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Adjust DC offset using OP-Amp to feed positive ADC

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Op-amp help

Hi, i have a project to convert audio signal to digital signal, so i decided to use ADC. The signal after ADC doesn't have negative part, is there any suggestion to adjust the DC offset using op-amp. I am using digilentinc, AIO1 board.

Thank you very much
 

Op-amp help

The ADC is an AD7823. This is a unipolar part. Valid analog input voltages must be positive and be in the range of 0V to VRef. It as two input pins and they call it pseudo-differential, but it really cannot measure any negative voltages. Typical circuits have the Vin- input connected to ground.

To use this device, you must offset the audio signal with a DC voltage level to insure that in never drops below ground. There are lots of different op-amp circuits that can do this. Do an google search on the op-amp level shifter. Below is one hit.

https://www.daycounter.com/Circuits/OpAmp-Level-Shifter/OpAmp-Level-Shifter.phtml
 

Re: Op-amp help

You can try to bias the input of the ADC right in the middle of its range and then couple the audio signal through a capacitor. All you need then is make sure the cap is large enough for the lowest frequency and also make sure the signal does not exceed the range of the A/D, that is, the peak to peak amplitude of the signal must be less than the range of the A/D.
 

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