[time-nuts] No State Of The Art Counter

Thu Jan 6 21:53:24 UTC 2011

Didier,

Thanks. I doubt Hittite will send me a couple of samples for "this one and
that one and oh that one", but you do raise a good point. I can always try! :)

With respect to fpga development boards, for this project I am all set! I am
currently tinkering with these two boards:

http://www.digilentinc.com/Products/Detail.cfm?Prod=NEXYS2

http://www.digilentinc.com/Products/Detail.cfm?Prod=ATLYS

Both have one of those ez-usb fx2 controllers from cypress (cy7c68013a),
which I find easy to work with under linux. Plus I already had verilog
modules from some older projects that take care of the usb fifos on the fpga
side.

As for processor, currently I use a picoblaze softcore which works for both
the spartan-3 and spartan-6. So I only have to write code for that once...

My remarks regarding the tqpf-100 package was for the benefit of those who
might be looking for something to put in a DIY counter and want to be able
to solder it themselves. Since I'm already using these development boards
for other stuff as well, I thought it would be fun to see how far one can
take these things timing resolution-wise...

I am not familiar with the Actel parts. Do you happen to know what kind of
timing granularity is possible with the carry chain or similar structures on
those Actels?

regards,
Fred

--- On Thu, 1/6/11, shalimr9 at gmail.com <shalimr9 at gmail.com> wrote:

> From: shalimr9 at gmail.com <shalimr9 at gmail.com>
> Subject: Re: [time-nuts] No State Of The Art Counter
> To: "Time-Nuts" <time-nuts at febo.com>
> Date: Thursday, January 6, 2011, 8:25 PM
> Fred,
> 
> Good luck on your project, it sounds exciting.
> 
> I have been able to get a couple of samples for free from
> Hitite. That was several years ago (before the
> recession...)
> 
> Regarding FPGA, Actel has a demo board for their
> SmartFusion device (big flash-based FPGA + Cortex M3
> processor + 256k program flash separate from the FPGA on the
> same chip, not a soft core) which has USB slave and Ethernet
> ports for about $200 in qty 1. There is also a smaller FPGA
> (ProASIC+) on the board, not sure what it is used for? I
> have one of these boards, but I have not done anything with
> it yet. It is a nice board full of potential... The chip is
> in a BGA package, but if you use this board, you don't need
> to add much, just the clock and input circuits.
> 
> Didier KO4BB
> 
> Sent from my Verizon Wireless BlackBerry
> 
> -----Original Message-----
> From: Tijd Dingen <tijddingen at yahoo.com>
> Sender: time-nuts-bounces at febo.com
> Date: Thu, 6 Jan 2011 11:02:12 
> To: <time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency
> measurement
>     <time-nuts at febo.com>
> Subject: [time-nuts] No State Of The Art Counter
> 
> To whom it may concerns,
> 
> Currently I am building a DIY frequency counter. Since this
> is my first serious counter project I am trying to keep
> things simple, hence It Will Not Be State Of The Art. Maybe
> a not-too-difficult hobby level counter will be of interest
> to some, so I'd thought I'd post here...
> 
> The architecture in a couple of bulletpoints:
> - fpga based as much as possible to keep the parts count
> down
> - coarse counters running at max 200 MHz for now
> - interpolation is done using TDC's. The TDC's look
> suspiciously much like tapped delay lines and are
> implemented inside the fpga, using mainly the carry chains.
> - 10000 continuous time stamps per second
> - 500 ps timestamp resolution. And with resolution I mean
> the smallest resolvable thingy (related to bin size), not
> precision nor accuracy.
> 
> That 500 ps is conservative. I intend to do better than
> that, but just to give some idea of the starting point...
> The main thing for now is to get a handle on the DNL of the
> TDC.
> 
> 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.
> 
> 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...
> 
> Another question for those that have already done this ...
> suppose you have a "good" 10 MHz (OCXO, GPSDO, WhateverO)
> and want to use that for your reference counter. What is a
> reasonable low cost method to end up with a 200 MHz clock in
> a spartan-3e and a 500 MHz clock in a spartan-6? I am
> currently using the fpga's internal dcm but the added jitter
> is considerable.
> 
> Since I am a newbie when it comes to this time stuff, no
> doubt there will be plenty of you that have more experience
> with implementations of counters ... so what are regular
> pitfalls I should be aware of?
> 
> Thank you for your time,
> Fred
> 
> 
>       
> 
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