ADPD4000 differential input configuration

Hi, 

I am considering to use ADPD4000 in our product and mainly interested in the differential pair configuration when connecting photodiode (PD) to input pins of ADPD4000.

According to datasheet, it is obviously possible to configure differential input of PD, but it seems there is no application example in the datasheet.

I wonder it is enough to just connect the cathode & anode of PD to Input pairs (e.g., IN1 & IN2) with a biasing configuration, or if there are any advices.

For instance, the below configuration would be valid?

At IN1 pin -> PD cathode: Biasing = VC1 = TIA_VREF + 250 mV

At IN2 pin -> PD anode: Biasing = TIA_VREF

In addition, are there any difference between bias connecting to TIA-side TIA_VREF (above configuration) or IN2-side TIA_VREF?

Thank you so much.

Regards,

Seongjun

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  • +1
    •  Analog Employees 
    on Nov 11, 2019 7:46 PM

    Hello,

    The block diagram you show is more to illustrate the different connections available to the amplifiers, but it does not show all the connections that may be available at a specific instant in time. For example, if you're connecting a PD across a diff pair of inputs, you would not be able to also connect VC1 to an input as you show in your diagram. If connecting a PD differentially, then there will be 0V bias across the PD. The only way to apply that ~250mV across the PD is to configure the device in single ended mode, connect the anode to one of the inputs, and the VC pin to the cathode.

    Regards,

    Kevin

Reply
  • +1
    •  Analog Employees 
    on Nov 11, 2019 7:46 PM

    Hello,

    The block diagram you show is more to illustrate the different connections available to the amplifiers, but it does not show all the connections that may be available at a specific instant in time. For example, if you're connecting a PD across a diff pair of inputs, you would not be able to also connect VC1 to an input as you show in your diagram. If connecting a PD differentially, then there will be 0V bias across the PD. The only way to apply that ~250mV across the PD is to configure the device in single ended mode, connect the anode to one of the inputs, and the VC pin to the cathode.

    Regards,

    Kevin

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