[time-nuts] No State Of The Art Counter
jmiles at pop.net
Fri Jan 7 01:35:10 UTC 2011
> > I am currently playing around with some designs in a spartan-6 and a
> > spartan-3e. The spartan-6 design has more promise resolution
> wise, but it
> > is also not very hobby friendly (bga package). So if this is ever to be
> > built using hobby level soldering skills it will be spartan-3e. The 250k
> > gates devices are available in tqfp-100 package which is doable IMO.
Actually you can even get the XC3S500Es in VQG100 flat-pack packages.
> > The timestamps are transmitted over usb to the pc for number crunching.
> > The idea is to do some curve fitting to get a frequency estimate,
> > computate Allan Deviation, and do the obligatory plots. With regard to
> > Allan Deviation, as long as I make sure the measurements have zero dead
> > time, I can compute Allan Deviation using the raw time stamps, right?
> > Also note the glaring lack of a prescaler. This can and will be
> added at a
> > later date to extend the range of the counter. For now I just
> want to get
> > the basics working properly first. On the subject of prescalers, does
> > anyone know where to order Hittite parts in low quantities? I noticed on
> > hittite.com you can place an order but if I understand correctly that is
> > only for 10+. Which is probably great if you do a group buy,
> but not if I
> > want to try out 3 of those, 2 of those, etc...
For prescaling, I'd suggest using the dividers in one of the Analog Devices
PLL parts (ADF4xxx) instead of Hittite chips. Many of the AD parts can
still be purchased in packages with actual pins, and you can always get them
in small quantities. They will also take a lot less power.
You only need to use the Hittite parts if you (a) don't have a controller of
some sort and/or (b) need lower noise or some other spec that the CMOS parts
from AD can't match.
-- john, KE5FX
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