I am trying to use the AD8348 evaluation board to detect the phase of a sinusoidal input signal, but have not been able to do so. I would really appreciate it if someone could help pinpoint what I am doing wrong.
My steps were the following:
1. Connected a 200 mVpp, 100 MHz sine signal to the single-ended local oscillator (LO) port. From the same function generator, sent a 200 mVpp 50 MHz signal to the single-ended MXIP port. I made sure to set SW12 to the MX position.
2. Powered the Vs pin with around 4V (within the suggested range), and set SW11 to Enable.
3. Hooked up IOPP, IOPN, QOPP, and QOPN to 1.9 MHz low pass filters, and monitored this conditioned signal on an oscilloscope. They are all DC signals.
I expect the signal QOPP-QOPN to be of the form Asin(phi), and IOPP-IOPN to be in the form Acos(phi), where phi is the phase offset of the MXIP sine input with respect to the LO input. (I set this phase shift on my function generator). Therefore, I would expect that if I take the arctangent of (QOPP-QOPN)/(IOPP-IOPN), I will get exactly this phase back. However, the results I get are not at all the phase offset I set. In fact, neither QOPP-QOPN nor IOPP-IOPN are sinusoidal. For example, I graphed IOPP-IOPN against the phase offset I set with my function generator, and got a choppy, piecewise function that had a period of 180 degrees.
Am I missing something? Thanks for all your help and input!