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DDC264: Apply a negative bias to the QGND pin on DDC264

Part Number: DDC264

Hi Team,

I would like to get your inputs in the customer design plan using DDC264 below:

In the customer application, they want to detect current signals from the detector array, which may have both positive and negative currents. They know that DDC264 can only detect the current that goes into the device. One possible solution is that they can apply a bias voltage to each detector, such that the total output current is always positive, which can be detected by DDC264. After checking the attached figure from the manual below, they came up with another idea: don’t need to apply a bias voltage to each detector, but they can apply a negative bias voltage to the QGND pin. Since the “-” node voltage on the operational amplifier is equal to the “+” node voltage, the “-” node also has a negative voltage. In this case, the detector is equivalently biased, and the current can be always positive, which can be detected by DDC264.


Do you think the idea to apply a negative bias voltage to QGND pin can work?

Thanks,

Jonathan

  • Hi Jonathan,

    Are we talking about a photodiode? It is probably not the case because I am not sure I understand the configurations you are talking about... But regardless, you seem to say that this detector can produce a positive or a negative current depending on the voltage across. Then I would say just do that as they originally plan (change the other terminal, the one not connected to the DDC), but don't do so by changing the QGND. QGND is internally used also respect to AGND so can't create a voltage difference there. You would have to shift all the supplies/gnds of the IC respect to the bias of the detector, which I guess is the same as moving the bias of the detector. 

    The traditional way that we recommend folks to deal with "bipolar" currents is described on this app note. But that requires an external resistor for every detector, so, if they can just get away by biasing the other terminal of the detector I would just go for that.

    Best regards,

    Edu

  • Hi Edu,

    It is about Photodetector that has both positive and negative currents.

    Thank you for this greats support. I will share this with our customer and I will let you know if this resolves their question.

    Regards,

    Jonathan