[time-nuts] Buffering a PPS signal

Bob Camp lists at rtty.us
Fri May 18 16:07:58 UTC 2012


Hi

The next layer to this is stuff like over-voltage and short circuit
protection. I'd at least rate the parts so they can handle an indefinite
duration short on the output. If you have 5V and a 50 ohm source, that's
going to be about 1/2 watt going *somewhere*.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of shalimr9 at gmail.com
Sent: Friday, May 18, 2012 11:58 AM
To: Time-Nuts
Subject: Re: [time-nuts] Buffering a PPS signal

As a driver, you can look at the RS-485 drivers. Some have very temperature
stable and well controlled delays in the 10nS range, and they can drive
relatively low impedances. I do not have the P/N on hand, but if you can't
find one, let me know and I'll send you the P/N  from home.

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: Michael Tharp <gxti at partiallystapled.com>
Sender: time-nuts-bounces at febo.com
Date: Thu, 17 May 2012 19:35:24 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: [time-nuts] Buffering a PPS signal

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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