Common mode input voltage question about AD7622 and LTC2389-16

I have a signal with 2.6Vpp and centered around 1.3V(VCM) and a DC voltage 1.3V(VCM).

Now, I want to fetch these two source into LTC2389-16 or  AD7622  to have a differential bipolar AD conversion and remove common mode noise.

And I have some question about LTC2389-16 and AD7622 common mode input specification when the differential bipolar input  are used.

1. Can I use LTC2389-16 to do so with internal reference only(DC1826A-E) because I found that VIN- is refined to 0.5*VREF(2.048V)+-0.1V? 

2. Can I use AD7622 to do so with internal reference only(EVAL-AD76XXCBZ)? I don't find any VIN- specification when using differential bipolar input type

Thanks.

  • 0
    •  Analog Employees 
    on Aug 25, 2020 5:53 AM

    HI Timpan,

             I can see that you plan to use one differential ADC.

            1. In this question, you mean you are planning to use the internal reference as the source for the input Vref/2 in the Vin- pin, if so then I recommend having a buffer before connecting to the Vin- pin. This means that you will be operating the LTC2389 as pseudo-differential bipolar that ranges from -Vref/2 to Vref/2.

           2. The AD7622 is a true differential ADC. both Vin+ and Vin- are specified to accept voltage in the range of -0.1 to AVDD. The bipolar result of this ADC, is the result of the difference of Vin+ minus Vin- pins which will have a range of -Vref to Vref. The AD7622 true differential ADC will have a wider dynamic range. This may require single ended to differential amplifier in the front-end to maximize the dynamic range.

    Regards,

    Jonathan