Electrical Engineering Stack Exchange
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Questions tagged [instrumentation-amplifier]

An instrumentation amplifier (InAmp) is an integrated circuit or operational amplifier topology that has high input impedance differential inputs and a low impedance single-sided output. Because of precision laser-trimming techniques for passive circuit elements, InAmps implemented as integrated circuits can achieve impressive common mode rejection ratios, while discrete OpAmp implementations can be disappointing in this regard.

Recommended reading

A Designer's Guide to Instrumentation Amplifiers, written at Analog Devices Inc. by Charles Kitchin and Lew Counts, gives a comprehensive overview of Instrumentation Amplifier technology and application. This classic text is available free of charge.

Three-OpAmp Instrumentation Amplifiers: Advantages & Disadvantages

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When is it an instrumentation amplifier (In-Amp) and not an operational amplifier (Op-Amp)?

I've seen a number of different configurations for instrumentation amplifiers, including 2 opamp versions. This is also one. But it's just a differential amplifier preceded by input buffers. When do you call it an instrumentation amplifier, in…
Federico Russo
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Op-amp input resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is an instrumentation amplifier that apparently uses an inverting amplifier's output instead of a ground in the lower-right corner of the above figure, but…
In silico
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Why would I want to use a differential op amp configuration while amplifying differential signals?

A basic instrumentation amplifier looks something like this: My understanding is that you can feed this circuit with a differential signal while not loading the signal too heavily because of the high input impedance of the op-amp buffers. But why…
Slovak Rocketry
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Why is my instrumentation amplifier's gain non-linear?

I am using an AD8226 instrumentation amplifier as the pre-amp in a circuit which uses a micro fuel cell oxygen sensor to measure oxygen content in a gas stream. The pre-amp is configured in single ended supply mode, with a 5 V supply. Gain…
Matt B
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Why are two stages used for an instrumentation amplifier?

When we have a two-stage instrumentation amplifier, such as the following. Why do we need the first stage of the two Operational Amplifiers? Couldn't we just input V1 and V2 into the differential amplifier?
Bee
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How to avoid Johnson noise in high input impedance amplifier

I don't have a circuit I'm working on, this is more of a theoretical question - I am trying to remedy a flaw in my understanding. Imagine I want to build a high input impedance amplifier to work in the low mV range, with a few nV/√Hz noise. I want…
Jack B
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Active guard shielding for instrumentation amplifier

I want to use the the AD8221 amplifier as a conditioner for my load cell. I saw that to reduce noise I can use an "active guard shield driver" between the "REF" of my amplifier and the shield. If someone has already worked with something similar…
user278935
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Why include a small resistance between op-amp stages

I have been reading through TI's reference material on constructing a current source. http://www.ti.com/lit/an/sboa046/sboa046.pdf In figure 52 there is a 150ohm resistor included between the output of the instrumentation amplifier and the input of…
Hugoagogo
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Mysterious Op Amp noise

I have a very good op amp (AD8551) that I use to dynamically amplify a very small signal (2x, 10x, 100x, 1000x gain). The problem is that there is a noticeable noise level at 100x and 1000x gain, and it has a weird constant shape. If I power the…
Chris
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Do you have to use an instrumentation amplifier to measure voltage across a 0.01 ohm shunt?

I was planning on implementing a current sense feature on the STM32 Bluepill to measure the current output of a solar panel (150 mA short-circuit current, 14 V Open-circuit voltage) using LM358 single-supply op amps and a 0.01 ohm shunt. No matter…
A.H.Z
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Understanding the guarding circuit in an instrumentation amplifier

I've got a project to make but I have trouble understanding what is actually going on. In circuit below, I have to calculate the resistor values, choose op-amps and explain how the whole thing works. This is an in-amp for EMG and I can't understand…
Archimedes
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What does common mode voltage stand for in an instrumentation amplifier?

I was reading a text about instrumentation amplifiers. I couldn't find any easy explanation what really common mode voltage means and its importance.
user16307
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Circuit for small level voltage detection (microvolts)

I have been working on a project lately which help in the detection myogenic potentials (of the levels of micro-volts). After studying from several places, I finalized the following test circuit. The initial voltage dividers helps in generating the…
DodZi
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RC Lowpass Filter between Amplifier and ADC input

I have sensors (pyranometers that consist of thermopiles and measure sun irradiation) that ouput a low voltage signal so I need to amplify them using an instrumentation amplifier. I have chosen the AD8237 for this task: Datasheet I'm using a gain…
H123321
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Instrumentation Amplifier - how to use it correctly

I am trying to perform some measurements based on a special technique used to detect corrosion in rebars of concrete bloc. The idea is to measure the potential difference between an electrode and the rebar: I tried it with a conventional voltmeter.…
Pelotudo
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