background: freq of drive clock: 100Mhz DAC convert rate: 500Mhz registers: keep FR2 default setting, phase clear relative reg/bit all are set to 0. scope sample rate: 10GSPS, DC50 coupled. channel 1&2: keep free running@80Mhz with CPOW being set to 0 CPOW: channel phase offset word
description: firstly, I sample ch1&chn2 4096 point simultaneously, marked as PHASE_ORIGIN then repeatly set the phase in a way of that, 1. write 0 to CPOW 2. then sample 4096 point of CHN1 and CHN2 simultaneously, marked as PHASE_RESET 3. randomly write 0/90/180/270 to CPOW 4. then sample 4096 point of CHN1 and CHN2 simultaneously, marked as PHASE_CHANGE finally, doing a fft transform on the data, I work out the phase of CH1 and CH2, and it is reasonable the difference between phase_of_ch1 and phase_of_ch2 corresponding to the difference between CPOW-ch1 and CPOW-ch2. here are the phase-difference between ch1 and ch2: PHASE_ORIGIN: -97.757000 -97.741469 -97.695402 it is obvously the phase diff between the tow channel is -97 and remain stable.
PHASE_RESET: phase-diff phase-diff sub PHASE_ORIGIN 268.834330 366.5656 -91.242570 6.4887 -97.773648 -0.0424 -97.656695 0.0746 -97.715269 0.0160 268.820552 366.5518 268.804817 366.5361 262.374164 360.1055 268.790163 366.5215 262.239606 359.9709 262.293067 360.0244
PHASE_CHANGE: phase-diff phase-diff sub PHASE_ORIGIN -97.841896 -0.1106 -1.185842 96.5454 -97.706742 0.0245 82.364715 180.0960 262.296594 360.0279 -7.723721 90.0076 88.767826 186.4991 262.354357 360.0856 -187.712386 -89.9811 -7.799809 89.9315 172.287899 270.0192 -97.696454 0.0348 -277.743407 -180.0121 262.307632 360.0389 -277.700260 -179.9690 -97.713310 0.0180 82.276432 180.0077 -97.703496 0.0278 question: why there are a 6 degree apperanced? when making a great change to CPOW, such as 0-to-90, 0-to-180, the phase precision of AD9959 will get degradating? thanks for any answer.
Good day. If I'm not mistaken, you've measured the phase difference via FFT? Is there a way where you can measure the phase difference via oscilloscope. I'm just thinking that there would be an improvement in the measurement if it is made via oscilloscope.
Yes. Speak accurately, I want the measure the accuracy of phase setting via measuring the phase difference between the phase-change and no-phase-change sine wave.I also measured the phase diff between two no-phase-change sine wave via OSC(LECROY, 8GHZ BW, 20GSPS), the precision calculated by OSC is beyond 1 degree, as a contrast the precision of MATLAB using data sampled by OSC is about 0.1 degree. so finaly I did not do the subsequent experiments via OSC.Is there any other method to measure the phase diff? engineer in ADI had done some similar test on AD9959?In addition, when the both sine wave run freely and do not make phase change to them, the difference of phase diff is about 0.1 degree, so I think the computing method is correct and the jitter between OSC channals have little influence.thank you very much, look foward to you reply and meanwhile I will do the test via OSC.