Electronics > Projects, Designs, and Technical Stuff

Instrumentation Amplifier Modification or Replacement

**loop123**:

I'd like to change the AMP01 instrumentation amplifier to the top one with best spec ever. First some technical discussions. This is its datasheet and its spectral density graph.

https://www.analog.com/media/en/technical-documentation/data-sheets/amp01.pdf

I know that to convert to Voltage in RMS. Multiply nV/Sqrt(Hz) to the square root of the bandwidth.

Let's use 100Hz bandwidth as example (actual example).

from the graph with spectral density 5 nV/Sqrt (Hz). V(rms) = 5nV/Sqrt (Hz) multiply by Sqrt (100) = 5nV * 10 = 0.000000005 x 10 = 0.000000050 V or 50nV.

So the noise is like V(rms) = 50nV.

In my application. I need to run it at 10uV (microVolt) input using 1000Hz-3000Hz frequency with good noise profile.

What instrumentation amplifier to replace the AMP01 that is the top or the best out there that can use 10uV input with 1000Hz-3000Hz frequency with not visible or minimal noise?

If possible. The frequency can be 10,000 Hz instead of 1000Hz. Just give the instrumentation amplifier with the highest bandwidth that can do it.

Thank you.

**moffy**:

In such an application, shielding, both thermal and electrical is very important. I found a ground plane top and bottom as well as a shielded box for both electrical and thermal effects is essential. You also need to determine if your PSU is inducing the noise, use a battery supply as a reference to check the difference.

**loop123**:

Ok.

Say. If two instrumentation amplifiers have same nV/sqrt (Hz) lets say 5 nV/Sqrt (Hz). It means they have similar noise at say 1000Hz or 2000Hz bandwidth?

Know the top Instru Amps (INA) model out there that accept differential signal with 1uV to 10uV 1000Hz-2000Hz with very clean output with noises in the nV instead of uV? What is the lowest spectral density figure available? like is there a 1nV/sqrt (Hz) or even 0.5nV/sqrt (Hz) Instru amps?

**moffy**:

--- Quote from: loop123 on February 15, 2024, 10:28:45 am ---Ok.

Say. If two instrumentation amplifiers have same nV/sqrt (Hz) lets say 5 nV/Sqrt (Hz). It means they have similar noise at say 1000Hz or 2000Hz bandwidth?

Know the top Instru Amps (INA) model out there that accept differential signal with 1uV to 10uV 1000Hz-2000Hz with very clean output with noises in the nV instead of uV? What is the lowest spectral density figure available? like is there a 1nV/sqrt (Hz) or even 0.5nV/sqrt (Hz) Instru amps?

--- End quote ---

Depends on the input impedance of the circuit. The THAT1512 can have 1nV/hz^0.5 but that is with zero input impedance and 60dB of gain, but current noise can easily become the dominant factor at around 1k ohm perhaps lower, in which case a JFET input amp is a better choice. What you are seeing though is induced pickup and you won't even get close to the performance of a good instrument amp if you don't pay serious detailed attention to what was mentioned previously, both electrical and thermal shielding as well as power supply noise. You should also aim for a true differential input to try and maximise CMRR.

**loop123**:

No problem with power supplies as I used batteries only. The circuit has metal cover on all corners and I may use Faraday cage (know where to get these to enclose projects?) About thermal shielding. Did you mean putting it in very cold aircon? How to do thermal shielding?

It is true differential input with about 10kOhm source impedance. So what state of the art INA (Instrumentation Amp) that can accept high input impedance, etc. It should be something that is significantly better than the AMP01. Actually it will be used as EEG with microVolt input but with 1000Hz frequency so I can lessen the gain when time to switch to milliVolt EMG and still have the 1000Hz-2000Hz capability. I already have the finished product but it uses AMP01 so for my project. I'll replace the amps to the best one in the world. I have 2 units. One is for experiment. Don't worry about Galvanic isolation because it is all purely powered by 1.2V rechargeable Eneloop batteries.

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