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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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  • Thanks. I did have the switches shown in your pic. If the other way around, the resistances were in M ohm range. Bit there was no impact on the outputs either way.

     

    Is the power supply I attached in the previous reply OK?

     

    When I adjusted the power supply voltage, from 4v to 5v, the output changed the same way (from 4v to 5v).

     

    I bought another board last Friday. During the first test, (no input, only power), when I first connected VMAG to scope (using a SMA->BNC converted and BNC cable to scope), VMAG reading was 900mv. When I switchted to VPHS, the reading was 5V. After 10min, when I changed back to VMAG, VMAG reading was 5v also!

     

    I am really at a lost what is going on here... Really need your help...

     

    I am attaching some pictures of how I did the test... One thing I just noticed was that there is a small spot on the AD8302 chip (last picture)

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  • Thanks. I did have the switches shown in your pic. If the other way around, the resistances were in M ohm range. Bit there was no impact on the outputs either way.

     

    Is the power supply I attached in the previous reply OK?

     

    When I adjusted the power supply voltage, from 4v to 5v, the output changed the same way (from 4v to 5v).

     

    I bought another board last Friday. During the first test, (no input, only power), when I first connected VMAG to scope (using a SMA->BNC converted and BNC cable to scope), VMAG reading was 900mv. When I switchted to VPHS, the reading was 5V. After 10min, when I changed back to VMAG, VMAG reading was 5v also!

     

    I am really at a lost what is going on here... Really need your help...

     

    I am attaching some pictures of how I did the test... One thing I just noticed was that there is a small spot on the AD8302 chip (last picture)

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