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Help with AD8302

Hi, I need to measure phase and magnitude of a signal against a reference in my project. Reading the datasheet, It seems that AD8302 evaluation board might be used for this.

I have a couple of questions that I wonder if someone can help though:

1) Both the input signal and reference are DC coupled square wave. The input signal is voltage output from a photodetector, and the reference is a output signal from the FPGA. I am wondering if I will need any additional signal conditioning before feeding siginal to AD8302?

2) Reading through other posts, it seems AD8302 becomes less accurate when the phases of the two signal are close. Can someone explain what range is considered "close"? What's the error range in this case? What the error when the phases of the two signals are, say, 90 degree apart?

Thanks in advance!

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  • It sounds like one of two things is going on:

    1) The part is broke.  I would just the supply current and the input bias levels.  There should be about 20 mA of supply current and 100mV below the positive supply bias on the inputs.

    2)  You don't have VMAG shorted to MSET and VPHS short to PSET.  If the feedback loop isn't closed, then it will act sort of like a comparator and rail.  I would measure the resistance between VMAG and MSET; same for VPHS and PSET.  It should either be close to zero or in the mega Ohm range.

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  • It sounds like one of two things is going on:

    1) The part is broke.  I would just the supply current and the input bias levels.  There should be about 20 mA of supply current and 100mV below the positive supply bias on the inputs.

    2)  You don't have VMAG shorted to MSET and VPHS short to PSET.  If the feedback loop isn't closed, then it will act sort of like a comparator and rail.  I would measure the resistance between VMAG and MSET; same for VPHS and PSET.  It should either be close to zero or in the mega Ohm range.

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