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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.

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Signal response and settling time graph analysis

I have come across a datasheet of an instrumentation amplifier. I have a difficulty in understanding the signal response vs settling time graphs. Can someone please explain figure 28(page 10) of the ...
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Instrumentation Amplifier - is it possible to have an output signal inverted, with respect to the supply voltage?

I'm doing some circuit design in order to translate a load cell input into the pedal input of a Logitech G27. What I want to achieve involves having a balanced state output as close to 5V from the ...
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436 views

How to make repeatable Op-amp amplifier circuit

I did a simple op-amp based 100X gain single ended circuit. I tried to order 100 IC's and manufactured them. But found that out of 100 only 60 devices have same and expected baseline. What could be ...
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102 views

Amplifier with true ground output swing and A/D conversion

I want to amplify a 0-20mV signal from a sensor to 0-2.048V in order to feed it to an ADC (with a reference voltage of 2.048V). After I will input the digital signal to a microcontroller. I need to be ...
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681 views

What is the purpose of op-amp in the output of Instrumentation amplifier

I encountered a problem while solving an analog circuit. I just need to know the purpose of the last op-amp (K4) at this circuit: while solving I understand it just amplify the output voltage from ...
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Mathematical model for differential signals and relation with reality

i have a question and i hope is not that strange. i spend some time asking myself how people came out with the mathematical model for differential signals and why is this better in this way?! to be ...
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77 views

How do I keep this VCCS stable?

I have designed a circuit to measure impedance of certain tissues. It injects a constant current from two electrodes and measures the voltage at different electrodes. The system mainly consists of a ...
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48 views

Effect of changing current sense resistor value in amplifier circuit

I am trying to implement a current output amplifier circuit shown below. Current is measured across sense resistor Rs to adjust input voltage Vin. Gain: G = -Iout/Vin = R2/(Gain-of-IA1*R1*RS) The ...
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Building circuit to amplify small sensor signals using an Instrumentation Amplifier and 24-Bit ADC

I'm a beginner when it comes to circuit design and I have spent the last few weeks doing research on this topic. I have now chosen some ICs (Instrumentation Amplifier and ADC) and would like to build ...
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Instrumentation Amplifier Output Voltage Questions

Ok, so I am currently trying to build a temperature sensor based Instrumentation Amplifier circuit using the AD8429 (data sheet link here). The schematic for my circuit so far is below: A very basic ...
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35 views

Calculating drift/precision on a temperature circuit

I'm hoping to get some guidance with a circuit I designed. I have a current source which operates between 200uA and 400uA. In order to measure it, I used the following circuit before feeding it into ...
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77 views

ECG electric design: 1 and 3 op-amp designs from a safety point of view

During the design of an ECG using an instrumentation and a differential amplifier, we can across this question: Comparing the one and three op-amp designs from a safety point of view: of the two ...
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Improve a ECG I am using an instrumentation amplifier

I am doing an EMG as a part of my senior design project. I am currently using an Instrumentation amplifier but my professor suggested using a driven right-leg circuit. I was wondering how using a ...
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692 views

How to determine op-amp gain with active feedback?

The Howland current pump uses an op-amp in the configuration below with a resistive feedback network which gives me the gain show below: But if I decide to swap the feedback resistor for an ...
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58 views

Measurement of high voltage with low voltage circuit

Is it possible to make a high-impedance, precision measurement of a 10V DC signal (dynamic range requirement is only ±1V with a DC-1kHz BW) using amplifiers and an Sigma-Delta ADC supplied only by +3....
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70 views

How does common mode range include the negative rail?

How do the devices like AD8220 handle the common mode voltage equal to the negative rail or even lower voltage (Take a look at figure 30 of AD8220 datasheet) ? Does the operation of the amplifier ...
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145 views

Is there any difference between AD620 vs INA128?

I'm trying to make an EMG sensor. I've found some tutorials, for example, DIY muscle sensor/EMG circuit for a microcontroller, but my main question is can I make an EMG sensor using AD620 instead of ...
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Spice model for analog devices instrumentation amplifier giving unexpected outputs

I'm trying to do noise analysis with the AD8421 (although the specific in-amp doesn't matter). Right now I have two time dependent voltage sources on the inputs of the amplifier and the output seems ...
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Why do tube amplifiers have such (relatively) small reservior capacitors?

In learning about guitar amps, I've been studying the schematics for solid state and tube amplifiers, and I found a pattern that I've never seen an explanation for. If you consider any of the main ...
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Instrumentation amplifier for current transformer

I am using a current transformer to make a power meter to measure the electricity usage of a flat With a gain of 50, and a reference voltage of 2.5V, the amplifier should map the ±50mA:1Ohm=±50mV to ...
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131 views

AD620 instrumentation amplifier with Wheatstone Bridge-based KMZ10B sensor

I would like to ask for help regarding a certain phenomenon related to amplification by the Analog Devices AD620 instrumentation amplifier (device home page, device datasheet). Vcc is 5V. The AD620 ...
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26 views

Diifference between INA827AIDGK & INA827AIDGKR

Whats the difference between the same package of the IC INA827 - INA827AIDGK vs INA827AIDGKR? The datasheet makes no mention of any differences. Except in in.element14.com where INA827AIDGK is ...
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Howland vs instrumentation amp VCCS

I found an article on the Analog Devices site going over some different Voltage Controlled Current Source (VCCS) designs and I noticed an interesting one that used an Instrumentation amplifier along ...
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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 ...
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156 views

Instrumentation amplifier output stuck high

I tried to design an inamp for a K-type thermocouple. In theory the gain of this amp should be 250 (close enough to 10 mV/K), and if my understanding of instrumentation amplifiers is correct the ...
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2answers
144 views

Why does an Instrumentation Amplifier need a reference?

I am working with the INA826EVM board and I am wondering why it needs an additional op-amp for a reference in the Instrumentation Amplifier?
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126 views

Why CMRR degrades in Instrumenation Amplifier?

Why CMRR degrades in Instrumentation Amplifier when R3 (only the feedback resistor) is increased keeping all other resistances constant at a fixed value? What mathematical relationship links R3 and ...
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3answers
124 views

Create small variations in voltage for opamp reference pin

Hello and thanks beforehand. I'm designing a circuit to measure 4 wheatstone bridges using 4 Analog Devices AD8422 in-amps. Now, i'm feeding the AD8422 output to a 3.3V ADC, so i'm offsetting the ...
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152 views

LTspice simulation of AD8421 instrumentation amplifier giving incorrect output voltages

I am trying to run a simple simulation of an instrumentation amplifier (AD8421, model from here) running on a single supply, but the output does not seem to be correct. The screenshot below shows the ...
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Maximum Gain For Chopper Stabilized Instrumentation Amp (MCP6N11)

I am using a Microchip MCP6N11 chopper stabilized instrumentation amplifier to amplify the signal from a MPX2300DT1 Wheatstone bridge pressure sensor. My schematic is attached. As shown the gain is ...
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2answers
84 views

Noisy amplification and low light: photodiode and op-amps question

My formal education was in mechanical engineering and I’m well trained in some CS as well. Yet here I am on an electrical project (that will eventually turn CS). I have been lost and confused for many ...
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2answers
194 views

Art of Electronics figure 5.87 (revised)

The circuit below comes from the errata of The Art of Electronics. Why is the circuit in Figure 5.87-B (bottom) correct? As drawn, 50 mA at output will mean -5V at the inverting input of the Op-Amp. ...
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203 views

high input impedance circuits

Working with circuits to get high input impedance. This is to capture signals while introducing as little interference as possible to the preexisting circuit, to load the source as little as possible. ...
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152 views

Instrumentation Amplifier input saturation problem

I designed and ordered some PCBs for in-amp but having a problem, I think it is input saturation. The power supply is 0V, 6V, and 12V rather than -6V, 0V, 6V but I am only interested in AC so this is ...
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109 views

Effects of increasing current on external noise and SNR for analog transmission

This is a conceptual question about long analog signal transmission exposed to capacitive coupling and EMI noise as shown in below figures: simulate this circuit – Schematic created using ...
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125 views

Using Ins Amp as current monitor

I am using a ready board (using AD620) in my circuit as a current monitor.I have set the gain of the board to 10x. 1)My first question,is this a right way to approach the problem.My trials show that ...
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How to outline the signal path of this schematic?

I'm looking for some help finding out the signal path from input to output when the effect/normal switch on the far right is on normal. I couldn't figure out which path the signal takes when the ...
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68 views

circuit for mesure positive & negative voltage + Vref resolution

i would like to make a "voltmeter" to read from +2V to -2V and connect it to an Arduino ADC ( 0V to 5V ). I found different configurations for do this job: From this site: Bipolar to unipolar ...
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1answer
54 views

Power amplifier measurment

How are amplifier output power ratings measured? Can I measure the output power with a watt-meter or oscilloscope directly? Can I measure the output impedance and then apply a Kirchhoff law? I have ...
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1answer
160 views

Building a VCCS with AD8220 Instrumentation Amplifier

This question is to help me with my work in building a VCCS for the excitation signal of an Electrical Impedance Tomography measurement set-up to use with EIDORS. I have only basic knowledge in ...
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1answer
42 views

Understanding Impedence when modifying a spring reverb

So I found this spring reverb tank on Amazon for $17. I understanding that it is supposed to be used inside a guitar amp but I want to see if I can modify it to be a low-cost spring reverb for use ...
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1answer
146 views

Two Op-Amp Instrumentation Amplifier - Gain derivation

I came across the following appnote(slyt647) which analyses the two op-amp instrumentation amplifier topology. The gain was found by finding individual gains for each op-amp and adding them in ...
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what is the maximum load for an instrumentation amplifier, in particular the AD620?

From the reading of This datasheet, I can't figure out what is the maximum load I can put at the output. To make my question more precise, suppose I need a gain of 10 (for DC measurements), for an ...
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2answers
104 views

Avoid in-amp common mode and ADC input protection

I'm designing a temperature measuring circuit using a PT100 on a wheatstone bridge. In the temperature range I'm measuring (0-45C) I should get 0-25.5mV from the bridge and then amplify the signal to ...
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1answer
64 views

Load cell amplifier inverse voltage output

I'm making a load cell modification to my Logitech G29 brake pedal. The potentiometer on the existing pedal have inverse voltage so 5V is no brake applied and 0V is max brake applied. This is inverse ...
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1answer
58 views

Tape archival data acquisition

I have some old tapes (the compact cassette variant) and an old Technics deck. I want to digitally archive these tapes as best as I can. The original deck is from the late 80s and contains a standard ...
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2answers
110 views

Can Texas Instrument's INA332 really be used for EEG?

On TI's datasheet, it specifically lists EEG as one of INA332's potential uses. EEGs are microvolt level signals, and the INA332 has input offsets of +/- 2 milliVolts. 73db CMRR is quite low, but ...
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Bang-for-buck in purchasing an instrumentation amplifier for three-electrode EEG recording?

While my forte has been in digital signal processing for most of my life, not-so-recently I've made the mistake of venturing into analog signal processing for a well-endowed client. I've primarily ...
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Purpose of these resistors in the input of in-amp

there is an instrumentation-amp here. there is two electrodes which in primary sensor get uv to a few mv ac induced voltage. and also impedance of the primary sensor is too high and as i know reason ...
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Instrumentation amplifier with capacitor in the feedback network of the first stage

Instrumentation amplifier with capacitor in the feedback of the first stage. Is this a second order filter or should be analyzed as just first order filter parallel coupled at Rg. Av = 1+2Zf/zg z2= ...