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I have AC signal that varies from 50mV (pk-pk) to 420mV (pk-pk). I am trying to use a PGA (programmable gain amplifier) to amplifiy the signal so that it can be sent to the ADC in an ATmega328P. The signal sent to the ADC needs to be within 0-3.3V. I can't add a DC shift centred around 1.65V before passing it through the PGA, as this will also amplify the DC shift, which puts the signal outside the ADC range. How can I go about shifting the signal and amplifiying it using a PGA which is supplied from a single supply?

tamilnewzealand
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    I guess that your PGA didn't come with a datasheet or model number, otherwise you would surely have mentioned such an important detail. – pipe Sep 07 '16 at 05:13
  • I didn't include the PGA model number as the model I will use has not been decided yet. I was considering the MCP6S91. – tamilnewzealand Sep 07 '16 at 07:50

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I can't add a DC shift centred around 1.65V before passing it through the PGA, as this will also amplify the DC shift

Yes you can, and you have to. The PGA you want to use, MCP6S91, can only operate on positive signals, centered around a positive DC reference voltage. It has a dedicated VREF pin for this exact purpose.

There is even an example in the datasheet for a 2.5 volt DC bias:

enter image description here

pipe
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