[time-nuts] Buffering a PPS signal

Michael Tharp gxti at partiallystapled.com
Thu May 17 23:35:24 UTC 2012


Greetings,

As I mentioned briefly a few days ago I'm working on an interface board 
for the Trimble Resolution SMT carrier board to provide a convenient way 
to get power in and PPS/serial out. The PPS output is a 3.3v, 125 
microsecond long pulse and I'd like to buffer it with something that can 
drive a 50 ohm terminated line. What's the best way to go about doing 
this? I've looked at using a MOSFET driver like FAN3111ESX but most of 
these have a moderate (30-50ns) delay with a moderate temperature 
coefficient, but perhaps I'm expecting too much.

For people interested in buying the board, it will have USB and RS-232 
(with PPS on the Carrier Detect line) plus the 50 ohm PPS output on BNC. 
Physically, it's the same size and shape as the RSMT board itself and 
will fit directly on top. Total cost should be about 20 USD.

Current schematic is here, comments welcome:
http://partiallystapled.com/~gxti/circuits/2012/05/17-piggyv2.png

Cheers,
-- m. tharp



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