[time-nuts] lunatic fringe time standards

Didier Juges didier at cox.net
Thu Apr 15 08:48:40 EDT 2010


I believe Gray code was invented to support absolute mechanical position encoders, where the speed of the electronics is high compared to the speed of the hardware being monitored. It eliminates the potentially large error between two positions since only one bit changes at a time. This is done at the expense of complicated logic, which goes against speed.

I don't think Gray code has ever been used to implement fast electronic counters. That's what synchronous counters are for, and when synchronous counters are not fast enough, use a prescaler. It will just take more time to get the precision you need.

Unless you need fractional Hz resolution at THz speed, a prescaler is the way to go.

Didier

------------------------ Sent from my BlackBerry Wireless thingy while I do other things... 

-----Original Message-----
From: Eugen Leitl <eugen at leitl.org>
Date: Thu, 15 Apr 2010 13:42:00 
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] lunatic fringe time standards

On Thu, Apr 15, 2010 at 07:30:27AM -0400, Bob Camp wrote:
> Hi
> 
> I'm not 100% sure I understand exactly what you are thinking about setting up.

This is completely theoretical at this point. Just the required geometry
size would be prohibitive.
 
> My guess is that the counter needs to run at the same THz speed as 
> the oscillator. That's pretty fast. I suspect that what ever you use, 
> speed / propagation delay in the counter it's self will be an issue. 
> That will get you back to either a ripple counter or a Johnson counter. 

Wouldn't you get large errors when you caught a ripple
during readout? That wouldn't be a problem with a Gray code.
 
-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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