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
Hi
Parallel up as many inverters (or logic buffers) as you feel you need. Much less delay than the MOSFET drivers. Small packages for easy layout. Run off of 5 volts (or what ever…). Put a resistor in series with the output of each of them and they will equalize very well.
Bob
On May 17, 2012, at 7:35 PM, Michael Tharp wrote:
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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
In line with what Bob suggests, here is one of the square wave outputs
of an HP Z3816A...
http://www.xertech.net/Projects/Z3816/Output_circ.gif
Or look at the project for context...
http://www.xertech.net/Projects/Z3816/3816_mod.html
On 5/17/2012 6:17 PM, Bob Camp wrote:
Hi
Parallel up as many inverters (or logic buffers) as you feel you need. Much less delay than the MOSFET drivers. Small packages for easy layout. Run off of 5 volts (or what ever…). Put a resistor in series with the output of each of them and they will equalize very well.
Bob
On May 17, 2012, at 7:35 PM, Michael Tharp wrote:
Use the 74ABT2244: integrated resitors at the outputs.
On Fri, May 18, 2012 at 4:50 AM, Rex rexa@sonic.net wrote:
In line with what Bob suggests, here is one of the square wave outputs of
an HP Z3816A...
http://www.xertech.net/**Projects/Z3816/Output_circ.gifhttp://www.xertech.net/Projects/Z3816/Output_circ.gif
Or look at the project for context...
http://www.xertech.net/**Projects/Z3816/3816_mod.htmlhttp://www.xertech.net/Projects/Z3816/3816_mod.html
On 5/17/2012 6:17 PM, Bob Camp wrote:
Hi
Parallel up as many inverters (or logic buffers) as you feel you need.
Much less delay than the MOSFET drivers. Small packages for easy layout.
Run off of 5 volts (or what ever…). Put a resistor in series with the
output of each of them and they will equalize very well.
Bob
On May 17, 2012, at 7:35 PM, Michael Tharp wrote:
_____________**
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and follow the instructions there.
Hi
For a 50 ohm buffer, you probably want something like 200 ohms in series
with each output (4 buffers) or 400 ohms (8 buffers).
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Azelio Boriani
Sent: Friday, May 18, 2012 7:55 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Buffering a PPS signal
Use the 74ABT2244: integrated resitors at the outputs.
On Fri, May 18, 2012 at 4:50 AM, Rex rexa@sonic.net wrote:
In line with what Bob suggests, here is one of the square wave outputs of
an HP Z3816A...
http://www.xertech.net/**Projects/Z3816/Output_circ.gif<http://www.xertech.n
et/Projects/Z3816/Output_circ.gif>
Or look at the project for context...
http://www.xertech.net/**Projects/Z3816/3816_mod.html<http://www.xertech.net
/Projects/Z3816/3816_mod.html>
On 5/17/2012 6:17 PM, Bob Camp wrote:
Hi
Parallel up as many inverters (or logic buffers) as you feel you need.
Much less delay than the MOSFET drivers. Small packages for easy layout.
Run off of 5 volts (or what ever.). Put a resistor in series with the
output of each of them and they will equalize very well.
Bob
On May 17, 2012, at 7:35 PM, Michael Tharp wrote:
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e-nuts>
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On 05/18/2012 08:24 AM, Bob Camp wrote:
Hi
For a 50 ohm buffer, you probably want something like 200 ohms in series
with each output (4 buffers) or 400 ohms (8 buffers).
Yep, I ended up choosing a quad buffer with 180 ohms on each pin which
should yield 45 ohm source impedance and 27mA short-circuit current,
while the part is specified for 32mA. Thanks for pointing me in the
right direction.
-- m. tharp
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@partiallystapled.com
Sender: time-nuts-bounces@febo.com
Date: Thu, 17 May 2012 19:35:24
To: time-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of shalimr9@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@partiallystapled.com
Sender: time-nuts-bounces@febo.com
Date: Thu, 17 May 2012 19:35:24
To: time-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 05/18/2012 07:24 AM, Bob Camp wrote:
Hi
For a 50 ohm buffer, you probably want something like 200 ohms in series
with each output (4 buffers) or 400 ohms (8 buffers).
It may be worthwhile considering the gate output impedance as well. For
example, for 5V AC logic driving a 50 ohm line the initial edge from the gate is
about 4V - which implies a Zo of about 13 ohms. A 50 ohm buffer with 4 gates
would therefore use 187 ohms series resistors.
There is an app note attached here that discusses this:
--
Bob Smither Smither@c-c-i.com
---========
A well regulated Militia, being necessary to the security of a free State,
the right of the people to keep and bear Arms, shall not be infringed.
-- Second amendment to the Constitution of the united States
---========
Circuit Concepts, Inc. 281-331-2744
Be careful that you use the proper logic device for the GPS 1PPS output.
An 74AC device has a minimum HIGH input logic level of 2.1 volts when running with
a 3.0 volt VCC, and 3.65 when running at 5 volt VCC. A GPS receiver running at 3.3
volts may be on the edge. Consider using a 74F part instead as it has a lower HIGH
input requirement when running a 5 volt VCC than a 74AC.
Jerry
At 11:50 AM 5/18/2012, you wrote:
On 05/18/2012 07:24 AM, Bob Camp wrote:
Hi
For a 50 ohm buffer, you probably want something like 200 ohms in series
with each output (4 buffers) or 400 ohms (8 buffers).
It may be worthwhile considering the gate output impedance as well. For
example, for 5V AC logic driving a 50 ohm line the initial edge from the gate is
about 4V - which implies a Zo of about 13 ohms. A 50 ohm buffer with 4 gates
would therefore use 187 ohms series resistors.
There is an app note attached here that discusses this:
--
Bob Smither Smither@c-c-i.com
---========
A well regulated Militia, being necessary to the security of a free State,
the right of the people to keep and bear Arms, shall not be infringed.
-- Second amendment to the Constitution of the united States
---========
Circuit Concepts, Inc. 281-331-2744
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Jerry Mulchin