[time-nuts] Metastability (was: Frequency Stability of Trimble Mini-T)

BriMDavis at aol.com BriMDavis at aol.com
Sun Oct 19 17:43:49 UTC 2008

Hal wrote:
>Back in those days, there was a lot of activity in designing kludgey 
>to "fix" metastability.  I could usually find the flaw.  It got boring after 
>a while.  The classic was a circuit to detect metastability and reset the 
>That reset signal would sometimes have runt pulses.

My favorite online metastability page:


This page discusses a few of those "fixes" and why they don't work,
along with some pointers to the relevant literature.

There are also some nice real-time scope shots showing
some of the various runt pulses that can occur:
"  _http://www.fpga-faq.com/Images/meta_pic_1.jpg_ 
"  _http://www.fpga-faq.com/Images/meta_pic_2.jpg_ 
"  _http://www.fpga-faq.com/Images/meta_pic_3.jpg_ 
"These are far from just delayed outputs! The end result though
"is still the same, systems that fail. But seeing these scope
"pictures of the actual Q output might make you think about how
"you measure metastability.

**************BUY Indiana Jones and the Kingdom of the Crystal Skull on DVD 

More information about the time-nuts mailing list