Driving analog data convertor AD7823 with an op-amp

Hello,

I'm interested in using an op-amp to drive an AD7823 data convertor.

Maximum gain required is about ~30, since I can use a ref voltage as low as 1.2V on the AD7823. Required bandwidth operation is 100KHz.

I have no requirements on the op-amp except that the supply range should be between 3v to 5v. However, I do prefer to use a single supply op-amp. I'm not sure whether I should choose an op-amp with a differential output, which according to my understanding, will be more accurate (Will the AD7823 be able to work with it?) or a single ended output with a common ground to the ADC Vin- input?

After reading some application notes I became a little bit confused with all the configurations out there and would appreciate some help...

Thanks in advance,

regards,

Eyal

Parents
  • First of all, thanks for all the responses.

    I'm interested in amplifying a positive signal (between 0-50mv) from a similar photoreceiver to this one and would like to be able to utilize as much as I can of the AD7823 resolution with only a single stage amplifier.

    The signal I am interested to amplify is the photoreceiver's output which I believe is referenced to its internal ground (It is a double ended output). Unlike the device linked above, my device has a frequency bandwidth of 100KHz, but a similar output impedance of 16ohm.

    The AD8601 seems very appropriate from the frequency point view, GBWP of 8MHz. A simulation also shows that a non inverting single supply configuration with a gain of 10 (500mv = utilizing ~45% of the AD7823 resolution) works reasonably well.

    I originally had 2 concerns:

    1. At a simple non inverting gain configuration of 20 (1v = utilizing 83% of the AD7823 resolution), the  
        amplifier was further away from the ground rail, 9mv @input of 0mv. I know that this is the downside of
        single supply and will apply a positive offset voltage to the input of the op-amp together with a digital offset at the digital receiver which
        interfaces with the ADC.

    2. I am concerned that noise or cross talk from the controller of the ADC on the ground plane will interfere
       with the analog input to the op-amp if I will connect the reference of the photoreceiver to the common
       ground. A possible solution maybe using a digital and an analog ground planes connected by a trace on
       the PCB. Or, as I mentioned before, using a differential output op-amp, separating the analog signal from
       the common ground.

    Thanks again for trying to help,

    I would appreciate any technical advice and will be glad to provide more information if required.

    Eyal

    Message was edited by: Eyal Niv

Reply
  • First of all, thanks for all the responses.

    I'm interested in amplifying a positive signal (between 0-50mv) from a similar photoreceiver to this one and would like to be able to utilize as much as I can of the AD7823 resolution with only a single stage amplifier.

    The signal I am interested to amplify is the photoreceiver's output which I believe is referenced to its internal ground (It is a double ended output). Unlike the device linked above, my device has a frequency bandwidth of 100KHz, but a similar output impedance of 16ohm.

    The AD8601 seems very appropriate from the frequency point view, GBWP of 8MHz. A simulation also shows that a non inverting single supply configuration with a gain of 10 (500mv = utilizing ~45% of the AD7823 resolution) works reasonably well.

    I originally had 2 concerns:

    1. At a simple non inverting gain configuration of 20 (1v = utilizing 83% of the AD7823 resolution), the  
        amplifier was further away from the ground rail, 9mv @input of 0mv. I know that this is the downside of
        single supply and will apply a positive offset voltage to the input of the op-amp together with a digital offset at the digital receiver which
        interfaces with the ADC.

    2. I am concerned that noise or cross talk from the controller of the ADC on the ground plane will interfere
       with the analog input to the op-amp if I will connect the reference of the photoreceiver to the common
       ground. A possible solution maybe using a digital and an analog ground planes connected by a trace on
       the PCB. Or, as I mentioned before, using a differential output op-amp, separating the analog signal from
       the common ground.

    Thanks again for trying to help,

    I would appreciate any technical advice and will be glad to provide more information if required.

    Eyal

    Message was edited by: Eyal Niv

Children
No Data