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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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  • Sorry, could you please explain first item again? I did not quite understand...

    I tried to set the two switches (SW1 and SW2) to different positions, I did see VMAG dropped from 3.7v from one position to 3.5 in the next. I measured the resistances between VMAG and MSET, VPHS and PSET, with the switches set correctly, their resistances were not zero, but both ~23K. (BTW, are the functions of these two switches to short out VMAG/MSET and VPHS/PSET?).

    However, even when I tied the ports together (VMAG and MSET), (VPHS and PSET) using cables, the VMAG output is still ~3.7V and VPHS measures ~5.2V.

    With regard to square wave, I also have another question maybe you can help -- how "similar" do these two inputs need to be -- the reference signal on INPB is out of FPGA with a series of attenuators , therefore there is a slight slope; the INPA is a output from an optical detector, it is attached to a thorlab VT1 variable terminator. If I increase VT1's setting from, say 50ohm to 500, I can boost INPA but the waveform will be more sine like due to the reduced bandwidth.

    I am using a lab DC power supply to set power to 5V. I don't really have control over current. But on the power supply LED display, it showed 0.02A... Do you think if I used wrong power supply?

    Thanks a lot!

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  • Sorry, could you please explain first item again? I did not quite understand...

    I tried to set the two switches (SW1 and SW2) to different positions, I did see VMAG dropped from 3.7v from one position to 3.5 in the next. I measured the resistances between VMAG and MSET, VPHS and PSET, with the switches set correctly, their resistances were not zero, but both ~23K. (BTW, are the functions of these two switches to short out VMAG/MSET and VPHS/PSET?).

    However, even when I tied the ports together (VMAG and MSET), (VPHS and PSET) using cables, the VMAG output is still ~3.7V and VPHS measures ~5.2V.

    With regard to square wave, I also have another question maybe you can help -- how "similar" do these two inputs need to be -- the reference signal on INPB is out of FPGA with a series of attenuators , therefore there is a slight slope; the INPA is a output from an optical detector, it is attached to a thorlab VT1 variable terminator. If I increase VT1's setting from, say 50ohm to 500, I can boost INPA but the waveform will be more sine like due to the reduced bandwidth.

    I am using a lab DC power supply to set power to 5V. I don't really have control over current. But on the power supply LED display, it showed 0.02A... Do you think if I used wrong power supply?

    Thanks a lot!

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