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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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  • To make sure the switch are good, can you measure the resistance from R5 to R7 on the VMAG side (either side of the resistors should be OK) and then from R6 to R8 for the VPHS side?  These measurements should be nearly 0 Ohms, near 1 or 2 Ohms.

    Then, can you test with 2 sine waves applied to the input of different amplitudes?  One at -30 dBm and the other 10 dB larger or smaller?

    Finally, can you put 100 pF caps on on C2 and C8.  That might help a bit.

    Also, try measuring VMAG and VPHS with a multimeter, instead of an oscilloscope.  The output stage might not like seeing a 50 Ohm cable then a 1meg input to the scope.

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  • To make sure the switch are good, can you measure the resistance from R5 to R7 on the VMAG side (either side of the resistors should be OK) and then from R6 to R8 for the VPHS side?  These measurements should be nearly 0 Ohms, near 1 or 2 Ohms.

    Then, can you test with 2 sine waves applied to the input of different amplitudes?  One at -30 dBm and the other 10 dB larger or smaller?

    Finally, can you put 100 pF caps on on C2 and C8.  That might help a bit.

    Also, try measuring VMAG and VPHS with a multimeter, instead of an oscilloscope.  The output stage might not like seeing a 50 Ohm cable then a 1meg input to the scope.

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