ADC with really "True differential input"

Hi collegues.

I need ADC with really differential input and single supply.

-IN connected to reference point (REF/2)

+IN connected to input signal (+\- 2.5v)

I tried AD7684 but DataSheet tells that +IN and -IN MUST be in opposite phase to reference point. I used MCP3301 which is pin2pin compatible with AD7684 but allow any signals on inputs.

Now we need 500kS ADC and MCP3301 couldn`t achieve this.

Could you advice ADC or solution for AD7693 to adapt it to described use case.

Thank you in advance.

Parents
  • To get best performance out of an ADC with differential inputs you should be driving it with complimentary phases and common mode voltage of half the input range.

    Fixing one of the inputs to a DC level turns the converter into a single ended converter with detrimental effect on AC performance. Some parts, including the AD7684, have limitations on the common mode voltage range which are only a problem under certain circumstances.

    You have a few options here.

    - Use a ADC driver that converts your signal into a differential signal. This will give you the best performance.

    - Use a pseudo-differential ADC with the IN- attached to the ground of the signal source. This is very similar to what you are trying to do by hooking -IN to REF/2.

    - Use a single ended ADC which would work as above, but perform worse due to ground currents mixing with the signal return.

    - Find an ADC that has a wider common mode input range and use it as you were planning to. However performance won't be better than using the pseudo-differential ADC with -IN connected to the signal ground. It might be worse depending on how your REF/2 node tracks the common mode noise on your signal.

    Klaus

Reply
  • To get best performance out of an ADC with differential inputs you should be driving it with complimentary phases and common mode voltage of half the input range.

    Fixing one of the inputs to a DC level turns the converter into a single ended converter with detrimental effect on AC performance. Some parts, including the AD7684, have limitations on the common mode voltage range which are only a problem under certain circumstances.

    You have a few options here.

    - Use a ADC driver that converts your signal into a differential signal. This will give you the best performance.

    - Use a pseudo-differential ADC with the IN- attached to the ground of the signal source. This is very similar to what you are trying to do by hooking -IN to REF/2.

    - Use a single ended ADC which would work as above, but perform worse due to ground currents mixing with the signal return.

    - Find an ADC that has a wider common mode input range and use it as you were planning to. However performance won't be better than using the pseudo-differential ADC with -IN connected to the signal ground. It might be worse depending on how your REF/2 node tracks the common mode noise on your signal.

    Klaus

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