf, 267,016 bytes). . * Chapter III - Monolithic Instrumentation Amplifiers (pdf, 971,517 bytes). . * Chapter IV - Monolithic Difference Amplifiers ...
See Analog Devices, Inc. Information
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Analog Devices: Instrumentation Amplifiers: Design Center: Application Notes
AN-245: Instrumentation Amplifiers Solve Unusual Design Problems (pdf, 556,888 bytes). Traditionally Considered Only for Transducer-Conditioning Applications, Instrumentation Amplifiers Bring Unique ...
See Analog Devices, Inc. Information
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New Designer's Guide to Instrumentation Amplifiers
New Designer's Guide to Instrumentation Amplifiers This 126-page guide helps engineers select, evaluate, and design the most appropriate in-amps for specific applications by covering a wide range of ...
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Sensors - Home Page
By using an indirect current-feedback topology, instrumentation amplifiers can avoid some of the pitfalls inherent in using three op amp instrumentation amplifiers powered from single supply voltages.. ...
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Linear Technology - Instrumentation Amplifiers
... Single Resistor Sets the Gain of the Best Instrumentation Amplifier. *DN302 - Ultraprecise Instrumentation Amplifier Makes Robust Thermocouple Interface. *DN323 New Instrumentation Amplifiers Maximize ...
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Part Numbers for Instrumentation Amplifiers
| Part # |
Distributor |
Manufacturer |
Product Category |
Description |
| 52301 |
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Micropac Industries, Inc.
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Instrumentation Amplifiers
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Low offset voltage, nonlinearity and noise, high CMR and input impedance |
| Model DLD-CH |
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Honeywell Sensotec
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Instrumentation Amplifiers
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Amplifier for AC LVDT's, 4 to 20 mA output |
| Model PR 710 |
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Wilcoxon Research
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Instrumentation Amplifiers
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Powers 700 series accelerometers, low noise amplifier for each channel |
| Model 4601 |
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Columbia Research Labs, Inc.
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Instrumentation Amplifiers
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Low cost charge amplifier, wide bandwidth, low noise, low output offset |
| Model 2680M14 |
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Endevco Corporation
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Instrumentation Amplifiers
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Single channel, for use with piezoelectric transducers, small & lightweight |
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