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Visitor
Posts: 3
Registered: ‎05-29-2012

Jitter on main clock generator

Hi

 

My Microboard main clocks have loads of jitter. It first became apparent a few days ago when I was developing a VGA screen driver. The simple image of a vertical bar on screen showed a zipper like edge. I eventually traced this back to the clock source, CDCE913 on the Microboard. Using a digital scope to view the clocks, probing directly onto the 27MHz crystal shows a pretty steady oscillation, however when I probe the 3 clock outputs (100MHz, 66.7MHz and 40MHz, ) I see loads of clock jitter. For example probing the the 100MHz clock and triggering on the rising edge, I see 5nsec of jitter just 100nsec after the trigger point.

 

Is this a faulty board? Can someone please confirm that their boards DO / DO NOT do the same?

 

Any suggestions how to fix it?

 

Thanks

Mike

  

Avnet Employee (Star Contributor)
Posts: 605
Registered: ‎04-20-2009

Re: Jitter on main clock generator

The default CDCE913 configuration enables spread spectrum capability.  Are you using any internal FPGA clocking resources to clean up the clock?  You could always reprogram the CDCE913 to turn off the spread spectrum.

 

Bryan

Visitor
Posts: 3
Registered: ‎05-29-2012

Re: Jitter on main clock generator

Would the spread spectrum capability show up as clock jitter - just as I have described?

How can I reprogram the CDCE913. Is there an app to do this?

What resources can I use to clean up the clock and give me a stable clock to use for my application?

 

PLEASE NOTE I AM COMPLETELY NEW TO SPARTN 6 FPGA

Avnet Employee (Star Contributor)
Posts: 605
Registered: ‎04-20-2009

Re: Jitter on main clock generator

[ Edited ]

If you want, take an image of your clock measurement, and I'll let our board designer look at it.

 

To learn about cleaning up a clock inside Spartan-6, I suggest you read Xilinx UG382, or get your local Avnet FAE to teach you.

 

As far as reprogramming the CDCE913, I have projects in either 12.4 or 13.2 that do this.  I started the documentation, but it's not complete.  Hopefully what I have is enough to help you.

 

< See Below >

Bryan

Regular Visitor
Posts: 1
Registered: ‎03-26-2012

Re: Jitter on main clock generator

Hi Bryan,

 

i am interested in reprogramming the CDCE913. Unfortunately, your links do not work anymore.

It would be nice if you send it to me again.

 

Thanks

Daniel 

Avnet Employee (Star Contributor)
Posts: 605
Registered: ‎04-20-2009

Re: Jitter on main clock generator

Here are updated links:

 

Avt_S6LX9_CDCE913_12_4_02.zip
https://avnet.egnyte.com/h-s/20120709/b84d471ce2bc4522

Avt_S6LX9_CDCE913_13_1_01.zip
https://avnet.egnyte.com/h-s/20120709/1062c56de2634cc2

AvtS6LX9MicroBoard_CDCE913_Program_13_2_01_PRELIMINARY.pdf
https://avnet.egnyte.com/h-s/20120709/3b48a2a319e14d5a

 

Bryan

Visitor
Posts: 1
Registered: ‎12-03-2012

Re: Jitter on main clock generator

Bryan:

 

This is not at all clear to me. At what point are the parameters for the CDCE913 entered? Is it in the code, through the debugger, or what?

Avnet Employee (Star Contributor)
Posts: 605
Registered: ‎04-20-2009

Re: Jitter on main clock generator

It's in the MicroBlaze C code.  The LX9 hardware platform includes an I2C peripheral interfaced to the CDCE913.  The MicroBlaze then writes values into the CDCE913 registers.

Bryan

Regular Visitor
Posts: 8
Registered: ‎02-16-2013

Re: Jitter on main clock generator

I have the same problem, using so many other people vga code also output with shaking image

 

I tried to open the Avt_S6LX9_CDCE913_13_1_01 project using ISE 13.4. When i click on Generate Programming file, it pop out


The Xilinx Platform Studio (XPS) executable cannot be found by ISE. This may indicate that the Xilinx Embedded Development Kit (EDK) sofware is either not installed or ...........


Of cause, i dont have XPS, EDK, i only have ISE and SDK.

The instruction in pdf file said that it did not need EDK, how can i use this project?

Avnet Employee (Star Contributor)
Posts: 605
Registered: ‎04-20-2009

Re: Jitter on main clock generator

Have you tried going straight to SDK and only opening the SDK portion of the project?  If you want to modify the hardware platform, then you would need XPS.  However, I don't think you do.

Bryan