UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

cancel
Showing results for 
Search instead for 
Did you mean: 
Participant jamead
Participant
2,240 Views
Registered: ‎03-10-2009

How close does the reference clock have to be to the incoming 8B/10B data rate to lock?

I have an application where the incoming clock rate of the 8B/10B data will change by a small amount (~1%).   What may be some suggestions on how to handle the external reference clock?

0 Kudos
2 Replies
Teacher muzaffer
Teacher
2,225 Views
Registered: ‎03-31-2012

Re: How close does the reference clock have to be to the incoming 8B/10B data rate to lock?

@jamead for a communication system using 8b10b, 1% is not small. It's 10000 ppm which is very large by communication standards. Are you sure it's going to be as bad as 1% ? Normally communication systems are rate at +-100ppm range and especially an 8b10b system has good margin for effective clock recovery, ie if the clock difference between transmit & receive are at the rated max variation, the receiver can compensate for the difference.

- Please mark the Answer as "Accept as solution" if information provided is helpful.
Give Kudos to a post which you think is helpful and reply oriented.
0 Kudos
Historian
Historian
2,177 Views
Registered: ‎01-23-2009

Re: How close does the reference clock have to be to the incoming 8B/10B data rate to lock?

Looking at the 7 Series Data Sheet (DS182), table 62, there are parameters RXppmtol, which specifies the maximum tolerance in difference between the reference clock and the receive clock. Depending on the bitrate, it ranges between +/-200ppm to +/-1200ppm - both of which are WAY smaller than the 1% you are talking about (which, as @muzaffer said is 10,000ppm).

 

Basically, the GTX will lose lock and/or not be able to lock on a signal with this much bitrate variation.

 

Avrum

0 Kudos