Re: [time-nuts] Buffering a PPS signal

[Hal Murray]

t...@leapsecond.com said:
> If this is for a computer and NTP then you may ignore the sawtooth.

> GPS receiver sawtooth corrections are for people working at the nanosecond
> level; important when you're working with disciplining quartz or rubidium
> oscillators with stability at the 1e-12 level.

> Computer timekeeping and NTP is a million times worse than this. 

I think you are off by a few orders of magnitude.  A million ns is a ms.  
It's easy to get NTP running much than that.

I agree that most systems running NTP are unlikely to notice the sawtooth 
correction, but this is time-nuts.

Have the PTP guys gotten good enough to notice hanging bridges yet?  (as the 
phase of their clocks  drifts)


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] Buffering a PPS signal

[Tom Van Baak]

If this is for a computer and NTP then you may ignore the sawtooth.

GPS receiver sawtooth corrections are for people working at the
nanosecond level; important when you're working with disciplining
quartz or rubidium oscillators with stability at the 1e-12 level.

Computer timekeeping and NTP is a million times worse than this.

/tvb

> I don't need the sawtooth correction done in hardware because at least 
> in my case the pulse is being fed into ntpd on a Rb-clocked computer, 
> and ntpd can add the correction itself. But I'll definitely consider a 
> bigger, better board that can do the correction internally, probably in 
> a form more generic than this board which is just an interface to the 
> Resolution SMT (and perhaps Resolution T, haven't checked if the 
> mechanical aspects are the same).
> 
> -- m. tharp



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Re: [time-nuts] Buffering a PPS signal

[Bob Camp]

Hi

If that's a concern, use a 74ACT part

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Jerry Mulchin
Sent: Friday, May 18, 2012 3:20 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Buffering a PPS signal

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:
>
>  http://c-c-i.com/node/107
>
>-- 
>Bob Smither  smit...@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
>
>
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Jerry Mulchin



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Re: [time-nuts] Buffering a PPS signal

[Jerry Mulchin]

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:
>
>  http://c-c-i.com/node/107
>
>-- 
>Bob Smither  smit...@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



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Re: [time-nuts] Buffering a PPS signal

[Bob Smither]

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:

  http://c-c-i.com/node/107

-- 
Bob Smither  smit...@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
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Re: [time-nuts] Buffering a PPS signal

[Michael Tharp]

On 05/18/2012 01:33 PM, Mark Sims wrote:


While you're at it,  add an ATMEGA328 processor and a 250 ps res/256 step delay 
line.   The processor reads the timing message,  picks off the sawtooth 
correction factor,  converts it to an 8-bit value that it output on a port to 
the delay line.  The 1PPS signal clocks the port into the delay line for 
sawtooth correction.   (This all assumes that the correction factor applies to 
the NEXT 1PPS that is output (the PPS correction is not documented...  the time 
field in the message  applies to the previous 1PPS pulse).


I don't need the sawtooth correction done in hardware because at least 
in my case the pulse is being fed into ntpd on a Rb-clocked computer, 
and ntpd can add the correction itself. But I'll definitely consider a 
bigger, better board that can do the correction internally, probably in 
a form more generic than this board which is just an interface to the 
Resolution SMT (and perhaps Resolution T, haven't checked if the 
mechanical aspects are the same).


-- m. tharp

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[time-nuts] Buffering a PPS signal

[Mark Sims]

While you're at it,  add an ATMEGA328 processor and a 250 ps res/256 step delay 
line.   The processor reads the timing message,  picks off the sawtooth 
correction factor,  converts it to an 8-bit value that it output on a port to 
the delay line.  The 1PPS signal clocks the port into the delay line for 
sawtooth correction.   (This all assumes that the correction factor applies to 
the NEXT 1PPS that is output (the PPS correction is not documented...  the time 
field in the message  applies to the previous 1PPS pulse).
Another useful feature might be a fan driver FET controlled by the computer RTS 
and DTR lines.  That way Lady Heather can do the temperature control thing...  
RTS is enable,  DTR is heat/cool.  Since a fan only cools,  you could skip 
using the RTS signal.   
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Re: [time-nuts] Buffering a PPS signal

[Bob Camp]

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-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of shali...@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 
Sender: time-nuts-boun...@febo.com
Date: Thu, 17 May 2012 19:35:24 
To: 
Reply-To: Discussion of precise time and frequency measurement
    
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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Re: [time-nuts] Buffering a PPS signal

[shalimr9]

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 
Sender: time-nuts-boun...@febo.com
Date: Thu, 17 May 2012 19:35:24 
To: 
Reply-To: Discussion of precise time and frequency measurement

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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Re: [time-nuts] Buffering a PPS signal

[Michael Tharp]

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

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Re: [time-nuts] Buffering a PPS signal

[Bob Camp]

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-boun...@febo.com [mailto:time-nuts-boun...@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  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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mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/tim
e-nuts>
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>
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Re: [time-nuts] Buffering a PPS signal

[Azelio Boriani]

Use the 74ABT2244: integrated resitors at the outputs.

On Fri, May 18, 2012 at 4:50 AM, Rex  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
>
> 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:
>>
>>
>
> __**_
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> mailman/listinfo/time-nuts
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Re: [time-nuts] Buffering a PPS signal

[Rex]

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:




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Re: [time-nuts] Buffering a PPS signal

[Bob Camp]

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
> 
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[time-nuts] Buffering a PPS signal

[Michael Tharp]

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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