[time-nuts] Fast frequency counting question

Didier Juges didier at cox.net
Mon May 5 23:20:51 EDT 2008


> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> Sent: Monday, May 05, 2008 8:12 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Fast frequency counting question
> Didier Juges wrote:
> >  
> >
> > I think the potential problem John is pointing out is that if the 
> > performance down to that level is driven by process 
> variations rather 
> > than by circuit design (and therefore assumed to be 
> randomly variable 
> > from unit to unit), how useful is it going to be to measure 
> the heck 
> > out of one or a few unit if you cannot statistically 
> extrapolate the 
> > results to the entire population and be able to predict yield?
> >
> > Didier KO4BB
> >
> >   
> Didier
> To come to valid conclusions on that, one needs to develop a 
> model for the effect and calibrate it against the process 
> variables etc.
> Its always possible that previous models had similar effects 
> but it hadn't been noticed.
> Bruce

I think that is the best approach, but it is easier said than done. However,
just because it is hard does not mean it should not be pursued, particularly
when considering IC manufacturing for the telecom industry. If you are not
in 6 sigma territory, you don't participate. For that kind of performance,
process control is the driving factor.

In a different domain, I am facing similar issues at my day job.
It is very hard to sort between design issues (that includes parts tolerance
issues) and manufacturing process issues (that includes machines and people
used in the manufacturing of the devices) when you only build small
quantities of anything.

All I know is that when assembly and test people are changed on the fly on a
regular basis (a staple of Lean operation), it becomes very hard to
pin-point the source of variations, but I have my opinion. We have so many
notes on the drawings of things to watch out for that people don't read
them, so we are asked to put a new note asking to read the other notes...

Didier KO4BB

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