[time-nuts] Using CPLD/FPGA or similar for frequency divider

Gerhard Hoffmann dk4xp at arcor.de
Tue Jun 2 17:42:40 EDT 2015

Am 02.06.2015 um 21:27 schrieb Tom Van Baak:
>> Is this a sensible thing to consider doing?  Or would I be better sticking to AC/HC/AHC/LVC logic?
>> Regards,
>> David Partridge
> Yes, please consider it. I would be very interested in the results.
I have made a stamp sized board that has a Xilinx 2C64 Coolrunner II, a 
1.8V regulator for the core
voltage and the programming interface for the standard Xilinx USB-cable. 
(parallel cable may work
but my laptop has no parallel port anymore.) It runs on 3.3V. All I/O pads
are fanned out to a 100 mil grid, so you can mount it easily on square 
pad board or solder it to an
unetched copper clad board. The layout is single sided plus unbroken GND 
on the bottom side.

pic = < 

(top right)

The CPLD has 64 Flipflops and enough combinational logic to feed them 
all. It runs happily
at > 200 MHZ. Two of these chips can make a 1pps from 200 MHz in, and 
another 1pps that
can be stepped in 5ns increments from -100nsec to > +1 second. A 2c64 
costs $2 or so at digikey.

BTW, the other stamps on the picture are:

top left:  Crystec CVH950 100 MHz VCXO locked to 10 MHz. I was too slow 
with those 100 MHz Wenzels this week;
               these would have justified a better effort; also sth. 
better than an 4046 ;-)

bottom left: NIST doubler from 100 MHz to 200 MHz using 2*BF862, slight 
gain, Low-Q tuned circuit
               on the output side

bottom right: 200 MHz to 400 MHz Schottky doubler, SAW filter, ERA-4 to 
bring it to 12 dBm again

The boards are home-etched; because of my daytime job my pps generator 
makes only slow progress...

A 1:1 pdf of the layout is available; one can print it to foil if one 
has a good printer (OKI 852 works
nicely) or a print shop that can do offset films will print it to 
document film for €5 to 10 per ISO A4 page+

If someone want to measure it, I can send him one of those Xilinx 
stamps; sooner or later I'll find
the time do it myself but even then the repeatability would be interesting.

Also, this morning I have published an update for my 220pV/sqrt Hz 
preamplifier; 10uF foil
capacitors one actually can buy, circuit diagrams and Gerbers for the 
adventurous. Be warned,
this version has never been fabricated, but the changes from its 
predecessor are relatively small. Most of
the work was the step to Altium Designer 15, Direct-X support on my 
virtual Win7 machine and that my
libraries from Protel-99 times desparately need some work.

The update can be found at  < 
http://www.hoffmann-hochfrequenz.de/downloads/downloads.html >.

regards, Gerhard

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