really slow PLL...

On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s
not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?

If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John

Yeah, that sounds like the ticket to me also. Trying to use each box\'s
system clock for purposes of keeping \"user-space\" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.

At minimum it likely won\'t scale very well. Why implicitly discourage
one\'s customers from buying only a limited number of units
 
Gerhard Hoffmann wrote:
Am 21.07.22 um 13:19 schrieb jlarkin@highlandsniptechnology.com:


Where does the 10 MHz come from?

Choise of implementer. One local clock generator is needed.
This clock determines short term stabiity and phase noise.

My Lucent KS24361 uses 5 MHz MTI-260 double ovens; for
redundancy/holdover it has a 2nd unit with another crystal
oven without a receiver.

The redundancy units were really hard to sell without the
receiver; that\'s why I have 20 of these MTI-260, got a good
price. :)

They were new old stock built by HP/Agilent for Lucent as
replacement parts. They have never been on a telecom tower
in China like most of those one gets on ebay.

I have expanded the Lucent to 10 MHZ and with a distribution
amplifier:

   http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf 

cheers, Gerhard

I wonder if there\'s an advantage to using the closure phase for an array
that large. With 17 oscillators you\'ve got 136 independent phase
differences, so maybe there\'s a way to get 22 dB instead of 12 dB
improvement.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.

but they are anot free runnign are they? they are all reacting to midi
 
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible.  However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.

Using the nuts & bolts system clock for synchronization of \"user tasks\"
also makes me uncomfortable, if the device behavior only need to align
to the millisecond why not trigger them using some simple network
protocol and let their hardware figure out how long a millisecond is
independently. Do the timings of these boxes need to be tighter than the
Maple Leaf Rag?


Given that it\'s so simple to do it right, why not do that?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.

but they are anot free runnign are they? they are all reacting to midi

There\'s a system clock in each one surely but they don\'t try to sync
their system clocks, they receive an instruction \"do X for Y ms\" and
their processor figures out how long Y ms is, and does it for that long.

It is literally good enough for rock & roll, but whether it\'s good
enough for power supply sequencing IDK, there is gonna be some latency.

HP used to have GPIB on their power supplies, I\'ve never used it but I
expect it wasn\'t really useful for tight synchronization.
 
On Thu, 21 Jul 2022 09:27:39 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than 152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.

That\'s better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.


Absolutely. The scary 152 dB number doesn\'t mean that doing something
like that is automatically a bad idea.

Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)

Cheers

Phil Hobbs

I like thermostats, single-bit-feedback control loops.

We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it\'s above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it\'s cooler than the
setpoint, step fan speed down. There\'s no acoustic drama and it\'s
perfectly stable.

It dithers around the setpoint but nobody notices.

This is immune to classic control theory so the concept annoys some
people but it works great.

A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it\'s highly resistant to variations in the _plant_.

Your furnace doesn\'t go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there\'s lots of
opening and closing of doors and ovens.

Cheers

Phil Hobbs

My power supply box has 8 plugin modules of various types. Some don\'t
need much air but some really do. The two big fans are howlers at 48
volts.

Each module can present one bit to the motherboard software: I want
more air, or I don\'t. If any board wants more, ratchet the fans up a
bit. If none want more, jog the fans down.
 
On Thu, 21 Jul 2022 09:36:31 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible.  However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.

Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to
determine the right amount to tweak it by better than that.
(especially over longer timebases)

That\'s better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.

Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first
second. After that you have a good idea of how many seconds you can free
run for without having any ambiguities from residual drift.

This is an ancient trick from physics which avoids the smartest students
from having to laboriously count every pendulum swing when determining g
to maximum possible precision in a given time. It used to be (and
probably still is a favourite exam practical). Components needed are
very cheap and the whole thing is a good test of experimental technique.


It\'s not as efficient as \'dry labbing\'. ;)

We cut our EE labs and went sailing or something, and faked all the
reports one night at the end of the semister. Of course we got As.
 
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s
not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?

If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John

Yeah, that sounds like the ticket to me also. Trying to use each box\'s
system clock for purposes of keeping \"user-space\" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.

At minimum it likely won\'t scale very well. Why implicitly discourage
one\'s customers from buying only a limited number of units

Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.

The controller in each box is a MicroZed and doesn\'t support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.

Besides, what I do is design things.
 
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 09:27:39 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than 152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.

That\'s better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.


Absolutely. The scary 152 dB number doesn\'t mean that doing something
like that is automatically a bad idea.

Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)

Cheers

Phil Hobbs

I like thermostats, single-bit-feedback control loops.

We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it\'s above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it\'s cooler than the
setpoint, step fan speed down. There\'s no acoustic drama and it\'s
perfectly stable.

It dithers around the setpoint but nobody notices.

This is immune to classic control theory so the concept annoys some
people but it works great.

A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it\'s highly resistant to variations in the _plant_.

Your furnace doesn\'t go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there\'s lots of
opening and closing of doors and ovens.

Cheers

Phil Hobbs

My power supply box has 8 plugin modules of various types. Some don\'t
need much air but some really do. The two big fans are howlers at 48
volts.

Each module can present one bit to the motherboard software: I want
more air, or I don\'t. If any board wants more, ratchet the fans up a
bit. If none want more, jog the fans down.

Yup. We do the Class H supplies for our TEC driver boards like that--if
the linear amp rails, immediately jack up the supply by 0.5 V or so,
then gradually ramp it down again. We could use two ADC channels, of
course, but one comparator is simpler and works very well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 7/21/2022 10:26 AM, Phil Hobbs wrote:
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible.  However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.

Using the nuts & bolts system clock for synchronization of \"user
tasks\" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to be
tighter than the Maple Leaf Rag?


Given that it\'s so simple to do it right, why not do that?

Cheers

Phil Hobbs

If there\'s a way to get by letting each box synchronize to GPS on its
own and then using some simple network protocol to sequence them that\'s
what I\'d do, yeah.

Trying to get their system clocks to sync up over a cable makes me
uncomfortable, why do they need to share info about their inner lives.
 
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.

but they are anot free runnign are they? they are all reacting to midi

There\'s a system clock in each one surely but they don\'t try to sync
their system clocks, they receive an instruction \"do X for Y ms\" and
their processor figures out how long Y ms is, and does it for that long.

It is literally good enough for rock & roll, but whether it\'s good
enough for power supply sequencing IDK, there is gonna be some latency.

HP used to have GPIB on their power supplies, I\'ve never used it but I
expect it wasn\'t really useful for tight synchronization.

The Group Execute Trigger command does allow quite tight synchronisation
between different GPIB devices.

John
 
On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s
not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?

If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John

Yeah, that sounds like the ticket to me also. Trying to use each box\'s
system clock for purposes of keeping \"user-space\" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.

At minimum it likely won\'t scale very well. Why implicitly discourage
one\'s customers from buying only a limited number of units

Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.

The controller in each box is a MicroZed and doesn\'t support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.

Besides, what I do is design things.

So if it works fine in one box why can\'t you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.

If they\'re all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency
but syncing a bunch of boxes within a ms doesn\'t seem unreasonable.

It\'s at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.
 
bitrex wrote:
On 7/21/2022 10:26 AM, Phil Hobbs wrote:
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup,
and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at
least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low
pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible.  However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s
possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t
all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better
than 152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay
synced together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.

Using the nuts & bolts system clock for synchronization of \"user
tasks\" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to
be tighter than the Maple Leaf Rag?


Given that it\'s so simple to do it right, why not do that?

Cheers

Phil Hobbs


If there\'s a way to get by letting each box synchronize to GPS on its
own and then using some simple network protocol to sequence them that\'s
what I\'d do, yeah.

Trying to get their system clocks to sync up over a cable makes me
uncomfortable, why do they need to share info about their inner lives.

And to think you went to art school.

Cheers

Phil Hobbs
 
On Thu, 21 Jul 2022 11:11:56 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 09:27:39 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than 152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.

That\'s better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.


Absolutely. The scary 152 dB number doesn\'t mean that doing something
like that is automatically a bad idea.

Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)

Cheers

Phil Hobbs

I like thermostats, single-bit-feedback control loops.

We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it\'s above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it\'s cooler than the
setpoint, step fan speed down. There\'s no acoustic drama and it\'s
perfectly stable.

It dithers around the setpoint but nobody notices.

This is immune to classic control theory so the concept annoys some
people but it works great.

A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it\'s highly resistant to variations in the _plant_.

Your furnace doesn\'t go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there\'s lots of
opening and closing of doors and ovens.

Cheers

Phil Hobbs

My power supply box has 8 plugin modules of various types. Some don\'t
need much air but some really do. The two big fans are howlers at 48
volts.

Each module can present one bit to the motherboard software: I want
more air, or I don\'t. If any board wants more, ratchet the fans up a
bit. If none want more, jog the fans down.


Yup. We do the Class H supplies for our TEC driver boards like that--if
the linear amp rails, immediately jack up the supply by 0.5 V or so,
then gradually ramp it down again. We could use two ADC channels, of
course, but one comparator is simpler and works very well.

Cheers

Phil Hobbs

A TEC driver doesn\'t mind a little lag on its supply rail being
ratcheted up. My boards, as they heat up, also don\'t mind a little lag
in the air flow being modulated. The fan control slew time can be in
the ballpark of the thermal time constants.

Each board will have one or more temp sensors, and a resident cal
table in eeprom that has the temperature targets. Simple.
 
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

bitrex wrote:
On 7/21/2022 10:26 AM, Phil Hobbs wrote:
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup,
and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at
least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low
pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible.  However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s
possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t
all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better
than 152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay
synced together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.

Using the nuts & bolts system clock for synchronization of \"user
tasks\" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to
be tighter than the Maple Leaf Rag?


Given that it\'s so simple to do it right, why not do that?

Cheers

Phil Hobbs


If there\'s a way to get by letting each box synchronize to GPS on its
own and then using some simple network protocol to sequence them that\'s
what I\'d do, yeah.

Trying to get their system clocks to sync up over a cable makes me
uncomfortable, why do they need to share info about their inner lives.

And to think you went to art school.

Cheers

Phil Hobbs

Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.

One other thing I see a lot is undue respect for standards. As in \"you
can\'t do that because it violates SCPI standards.\" Where are the SCPI
Police when you need them?
 
Am 21.07.22 um 16:15 schrieb Phil Hobbs:

I wonder if there\'s an advantage to using the closure phase for an array
that large.  With 17 oscillators you\'ve got 136 independent phase
differences, so maybe there\'s a way to get 22 dB instead of 12 dB
improvement.

-v ?

what do you mean with closure phase? Where do the 22 dB come
from?

The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.

> Cheers
Gerhard
 
On Thu, 21 Jul 2022 11:36:01 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s
not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?

If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John

Yeah, that sounds like the ticket to me also. Trying to use each box\'s
system clock for purposes of keeping \"user-space\" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.

At minimum it likely won\'t scale very well. Why implicitly discourage
one\'s customers from buying only a limited number of units

Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.

The controller in each box is a MicroZed and doesn\'t support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.

Besides, what I do is design things.



So if it works fine in one box why can\'t you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.

If they\'re all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency
but syncing a bunch of boxes within a ms doesn\'t seem unreasonable.

It\'s at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.

The BNC would be 1 PPS pulses. They could come from GPS if it\'s
available, or one of the boxes could output the 1 PPS and the others
would sync to that.

When we designed the box, we added two BNCs, open drain drivers with
weak pullups and schmitt receivers, connected into our FPGA. We didn\'t
know what they were for, but they turn out to be handy.

One is START RUNNING YOUR SEQUENCES NOW and the other is the 1 PPS
lock. That should work.

Each module has a sequencer table in its local fpga RAM, sort of a
primitive program with 5 opcodes. A table entry can write any other
register in the FPGA, ie do anything, and one command is WAIT UNTIL,
against the 1 MHz start counter.

Customers can write fairly simple SCPI script files to program events
in each module, load them up, and fire off a shot and keep the whole
experiment time synchronized forever.

All we want to do is revolutionize the power supply business.

It\'s actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.
 
On 7/21/2022 12:09 PM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:36:01 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:

On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s
not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?

If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John

Yeah, that sounds like the ticket to me also. Trying to use each box\'s
system clock for purposes of keeping \"user-space\" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.

At minimum it likely won\'t scale very well. Why implicitly discourage
one\'s customers from buying only a limited number of units

Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.

The controller in each box is a MicroZed and doesn\'t support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.

Besides, what I do is design things.



So if it works fine in one box why can\'t you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.

If they\'re all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency
but syncing a bunch of boxes within a ms doesn\'t seem unreasonable.

It\'s at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.

The BNC would be 1 PPS pulses. They could come from GPS if it\'s
available, or one of the boxes could output the 1 PPS and the others
would sync to that.

When we designed the box, we added two BNCs, open drain drivers with
weak pullups and schmitt receivers, connected into our FPGA. We didn\'t
know what they were for, but they turn out to be handy.
I see.

One is START RUNNING YOUR SEQUENCES NOW and the other is the 1 PPS
lock. That should work.

Each module has a sequencer table in its local fpga RAM, sort of a
primitive program with 5 opcodes. A table entry can write any other
register in the FPGA, ie do anything, and one command is WAIT UNTIL,
against the 1 MHz start counter.

Customers can write fairly simple SCPI script files to program events
in each module, load them up, and fire off a shot and keep the whole
experiment time synchronized forever.

Gotcha

> All we want to do is revolutionize the power supply business.

Sounds good

It\'s actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.

I\'m just sayin there\'s also a standard (uh oh!) dating back to the 50s
for synchronizing equipment using time-code:

<https://en.wikipedia.org/wiki/IRIG_timecode>

up to 10,000 pulses per second. I understand now that there\'s no
facility to program or sequence one box from the others they each run
their own \"script\" from memory.

It would seem simpler to flip a switch to designate one box as the
master and have the others watch a timecode it sends out at a higher
resolution than the desired sync error. If the master then needs to
itself be synced to real-world time via a GPSDO then ah...well I guess
there should\'ve been a 3rd BNC :-(
 
Gerhard Hoffmann wrote:
Am 21.07.22 um 16:15 schrieb Phil Hobbs:

I wonder if there\'s an advantage to using the closure phase for an
array that large.  With 17 oscillators you\'ve got 136 independent
phase differences, so maybe there\'s a way to get 22 dB instead of 12
dB improvement.

-v ?

what do you mean with closure phase? Where do the 22 dB come
from?

The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.

Cheers
Gerhard

Sure. Thing is, that wastes a lot of information that you could maybe
use to get 10*log(136) = 21.3 dB improvement instead of 10*log(17) =
12.3 dB. [136 = N(N-1)/2 when N = 17.]

Closure is a really cute idea, which I first came across in the context
of very long baseline interferometry (VLBI) radio telescopes. See the
discussion from BEOS 3e here:

<https://electrooptical.net/www/sed/closure.png>.

It\'s on P. 341 of BEOS 3e and P. 385 of BEOS 2e for those who have copies.

I don\'t have a scheme right handy, but it works at DC for measuring
noise by the correlation method, where N meters get you 20 log N - 6 dB
improvement.

It seems like it might be worth a bit of chasing, especially (as you
say) in the regime where any improvement becomes very difficult to get.
It would make an interesting paper if nobody\'s done it already.

Cheers

Phil Hobbs
--

Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.

but they are anot free runnign are they? they are all reacting to midi

There\'s a system clock in each one surely but they don\'t try to sync
their system clocks, they receive an instruction \"do X for Y ms\" and
their processor figures out how long Y ms is, and does it for that long.

It is literally good enough for rock & roll, but whether it\'s good
enough for power supply sequencing IDK, there is gonna be some latency.

HP used to have GPIB on their power supplies, I\'ve never used it but I
expect it wasn\'t really useful for tight synchronization.

The Group Execute Trigger command does allow quite tight synchronisation
between different GPIB devices.

GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get 500kb/s.
It\'s best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).

Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB
devices were rather pedestrian at accepting commands.

IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC
9801 PC\'s in Japan although hardly ever used by their customers.

The cables and connectors could only be described as a bit clunky!
They really didn\'t get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...

--
Regards,
Martin Brown
 

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