Help with impedance matching

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lizbeth0188

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I connected 16 instrumentation amplifiers for a EEG amplifier design.I have shorted all the reference and all amplifier have a common reference.But while doing this I find that the noise picked up by the amplifier has increased.One possible reason for this is since I have shorted all the reference together ,the impedance in the reference input is dropping.As a result the CMRR of the amplifier is unable to provide suitable attenuation for the common noise signals.Is there any way to match the impedance between the reference input and active input in the all instrumentation amplifiers?Is there any other solution you could provide for this issue?Tried providing a unity gain op-amp circuit to the reference input.But didn't help much.
 

If the amplifiers became more sensitive to the pickup noise, consider a better screening and input low´-pass filtering.
 

For the EEG frequency spectrum, you will need to know the source impedance to be matched. To my knowledge, EEG amplifiers have a high input impedance, no care to match to the source.
 

 

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