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.

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Potentiostat calibration and measurement

Maybe this question is obvious, but I'll try. I am trying replicate this potentiostat without R5: In the interests of calibrating it I've joined the reference and the counter electrode to resistor of ...
1 vote
2 answers
41 views

PGA207 Feedback Issue Modification

I have mistakenly used an instrumentation op-amp (PGA207) in the place of a normal op-amp in my design, so now I have to make adjustments to my circuit. A snippet of the datasheet from the op-amp I ...
6 votes
2 answers
221 views

PGA207 op-amp gain issue

I have an issue with the PGA207 instrumentation op-amp. I connected it as a voltage buffer, as seen in the following image: When I connect a 1 kHz, 2Vpp sine wave to the non-inverting input (pin 5) ...
1 vote
1 answer
364 views

Why aren't these instrumentation amps working for linearly driving a generic MOSFET?

If you've read my previous posts, I would say now that I've pretty much given up on the idea of parallelizing op-amps. I've stumbled onto instrumentation op-amps and decided they were good enough for ...
0 votes
1 answer
27 views

Instrumentation Amplifier Simulation INA122P Output Voltage not zero (TINA-TI)

I have the following circuit, the INA122 instrumental amplifier. when RG pins are not connected, the default gain is 5. I am sure that the bridge is balanced, however, for the simulations, why there ...
2 votes
1 answer
94 views

Question on INA122P non-linear gain

I am trying to apply gain for a 0.0 - 16.7 mV signal with an INA122P, with a single 10 V supply for all the circuits, with Vref driven at 0.0 mV. Here is the circuit that I am using, no Rg applied, ...
5 votes
1 answer
76 views

Instrumentation amplifier cross-connection circuit

I am trying to implement a circuit from an ADI app note that I have not seen anywhere else : Here it is in PDF format which is a copy of this article. I strongly encourage reading it as it is quite ...
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3 votes
3 answers
139 views

Instrumentation amplifier noise considerations

I am trying to understand and calculate the expected noise behind a simple NTC-bridge circuit where the signal is amplified by a instrumentation amplifier. My goal is to measure 1 mK temperature ...
2 votes
2 answers
345 views

Oscillating instrumentation amplifier with transformer coupled input

I want to amplify an output signal from a sensor. The sensor is made of three inductors which are coupled. One primary inductor with 25uH and two secondary inductors wired in the opposite direction ...
3 votes
1 answer
92 views

How to eliminate the noise of this circuit?

I've built the following circuit on a PCB with reference to a TI's solution. I changed the gain of the INA to 10 and the gain of the A3 stage to 40. I also changed the cut-off frequency of the A4 ...
-1 votes
1 answer
55 views

AC and DC-coupled amplifiers in parallel

I am curious of the effects of a circuit setup like this, with a AC-coupled (capacitors before inputs) and a DC-coupled (no capacitors) amplifier measuring a potential difference in parallel. ...
1 vote
1 answer
45 views

What is the reference voltage of Vin- and Vin+ in this circuit?

I'm trying to make a PCB board to measure Electrocardiogram (ECG) signal. I have some doubts about the DC offset of the 2 input signals (\$V_{IN-}\$, \$V_{IN+}\$) with reference to analog ground. I ...
3 votes
1 answer
78 views

Instrumentation opamp saturating

I'm building a circuit to measure signal out of a wheatstone bridge for strain gauge. here is the schematic: simulate this circuit – Schematic created using CircuitLab I applied +-1.5V with ...
0 votes
1 answer
55 views

Questions on Vss for op-amps (differential amplifier)

I was working on a voltage amplifier and confronted the following problem regarding Vss of the op-amps. The op-amps I am using are MCP603T-I/Ps. The circuit diagram is as shown below. (INSTRUMENTATION ...
3 votes
5 answers
413 views

Instrumentation amp giving only positive output (with + and - power supplies)

I'm using an instrumentation amp for a bridge circuit for strain gauges. However, the output range is always positive (the lowest value I can get is zero). The amp I use is AD620. For power supply I ...
1 vote
5 answers
140 views

Potential problems when using a high resistance voltage-divider

I want to design a circuit, that allows me to measure the voltage across a piezoelectric transducer. The transducer itself has an impedance |Z| of 500 Ohms up to ~20 kOhms. The voltage to measure ...
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4 votes
2 answers
240 views

In-Amp Common Mode Rejection With Unbalanced Device Impedance

I am using an instrumentation amplifier (AD8220) to interface a pH probe. The pH probe produces a +/-414mV signal with large output impedance (>100MOhm). AD8220 has very low input bias current (~...
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0 votes
1 answer
34 views

Overall CMRR of analog front-end

My analog front end input consists of a chain of (instrumentation amplifier + differential amplifier + and ADC). Is the CMRR of the overall chain only considered based on the first element that is ...
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2 votes
1 answer
135 views

Which variant of amplifier to use?

I am making a pressure sensor circuit according to page ten of the manual here. There are just too many types of the recommended sensor LMV324 available in the SOIC type. Can someone help me decide ...
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1 vote
1 answer
72 views

Is it possible to connect a Vin to a ref of an instrumentation amplifier?

I have a circuit in which I need an instrumentation amplifier (INA128 (datasheet)) to be connected correctly for it to work. I don't know if it needs another resistance or if the input needs to be ...
0 votes
1 answer
111 views

Need help to understand this circuit

I'm trying to understand this circuit, it's been a long time since I messed with electronics. I even managed to understand some things, for example: The first ICL7660 circuit will be used as a source ...
-1 votes
2 answers
102 views

Why are there so many variants of an Op Amp? Which one to chose? [closed]

I am directed in a user manual (Page 10) to use the LMV324 Amplifier. But when I search on the net there are just too many types of this amplifier with a lot of different types of suffixes. I need to ...
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1 vote
3 answers
429 views

Failed to find DC operating point for AC analysis LTspice

I finally successfully added the MCP 606 (MCP 609) in LTspiceXVII. I am now facing an error "Failed to find DC operating point for AC analysis". I have checked the maximum supply of MCP 606 ...
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0 votes
1 answer
177 views

How do I connect a female EEG electrode to a breadboard?

Electrode output end: EEG electrode: I'm trying to connect the output of EEG electrodes to a breadboard as input. How do I connect the electrode to the breadboard? Usual jumper wires don't seem to ...
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2 votes
1 answer
52 views

I want to start by doing a circuit analysis of the triferential subtractor

I want to understand the circuit of the triferential subtractor: in the context of Anderson loop based signal conditioning, found in this resource here. This is just an inverting amplifier with a ...
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2 votes
2 answers
157 views

What would be the amplification circuit for PP02 sensor using LM324 pressure sensor?

I am planning to use the PP02 Omron pressure sensor. The user manual of the sensor (Usermanual link) suggests using LMV324 type of instrumentational amplifier with four op amps within in the schematic ...
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110 views

Oscilloscope "isolated" inputs

As I don't want to see my oscilloscope go up in flames when I play with probing circuits, I was wondering the following: First off, my goal is to measure different floating voltages aka the "GND&...
-1 votes
1 answer
57 views

Options for current sensing for a 230V , 100 W boost PFC circuit?

So I have the following boost PFC circuit: I wish to sense the inductor current. My first thought was using shunt with instrumentation amplifiers, but the issue is total voltage across the inductor ...
1 vote
1 answer
252 views

INA128 - what is wrong with this circuit?

I built a circuit based on the INA128 which for some reason heats up rapidly. The test setup is like the image below. The output is left unconnected, no input signal. I get around 550mV voltage drop ...
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3 votes
2 answers
159 views

Is there an affordable way to balance a bridge without using expensive resistors?

I have a full and balanced bridge circuit with four through-hole \$ 350 \,\Omega \$ resistors and an instrumentation amplifier AD8293G80 that has a gain of 80. Both the bridge and the amplifier are ...
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0 votes
3 answers
86 views

How to make sensor input look like high impedance on loss of 5V power?

I have a strain gauge sensor with a full-scale output of about 8mV and an output impedance of 5K ohms. We will be measuring its value with a max sample rate of 500Hz, and 10 bits of resolution. It ...
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2 votes
1 answer
139 views

BMS Two Stage OP Amp

My company is designing a 4 cell BMS. We recently did a redesign of our cell voltage measurement circuits and are having major issues. The first stage of each amplifier is a differential opamp with ...
2 votes
2 answers
296 views

Trouble simulating an instrumentation amplifier on KiCad

So... I'm trying to build an EMG sensor for biofeedback purposes, but I'm having loads of trouble both on the breadboard and on the CAD side as well. I'm using a M1-processor mac mini which could be a ...
0 votes
2 answers
73 views

Amplifier detector circuit simulation

I wanted to do falstad.com simulation of the circuit(link to schematic): Falstad isn't familiar to me, so I'll be grateful for showing me how it should be drawn. I think detector could be replaced by ...
-1 votes
1 answer
131 views

Output Voltage of Instrumentation Amplifier Configuration

I'm trying to find the output voltage using the superposition theorem for this circuit configuration when RG is connected. I'm working with ideal op amps. As far as I understand the circuit, when VB ...
0 votes
1 answer
64 views

Instrumentation amplifier AD8293G160 - Why RC filter calculations don't match?

I am using an AD8293G160 to handle a signal, for a known bandwidth. The part is an INA with a fixed internal gain of 160x. It has 2 outputs, one direct, the other with an integrated 5k resistor to ...
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13 votes
4 answers
1k views

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 ...
-1 votes
1 answer
40 views

Is one RLD electrode enough for multichannel ECG acquisition system?

I am trying to design the multichannel ECG measuring device. My device has to acquire 3 signals at the same time. I have to use 6 electrodes to be able to measure those signals. My problem is each ...
0 votes
2 answers
110 views

Why is the output of this instrumentation amplifier not constant?

So here's the circuit and output voltage, the model is AD620: So according to theory (Vout = 49400/49400 +1)*(2-1) ) i should obtain 2V as the output voltage. Well what i got in LTSpice was a value ...
1 vote
1 answer
65 views

Does CT act as a constant current source for a specific primary current?

I connected several resistors (1, 10, 100, 560 Ω) at the output of a 1000:1 CT (0-100 A measurement). I saw that the secondary current doesn't change for different resistors for a constant primary ...
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-1 votes
2 answers
124 views

What are the advantages of an instrumentation amplifier over a single op amp amplifier? [closed]

Basically, strain gauges are going to be connected to a Wheatstone bridge and the output from the bridge will be amplified by an instrumentation amplifier. But what are the advantages of this over a ...
0 votes
0 answers
79 views

Instrumentation amplifier for high impedance on both inputs, why it is beneficial

Instrumentation amplifier is a differential amplifier with two voltage followers before it. This solves the issue with that an op amp differential amplifier will provide a low impedance path through ...
5 votes
2 answers
2k views

How does a driven right leg work?

A driven right leg (DRL) circuit is often added to a biopotential amplifier to reduce the common mode voltage (i.e. to increase the common mode rejection ratio, CMRR). A basic form of biopotential ...
0 votes
1 answer
64 views

Why does gain of my INA2332 change with increase in input voltage?

I'm building an IoT circuit for sensing resistance change using Kelvin's 4 wire. I have implemented a constant current source that supplies my two sensors connected in series with 50 mA. The output ...
6 votes
2 answers
761 views

Why is the instrumentation amp distorting the signal on the input?

Here's my schematic. A current source is driving a resistive sensor. The sine wave is to mimic the behavior of the current real supply and doesn't play a role in the distortion. It's approximately ...
0 votes
0 answers
59 views

How do you measure the differential gain in an instrumentation amplfier?

How can I measure the differential gain Ad from the formula s = Ad(e1-e2) in the following circuit?
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-4 votes
1 answer
73 views

AD8421 output AC or DC? [closed]

Is the output of the AD8421 AC or DC?
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1 vote
2 answers
83 views

Current Sense Amplifier / Differential Amplifier Negative Voltage On GND pin OK?

Right now I'm picking a current sense amplifier for my application, and I'm looking for for amplifiers with maximum offset voltage of below 50uV (and offset and bias currents in nA/pA range). Luckily, ...
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1 vote
1 answer
141 views

Why does the input of the op-amp introduce a DC offset to my signal?

I'm interested in measuring the resistance change in a sensor (pk-pk about 1ohm) using an instrumentation amplifier. I chose to go with a constant current source to get the best possible sensitivity ...
3 votes
1 answer
146 views

Digitally tunable gain, low-noise instrumentation amplifier

I want to make a digitally-tunable gain (~1 to 1000x), low-noise instrumentation amplifier. There are integrated ones (e.g. AD8557) but the input noise is too high. My current plan is to use an ultra-...
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