ADAU1761

Hello vag,

This question might be better asked of our linear group. I thought I recognized this part but I looked it up and I think I am wrong. However, I do not think this is an ADI part.

Many of these parts require the source impedance of the reference to be a very low impedance. The CM pin will not be a low impedance. I am not certain exactly what the output impedance is for this part but with several of our other parts it is around 5k ohms. So you will have to use a buffer on the CM pin. Just a voltage follower would suffice. You would still need the filter caps on the CM pin.

So yes, your original question about removing the coupling cap is correct. At this point the voltage will sit at the VREF voltage when there is no signal.

Dave T

Hi DaveThib,
Thank you very much for your answer.
It is a general picture of an instrumentational amplifier. Yes, I will add a voltage follower between the CM pin and the VREF pin of the instrumentational amplifier.

Therefore, should the circuit works correctly? Obviously by adding the buffer in series with the CM pin.

Thank you again for your time and help.

Hello vag,

I think it will work correctly but it is something I have never tried personally. There may be a detail I missed so please let us know how it works and if there were any surprises.

Dave T

Hi Dave,
Thank you very much for your time and help.
After the test I will report the results!

Doesn't works, in addition this connection damages the internal Vdd/2 bias circuit...
Because if there are a DC component different from 0, this force the input pin an a different voltages respect to the Vdd/2.

Hello Vag,

The internal common mode voltage generator has a high impedance to the CM pin. So if you are drawing any current from the CM pin it will sag but it will not damage the internal generator.

If your external circuit is pulling too much current from the reference then you can buffer the CM pin with a voltage follower that can supply more current.

Dave T