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Re: dac architecture
On 05/01/2019 17:55, John Larkin wrote:
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Couldn't you do it all digitally and then low pass filter the output so  
that the phase noise is kept within acceptable bounds. Sounds like you  
will need to calibrate every one against a good reference oscillator.

--  
Regards,
Martin Brown

Re: dac architecture
On Sun, 6 Jan 2019 10:26:04 +0000, Martin Brown

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Any good TCXO will need to be temperature swept and calibrated. You
can trim resistors in a thermistor network, trim polynomial terms,
load a ROM lookup table, or flip my row of switches. The cal has to be
nonvolatile somehow.

Most small TCXOs have a couple of DNC pins which I assume are an
SPI-like programming port.

"NC" sometimes means "not connected internally" and sometimes means
"do not connect to this pin."


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dac architecture
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Maybe you could use a standard xtal TCXO asic and use it just for its  
inbuilt nonvolatile DPOTS driving its polynomial compensation?

Its a standard problem, already solved for 20+ years.

We (Rakon) don't source our own asics to external customers, but AKM does

https://www.akm.com/akm/en/product/detail/0041/

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: dac architecture
On Sun, 6 Jan 2019 18:53:39 -0000, "Kevin Aylward"

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Sure, you can always buy a chip and an eval board and not design
anything and be done. But then, all your competition can too, so it
becomes a race to the bottom on volume and cost.

I just thought this architecture, delta-sigma in bit-set space, was
interesting.  

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No public data sheet, apparently. How does that one work?  


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dac architecture
John Larkin wrote:

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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

Re: dac architecture
On Mon, 7 Jan 2019 21:25:49 +0100, Piotr Wyderski

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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  

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Re: dac architecture
John Larkin wrote:

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Now it makes sense, thanks!

    Best regards, Piotr

Re: dac architecture
John Larkin wrote:
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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

Re: dac architecture
On 1/17/19 10:13 PM, Les Cargill wrote:
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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
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Re: dac architecture
Phil Hobbs wrote...
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 Did you ever write that up?


--  
 Thanks,
    - Win

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

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Sounds like it then.


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

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

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--  
Les Cargill


Re: dac architecture

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You mentioned in a response to the above that you had not published anything  
since your IBM tenure.

But did you describe this method in "Building Electro-Optical Systems: Making  
it all Work"?

Joe Gwinn


Re: dac architecture
On 1/19/19 12:46 PM, Joseph Gwinn wrote:
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No, but it's in an old patent:
<https://electrooptical.net/static/eoi/patents/US06259712__.pdf .

I'll probably put it in the third edition--it's a great trick.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: dac architecture
Phil Hobbs wrote...
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 Do you have any other goodies like that, which you
 have only published as a patent?


--  
 Thanks,
    - Win

Re: dac architecture
On 1/19/19 2:00 PM, Winfield Hill wrote:
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Well, it depends what you're interested in.  There's a patent on  
total-metal detection in process water, which was really fun:

https://electrooptical.net/static/eoi/patents/US06259712__.pdf

and of course the rest are at

https://electrooptical.net/Patents/

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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