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Guest

Mon Jan 07, 2019 11:45 am   



I wrote:

Quote:
The old way I did things like that was also clock-less:
ADC-8-bits -> address-EPROM-data -> DAC.
Conversion table in EPROM [1].
There is then still some noise, as bits do not always appear on the EPROM output at the same time,
there are time differences in address lookup, but 't works.
For a wider bus use 2 EPROMS for 16 bits etc.

[1] EPROMS were those chips with a little window where you could see the silly-con and give it a sun-tan
to make it lose its memory. I still have some 2732 around somewhere and an UV tube.


PS
I would not even bother with a DAC.
For tuning, fine tuning that is, an EPROM output with an R2R network as DAC
for 256 steps should do, followed by a lowpass.
If the EPROM logic output levels are not really CMOS Vss and Vdd,
then use a CMOS buffer.
Some resistors from the same batch.
Clock, what clock?
Done it for video with R2R on FPGA output, works great.

Winfield Hill
Guest

Mon Jan 07, 2019 6:45 pm   



<698839253X6D445TD_at_nospam.org> wrote...
Quote:

PS
I would not even bother with a DAC.
For tuning, fine tuning that is, an EPROM output with
an R2R network as DAC for 256 steps should do ...


But a small cheap DAC is so tempting. I started with
a PWM signal filtered with Stephen Woodward's trick,
for my MPX-16H DAQ ** and finally realized an honest
DAC made more sense, and updated the PCB to an MCP4921,
a 12-bit DAC in an SOIC-8 package, only $1.50 qty100.

** MPX-16H bare boards, free, winfieldhill_at_yahoo.com
https://www.dropbox.com/sh/41r9wwgqo7rk3lw/AACKDkCKKJRq8DUvSSfQWkv0a?dl=0


--
Thanks,
- Win


Guest

Mon Jan 07, 2019 8:45 pm   



On a sunny day (7 Jan 2019 09:23:44 -0800) it happened Winfield Hill
<hill_at_rowland.harvard.edu> wrote in <q101v00i0r_at_drn.newsguy.com>:

Quote:
698839253X6D445TD_at_nospam.org> wrote...

PS
I would not even bother with a DAC.
For tuning, fine tuning that is, an EPROM output with
an R2R network as DAC for 256 steps should do ...

But a small cheap DAC is so tempting. I started with
a PWM signal filtered with Stephen Woodward's trick,
for my MPX-16H DAQ ** and finally realized an honest
DAC made more sense, and updated the PCB to an MCP4921,
a 12-bit DAC in an SOIC-8 package, only $1.50 qty100.

** MPX-16H bare boards, free, winfieldhill_at_yahoo.com
https://www.dropbox.com/sh/41r9wwgqo7rk3lw/AACKDkCKKJRq8DUvSSfQWkv0a?dl=0


Yes, sure, but that is a serial SPI input DAC that needs a clock, and a micro.
he wants no clock?

The R2R, or if you are brave 8 resistors ratio 1,2,4,8,..128,

on the output of an EPROM data bus, well lemme draw something:

http://panteltje.com/pub/EPROM_and_R2R_and_varicap_IMG_6710.JPG

Resistors are cheap, leaves him more money for skying.

Flash ADCs are fast, not so many bits,,, like your 24 ! That is amazing.

I have never used a 'duino in my life Wink

Piotr Wyderski
Guest

Mon Jan 07, 2019 9:45 pm   



John Larkin wrote:

Quote:
We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise.


Not sure if I understand correcty, but whenever there is a discrete
level change, there will inevitably be some injection of phase noise.
So what are you trying to avoid?

Best regards, Piotr

John Larkin
Guest

Mon Jan 07, 2019 9:45 pm   



On Mon, 7 Jan 2019 21:25:49 +0100, Piotr Wyderski
<peter.pan_at_neverland.mil> wrote:

Quote:
John Larkin wrote:

We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise.

Not sure if I understand correcty, but whenever there is a discrete
level change, there will inevitably be some injection of phase noise.
So what are you trying to avoid?

Best regards, Piotr


DAC major bit glitches maybe.

It's more interesting of the comparator gains are low.

It was just a passing idea.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com


Guest

Mon Jan 07, 2019 9:45 pm   



John Larkin wrote:
Quote:
It would be tough to make a real 8-bit DAC out of resistors and CMOS
levels.


Why? Works perfectly, R2R is as old as the world:
https://en.wikipedia.org/wiki/Resistor_ladder

Got nice video from it (on output of Xilinx FPGA),
driving straight into an emitter follower and then a 75 Ohm cable,


Guest

Mon Jan 07, 2019 9:45 pm   



On Monday, 7 January 2019 20:16:05 UTC, John Larkin wrote:

Quote:
It would be tough to make a real 8-bit DAC out of resistors and CMOS
levels.


Assuming you use 0.1% Rs, is CMOS R_out the problem?


NT

John Larkin
Guest

Mon Jan 07, 2019 9:45 pm   



On Mon, 07 Jan 2019 19:12:14 GMT, <698839253X6D445TD_at_nospam.org>
wrote:

Quote:
On a sunny day (7 Jan 2019 09:23:44 -0800) it happened Winfield Hill
hill_at_rowland.harvard.edu> wrote in <q101v00i0r_at_drn.newsguy.com>:

698839253X6D445TD_at_nospam.org> wrote...

PS
I would not even bother with a DAC.
For tuning, fine tuning that is, an EPROM output with
an R2R network as DAC for 256 steps should do ...

But a small cheap DAC is so tempting. I started with
a PWM signal filtered with Stephen Woodward's trick,
for my MPX-16H DAQ ** and finally realized an honest
DAC made more sense, and updated the PCB to an MCP4921,
a 12-bit DAC in an SOIC-8 package, only $1.50 qty100.

** MPX-16H bare boards, free, winfieldhill_at_yahoo.com
https://www.dropbox.com/sh/41r9wwgqo7rk3lw/AACKDkCKKJRq8DUvSSfQWkv0a?dl=0

Yes, sure, but that is a serial SPI input DAC that needs a clock, and a micro.
he wants no clock?

The R2R, or if you are brave 8 resistors ratio 1,2,4,8,..128,

on the output of an EPROM data bus, well lemme draw something:

http://panteltje.com/pub/EPROM_and_R2R_and_varicap_IMG_6710.JPG

Resistors are cheap, leaves him more money for skying.


With season passes to Sugar Bowl and Tahoe Donner, incremental skiing
is free. Well, I do have to pay for the mid-day rum+coke.

I was thinking of the weird dac as an IC in a TCXO, but generally just
thinking of a physically linear delta-sigma thing.

It would be tough to make a real 8-bit DAC out of resistors and CMOS
levels.

You might also sum a large number of bad (2 or 3 bit) DACs to get sort
of the same effect I was considering.

There are some DACs that implement their three MSBs as 8
equally-weighted resistors.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Piotr Wyderski
Guest

Mon Jan 07, 2019 10:45 pm   



John Larkin wrote:

> DAC major bit glitches maybe.

Now it makes sense, thanks!

Best regards, Piotr

Phil Hobbs
Guest

Mon Jan 07, 2019 10:45 pm   



On 1/5/19 2:47 PM, John Larkin wrote:
Quote:
On Sat, 05 Jan 2019 19:12:25 GMT, <698839253X6D445TD_at_nospam.org
wrote:

John Larkin wrote
We were talking about TCXOs. One measures temperature and drives a
varicap through some nonlinear transfer function to get minumum net
TC.

We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise. I guess you could use a static
polynomial with the equivalent of nonvolatile DPOTS as the
coefficients.


This occurred to me, not as anything practical maybe but as an
interesting architecture.

https://www.dropbox.com/s/8ls632mndcxqby8/DAC_TCXO.JPG?raw=1

It's sort of a thermometer-code ADC, but each comparator incrementally
adds + or - one increment to the output.

As the temperature increases, we jog the output up or down one
increment at a time.

The sequence of switch settings become a delta-sigma code to make the
output.

The comparators could be sort of linear, not step outputs, to kind of
interpolate a bit. Some flash ADCs did something like that, soft
comparators.

Yes,
but you can get more linear varicap effect by using for example 2.
This paper shows some topologies and their effect:
https://www.everythingrf.com/uploads/whitepapers/IEEE_BCTM_092010_2.pdf

Then use a linear opamp feedback loop?

I am using something like fig 1b on page 3 for my 25 MHz PLL reference for Eshail2.

A TCXO wouldn't need a very linear varactor, but a tight PLL does.


Doesn't have to be super duper linear, though +-10% is lots tight
enough, because all it does is change the loop gain a bit. You can do
that well with an inductor in series and one in parallel.


Quote:

I have a new circuit that starts a 600 MHz coaxial ceramic resonator
colpitts oscillator at trigger time, and phase locks it to an OCXO
asap, still preserving the phase of the oscillator relative to the
trigger. It uses an ADC to digitize the phase difference, an FPGA to
do the math, and a DAC+varicap to tweak the CCRO. It also uses a dual
varicap per fig 1b in your paper. Driving the varicap junction is
interesting. I designed the loop and can barely understand it myself.

The TCXO thing I posted is interesting because it's delta-sigma in
space instead of the usual delta-sigma in time.



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
https://hobbs-eo.com

Les Cargill
Guest

Fri Jan 18, 2019 4:45 am   



John Larkin wrote:
Quote:
We were talking about TCXOs. One measures temperature and drives a
varicap through some nonlinear transfer function to get minumum net
TC.

We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise. I guess you could use a static
polynomial with the equivalent of nonvolatile DPOTS as the
coefficients.


This occurred to me, not as anything practical maybe but as an
interesting architecture.

https://www.dropbox.com/s/8ls632mndcxqby8/DAC_TCXO.JPG?raw=1

It's sort of a thermometer-code ADC, but each comparator incrementally
adds + or - one increment to the output.

As the temperature increases, we jog the output up or down one
increment at a time.

The sequence of switch settings become a delta-sigma code to make the
output.

The comparators could be sort of linear, not step outputs, to kind of
interpolate a bit. Some flash ADCs did something like that, soft
comparators.





Just use a regular DAC and an LPF and set the knee above a frequency
that matters. The output will mostly be zero, anyway.

It's temperature so it's already heavily integrated. You just don't want
too much process gain.

--
Les Cargill

Phil Hobbs
Guest

Fri Jan 18, 2019 2:45 pm   



On 1/17/19 10:13 PM, Les Cargill wrote:
Quote:
John Larkin wrote:
We were talking about TCXOs. One measures temperature and drives a
varicap through some nonlinear transfer function to get minumum net
TC.

We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise. I guess you could use a static
polynomial with the equivalent of nonvolatile DPOTS as the
coefficients.


This occurred to me, not as anything practical maybe but as an
interesting architecture.

https://www.dropbox.com/s/8ls632mndcxqby8/DAC_TCXO.JPG?raw=1

It's sort of a thermometer-code ADC, but each comparator incrementally
adds + or - one increment to the output.

As the temperature increases, we jog the output up or down one
increment at a time.

The sequence of switch settings become a delta-sigma code to make the
output.

The comparators could be sort of linear, not step outputs, to kind of
interpolate a bit. Some flash ADCs did something like that, soft
comparators.





Just use a regular DAC and an LPF and set the knee above a frequency
that matters. The output will mostly be zero, anyway.

It's temperature so it's already heavily integrated. You just don't want
too much process gain.


You can't usefully lowpass filter 1/f noise. It's really a different
regime, especially when you care about LF phase noise.

Some years ago I was building stabilized lasers for geophysical
applications (a downhole interferometric gravimeter). The basic idea is
that you can measure the density of rock by measuring gravity at the
surface (where the rock is pulling down) and then at depth, where some
of the rock is now pulling up. It was also intended for reservoir
management, where we'd leave one sensor at the bottom of the well and
correlate its data with that at the surface. (There are important
gravity variations due to barometric pressure, even.)

The laser had to have an Allan variance below 10**-10 at 100000 seconds
(about a day), so I locked a communications-type DFB laser to an
air-spaced etalon made from optically-contacted Zerodur, which was
itself temperature-controlled. (Optical contacting makes a hermetic
seal, which gets rid of the drift due to air density.)

The locking technique is one I invented almost 30 years ago: you sit
halfway up an interference fringe, subtract the photocurrents from the
transmitted and reflected beams, and servo at the null. That gets rid
of the AM noise contribution. You have to attenuate the reflected beam
a bit, because it's stronger than the transmitted beam due to cavity
losses. As long as you're super paranoid about fringes due to unwanted
surface reflections, it's a very very stable locking mechanism, and
doesn't require super-high finesse etalons like Pound-Drever-Hall.

Interestingly it turns out that if you adjust the attenuation so that

dR/d omega + dT/d omega = 0

at the same frequency where

R-T = 0

the out-of-band frequency noise decouples from the total amplitude
measurement as well, so theoretically you can do intracavity
measurements at the shot noise. (The loop suppresses the in-band noise.)

Filtering was not a useful concept.

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

Winfield Hill
Guest

Fri Jan 18, 2019 3:45 pm   



Phil Hobbs wrote...
Quote:

Some years ago I was building stabilized lasers for geophysical
applications (a downhole interferometric gravimeter). [snip]


Did you ever write that up?


--
Thanks,
- Win

Phil Hobbs
Guest

Fri Jan 18, 2019 4:45 pm   



On 1/18/19 9:31 AM, Winfield Hill wrote:
Quote:
Phil Hobbs wrote...

Some years ago I was building stabilized lasers for geophysical
applications (a downhole interferometric gravimeter). [snip]

Did you ever write that up?



Nah, I haven't published a paper since I left IBM. The technology
worked great, but the company went down the tubes (so to speak) when the
founder and main technical guy went off on the most spectacular midlife
crisis in my acquaintance--apparently he deserted his wife and five
children, then skipped off to China and shacked up with a 22-year-old
rich girl in Shanghai or someplace.

(February 22nd is the 10th anniversary of my consulting business--we're
going to throw a party.)

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

Les Cargill
Guest

Sat Jan 19, 2019 1:45 am   



Phil Hobbs wrote:
Quote:
On 1/17/19 10:13 PM, Les Cargill wrote:
John Larkin wrote:
We were talking about TCXOs. One measures temperature and drives a
varicap through some nonlinear transfer function to get minumum net
TC.

We don't want a digital design (ADC, lookup table or polynomial, DAC)
because that might add phase noise. I guess you could use a static
polynomial with the equivalent of nonvolatile DPOTS as the
coefficients.


This occurred to me, not as anything practical maybe but as an
interesting architecture.

https://www.dropbox.com/s/8ls632mndcxqby8/DAC_TCXO.JPG?raw=1

It's sort of a thermometer-code ADC, but each comparator incrementally
adds + or - one increment to the output.

As the temperature increases, we jog the output up or down one
increment at a time.

The sequence of switch settings become a delta-sigma code to make the
output.

The comparators could be sort of linear, not step outputs, to kind of
interpolate a bit. Some flash ADCs did something like that, soft
comparators.





Just use a regular DAC and an LPF and set the knee above a frequency
that matters. The output will mostly be zero, anyway.

It's temperature so it's already heavily integrated. You just don't
want too much process gain.

You can't usefully lowpass filter 1/f noise.


Wait, what? Is that a thing in TCXO's ? I meant the lowpass really as
just more integration - I do know you have to let these things get to
equilibrium before you can trust them.

Quote:
It's really a different
regime, especially when you care about LF phase noise.


Sounds like it then.


Quote:
Some years ago I was building stabilized lasers for geophysical
applications (a downhole interferometric gravimeter).  The basic idea is
that you can measure the density of rock by measuring gravity at the
surface (where the rock is pulling down) and then at depth, where some
of the rock is now pulling up.  It was also intended for reservoir
management, where we'd leave one sensor at the bottom of the well and
correlate its data with that at the surface.  (There are important
gravity variations due to barometric pressure, even.)

The laser had to have an Allan variance below 10**-10 at 100000 seconds
(about a day), so I locked a communications-type DFB laser to an
air-spaced etalon made from optically-contacted Zerodur, which was
itself temperature-controlled.  (Optical contacting makes a hermetic
seal, which gets rid of the drift due to air density.)

The locking technique is one I invented almost 30 years ago: you sit
halfway up an interference fringe, subtract the photocurrents from the
transmitted and reflected beams, and servo at the null.  That gets rid
of the AM noise contribution.  You have to attenuate the reflected beam
a bit, because it's stronger than the transmitted beam due to cavity
losses.  As long as you're super paranoid about fringes due to unwanted
surface reflections, it's a very very stable locking mechanism, and
doesn't require super-high finesse etalons like Pound-Drever-Hall.

Interestingly it turns out that if you adjust the attenuation so that

dR/d omega + dT/d omega = 0

at the same frequency where

R-T = 0

the out-of-band frequency noise decouples from the total amplitude
measurement as well, so theoretically you can do intracavity
measurements at the shot noise.  (The loop suppresses the in-band noise.)


That's crazy. Seems like it would also be a fine seismograph...

Quote:
Filtering was not a useful concept.


I would rather think not Smile I thought we were talking about a
temperature controller.

Quote:
Cheers

Phil Hobbs


--
Les Cargill

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