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Design questions with ad9220 differential inputs

Category: Hardware
Product Number: ad9220
Software Version: 1

Trying to input -2.5v to 2.5v using a differential amplifier (ad8139)

At this time, in order to swing at 2.5V, FDA set VCM to 2.5V. (result is a 0V to 5V swing.)

When connect ad9220 differential input, should we connect differential opamp output positive to VINA and negative to VINB?

How do I connect REFCOM, SENSE, and VREF?


The reference voltage of 2.5V will be input externally.



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[edited by: kagoai at 8:05 AM (GMT -5) on 14 Dec 2022]
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  • Hi, 

    If your input signal is -2.5v to 2.5v then the VREF of 2.5V is correct.  Please see Table II, page 14 of the data sheet, the External Nondynamic row; connect VREF to your external 2.5V reference and SENSE to AVDD.  REFCOM should be connected to ground.  

    You are correct about connecting connect differential opamp output positive to VINA and negative to VINB, but would recommend that you consider adding Rs and Cs as illustrated in Figure 19 on page 18 of the data sheet to provide some isolation
    from transients at the A/D inputs reflecting back into the amplifier outputs.  You also need to connect the 2.5V reference to the VOCM pin of the AD8139 to set the common mode to 2.5V on the amplifier output.  The signal  at the input to the ADC will be same as the last row of Table I on page 13 of the AD9220 data sheet.  

    Regards, 

    David

Reply
  • Hi, 

    If your input signal is -2.5v to 2.5v then the VREF of 2.5V is correct.  Please see Table II, page 14 of the data sheet, the External Nondynamic row; connect VREF to your external 2.5V reference and SENSE to AVDD.  REFCOM should be connected to ground.  

    You are correct about connecting connect differential opamp output positive to VINA and negative to VINB, but would recommend that you consider adding Rs and Cs as illustrated in Figure 19 on page 18 of the data sheet to provide some isolation
    from transients at the A/D inputs reflecting back into the amplifier outputs.  You also need to connect the 2.5V reference to the VOCM pin of the AD8139 to set the common mode to 2.5V on the amplifier output.  The signal  at the input to the ADC will be same as the last row of Table I on page 13 of the AD9220 data sheet.  

    Regards, 

    David

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