AnsweredAssumed Answered

Phase and Gain measurement using AD8302

Question asked by ZhenshengTao on Apr 16, 2014
Latest reply on Apr 16, 2014 by jdobler

We used AD8302 to monitor the phase and gain difference from the PLL reference signal and PLL generated RF signal. The frequency is both ~1GHz. The setup is shown in the first attached file. We know that there is an amplitude modulation on the PLL reference, which is extracted from our fs laser. What we want to figure out is the correlation of the reference AM to the relative phase shift of the two signals. As shown in the setup figure, the monitoring (AD8302) is set out of the loop.


My first question is regarding to the precision of the phase measurement using AD8302. We want to monitor phase difference (jitter) in a very high precision (better than 0.1Deg). Is that doable with AD8302? If not, is there a good component you can recommend?


Second question is related to one of our results, which I attached to this thread. The black symbols are the direct measurement of gain-difference voltage and the blue symbols are the phase-difference voltage. A direct correlation can be observed. Especially at ~ 2hr point, I intentionally adjust the amplitude of reference, which shows a sharp jump in the gain difference measurement. It appears with phase difference measurement at the same time. Here comes my question: Is this correlation real or just an artifact generated by AD8302?

In the specs of AD8302, it says "The phase accuracy measurement is independent of signal level over a wide range" (manual p1). Could you please give me an idea of how precise this claim is? In our measurement, the gain is changed by ~1.3 dB (0.695V->0.655V). The phase changed by ~11Deg (0.99V->1.10V).


Thank you in advance.