Hi,
We make RE test for DS90UB947-Q1,Result:below standard at 450MHz,The picture is waveform for result。Please share me some improved method,Thanks a lot!
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Hi,
We make RE test for DS90UB947-Q1,Result:below standard at 450MHz,The picture is waveform for result。Please share me some improved method,Thanks a lot!
Hi,
The simplest way would be to use a REFCLK that has spread spectrum capability. 0.5 % spreading with triangular modulation at about 30kHz should do the trick. SiTime 9005 series has worked for me in the past.
Other alternatives:
Cover the shield box seam with copper tape. Cover the cable entry point with copper tape, extending 0.5” onto the cable.
Adjust the bend radius of the cable as it makes the turn from the 1 meter straight segment to connect to the shield boxes.
Try a higher performance cable. Only use new cables with less than 10 connector insertions.
Try different shield box positions and orientations.
Try different DC cable routing and cable lengths. Generally shorter is better, but exceptions to that have been observed.
Many standards allow a clamp-on ferrite on the DC power cable inside the shield box.
Mike
Hi,
How to use a REFCLK that has spread spectrum capability.Can you describe it in detail?Thanks a lot!
Hi,
In my reference designs I use a 2mm x 2.5mm clock. When I want a SSC, I order from Epson or SiTime or similar. They have the standard footprints; all you have to do is replace your clock with their SSC. No PCB layout changes if you use a standard size and pinout.
VDD: 1.8V
Size: 2mm x 2.5mm
Spread type: Downspread and Triangular
Spreading rate: about 30kHz
Spread %: 0.5
If you talk to their apps engineers they can get you a part number based on your requirements, and also get you samples to test.
Mike