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mpm
Guest

Sat Jan 05, 2019 3:45 am   



On Thursday, December 27, 2018 at 6:45:35 AM UTC-5, Sylvia Else wrote:
Quote:
https://au.rs-online.com/web/p/crystal-oscillators/1485663/

$142.20

Is this the crystal oscillator equivalent of those absurdly expensive
speaker cables?

Sylvia.


I've given up trying to decipher vendor pricing.
For example, this relay
https://www.digikey.com/products/en?keywords=2961257
is $9.10

But you can get the whole DIN-rail carrier AND the relay for only $10.05
https://www.digikey.com/product-detail/en/phoenix-contact/2906223/277-12082-ND/5699610

And this wasn't really the example I was trying to find.
There's another model (same family) where it is much cheaper to purchase the DIN-rail version (complete with relay), than to buy the relay itself!!

Kevin Aylward
Guest

Sat Jan 05, 2019 9:45 am   



Quote:
wrote in message
news:9bb734a5-87b3-4c10-aebd-4ffd5a740222_at_googlegroups.com...

For the vast bulk of modern applications, sine waves are not required.
Standard precision xtal oscillators typically have cmos output, or what
is
referred to as "clipped sine". This latter is a misnomer though. In
practice,
its just a regulated slowish edged square wave. A key feature of the
regulated
output is
much better PS rejection to frequency.

The frequency content of a square wave is all the odd harmonics, with the
amplitude declining in proportion to harmonic number. Slow edges mean that
the higher >harmonics decline rather more rapidly, towards the triangular
wave case where the higher harmonics decline as the square of the harmonic
number.

If you fed the oscillator with a decent approximation to a sine wave in the
first place, the higher harmonic content is a lot lower.


Well, yeah, all the usual stuff, but not really of much note to precision
xtal oscillator applications.

Its all about stability of oscillator frequency verses temperature, supply
and load and phase noise.

Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

The limiter is always the dominant flatband noise source.

Quote:
I was a bit surprised when their AD797 blew the LT1028 away - it wasn't
any
quieter, but the output was a lot better behaved. I'd recommended it as
a
potential >alternative to the LT1028 to somebody who was having the
usual
troubles with the LT1028, and was surprised by the difference it seemed
to
make.

It has very good specs and is certainly an interesting topology. I can't
say
I understand why it would achieve a better specification than a two stage
at
this point in time. I will have to do a detailed apples for apples
comparison.

My feeling was that their - very elaborate - bipolar process gave then some
very high ft transistors and that they could minimise stray capacitances by
isolating them >better than the competition. That is the sort of impression
that an
Anaog Devices seminar is designed to create, so it isn't worth much.


I agree, the key to most really high performance designs, is not the so much
the design, as the process.

Quote:
I can't say I agree with the claim of "distortion cancelation" of the
output
stage. An amp with 110,000 loop gain at 1kH is going to have low
distortion,
period.

Off hand, if one had no Cc, there would be an almost standard Miller
compensation using Cn instead. Now... move Cn to the input of the unity
gain
output buffer.

I have previously done a lot of simulations on including and not
including
the output buffer with the comp capacitor and always get the same
distortion
for either condition.

But you aren't Bob Widlar or Barry Gilbert.


What's your point?

Quote:
The basic reason for this that for the comp cap on the
input to the buffer, the buffer is driven by a low impedance. This means
the
gain is comp cap linearized at the gain point B, fed into a fairly good
follower. If the comp cap is connected to the buffer output, the gain
stage
is now highly nonlinear because it is no longer feedback controlled by
the
comp cap. Additionally, its output impedance is high and all over the
place
so the follower is going to give large interactions with the gain stage,
causing gross distortion. The total amount of distortion reducing
feedback
gain is the same in either case.

Usually, there is no such thing as a free lunch. My bet is that in this
topology, simply moving that cap before and after the output buffer,
won't
make a difference to the distortion.

That probably isn't what is making the difference.


Its what they claim in their data sheet.

My take is that this topology's apparent success is down to having maybe,
10GHz+ Ft transistors.

It is very common for people to not understand how a topology really works
and attribute all sorts of nonsense to it.

A typically one is here:

http://www.kevinaylward.co.uk/ee/currentfeedbackmyth/currentfeedbackmyth.xht


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


Guest

Sat Jan 05, 2019 11:45 am   



On Saturday, January 5, 2019 at 7:11:25 PM UTC+11, Kevin Aylward wrote:
Quote:
wrote in message
news:9bb734a5-87b3-4c10-aebd-4ffd5a740222_at_googlegroups.com...


<snip>

Quote:
If you fed the oscillator with a decent approximation to a sine wave in the
first place, the higher harmonic content is a lot lower.

Well, yeah, all the usual stuff, but not really of much note to precision
xtal oscillator applications.


Since nobody seems to have tried it, it is still an open question.

Quote:
Its all about stability of oscillator frequency verses temperature, supply
and load and phase noise.


If you could be a bit pickier about how you sustained the oscillation, you might at least be able to take the supply sensitivity out of the game.

Quote:
Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.


Crystal oscillators tend to have remarkably high Q-values, so the sustaining current fed into them doesn't get the chance to generate much non-sinusoidal voltage across the crystal.

> The limiter is always the dominant flatband noise source.

But if you controlled the sustaining current more carefully you wouldn't need a limiter.

<snip>

Quote:
I have previously done a lot of simulations on including and not
including the output buffer with the comp capacitor and always get the same
distortion for either condition.

But you aren't Bob Widlar or Barry Gilbert.

What's your point?


They seem to have been able to come up with unexpected solutions.
There weren't many people in the area who could do that - I can't think of any others - but those two did exist.

Quote:
That probably isn't what is making the difference.

Its what they claim in their data sheet.


Data sheets do seem to be influenced by what the marketing people want to be said. They can't mess around with the performance claimed, but everything else seems to be open to spin.

Quote:
My take is that this topology's apparent success is down to having maybe,
10GHz+ Ft transistors.


Seems reasonable.

<snip>

--
Bill Sloman, Sydney

Kevin Aylward
Guest

Sat Jan 05, 2019 1:45 pm   



Quote:
wrote in message
news:689b2aba-5e80-40ad-945e-dc88a9ecad82_at_googlegroups.com...

If you fed the oscillator with a decent approximation to a sine wave in
the
first place, the higher harmonic content is a lot lower.

Well, yeah, all the usual stuff, but not really of much note to precision
xtal oscillator applications.


Since nobody seems to have tried it, it is still an open question.

Quote:
Its all about stability of oscillator frequency verses temperature,
supply
and load and phase noise.

If you could be a bit pickier about how you sustained the oscillation, you
might at least be able to take the supply sensitivity out of the game.


The supply sensitivity is taken out because I have a 100dB psrr on the
regulator. It is truly the easiest way to do it. 50 transistors in a
regulator, is nothing.

Its absolute impossible to design the oscillator itself with the required ps
rejection. The oscillator is optimised for noise. 10,000 transistor are used
to temp comp and linearize it. Its the ONLY way to do it in practice, at
high performance levels.


Quote:
Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.


Well, sure....

Quote:
The limiter is always the dominant flatband noise source.

But if you controlled the sustaining current more carefully you wouldn't
need a limiter.


This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output. The oscillator amplitude limiting to have the
gain equal to one is a different issue.

http://www.kevinaylward.co.uk/ee/phasenoise/phasenoise.html

Quote:
I have previously done a lot of simulations on including and not
including the output buffer with the comp capacitor and always get the
same
distortion for either condition.

But you aren't Bob Widlar or Barry Gilbert.

What's your point?

They seem to have been able to come up with unexpected solutions.
There weren't many people in the area who could do that - I can't think of
any others - but those two did exist.


...and your knowledge of my own professional career solutions to problems is
what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a flatband
noise level of 50nV/rthz

The BG regulator in my oscillators use 100uA (or less) to achieve that
noise.

Now, noise goes with the sqrt of the current. Using the Widlar et al
techniques would mean that, all things being equal, that my design should
result in (5/0.1)^2 = 2,500 times more noise. As far as I can see from
looking at the mainstream venders, none come remotely close to the
noise/current ratios achieved in my regulators.

The reality is, things have moved on. Many techniques the old guys used,
whilst very clever and appropriate at the time, have little relevance to
today. Way more sophisticated techniques are required.

The oscillators ASICs I design might target a total of only a few mA total
supply current, yet they still need < 50nV/sqrt noise performance for their
regulators. Legacy elementary designs just don't cut it. Today 10,000s of
transistor cost, essentially, nothing.

Today, its computers running 10,000 faster for simulations, with the
availability of 10,000s of transistors at < 1 cent cost. Producing "clever"
3rd order cheby response transfer function with 3 transistors, as Gilbert
indeed did, is just no longer the optimum way to design high precision
products.


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


Guest

Sat Jan 05, 2019 4:45 pm   



On Saturday, January 5, 2019 at 11:33:00 PM UTC+11, Kevin Aylward wrote:
Quote:
wrote in message
news:689b2aba-5e80-40ad-945e-dc88a9ecad82_at_googlegroups.com...

If you fed the oscillator with a decent approximation to a sine wave in
the first place, the higher harmonic content is a lot lower.

Well, yeah, all the usual stuff, but not really of much note to precision
xtal oscillator applications.

Since nobody seems to have tried it, it is still an open question.

Its all about stability of oscillator frequency verses temperature,
supply and load and phase noise.

If you could be a bit pickier about how you sustained the oscillation, you
might at least be able to take the supply sensitivity out of the game.

The supply sensitivity is taken out because I have a 100dB psrr on the
regulator. It is truly the easiest way to do it. 50 transistors in a
regulator, is nothing.


Bob Widlar did the same thing in his version of NE555 - the LM122 - albeit with a much slower timer. Sadly, it never sold well and is now obsolete.

Quote:
Its absolute impossible to design the oscillator itself with the required ps
rejection. The oscillator is optimised for noise. 10,000 transistor are used
to temp comp and linearize it. Its the ONLY way to do it in practice, at
high performance levels.


The only one that anybody has come up with so far.

Quote:
Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

But if you controlled the sustaining current more carefully you wouldn't
need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output.


The problem there is presumably the uncertainty of the position of the edges of the square wave - a comparator is just a fast amplifier, and amplifiers have input noise which make the edge detection happen earlier or later than it ideally should.

What you need is Percival distributed edge detector, where half a dozen separate comparators look at progressively delayed version of the same edge, and add the delayed outputs together after further complementary delays. Six of them would only give root six (2.45) reduction in the noise, but that might be worth having - if you have 10,000 transistors to play with, a little redundancy is permissible.

Similar things have been done in similar contexts.

Quote:
The oscillator amplitude limiting to have the
gain equal to one is a different issue.

http://www.kevinaylward.co.uk/ee/phasenoise/phasenoise.html


You seem to be confident that you are onto something, but don't seem to be able to find the words that make the idea intelligible.

Quote:
I have previously done a lot of simulations on including and not
including the output buffer with the comp capacitor and always get the
same
distortion for either condition.

But you aren't Bob Widlar or Barry Gilbert.

What's your point?

They seem to have been able to come up with unexpected solutions.
There weren't many people in the area who could do that - I can't think of
any others - but those two did exist.

..and your knowledge of my own professional career solutions to problems is
what?


You don't boast about the patents that name you as an inventor, for starters.

Bob Widlar and Barry Gilbert didn't have to - their names kept coming up in patent searches.

I spent a couple of years at EMI Central Research and got two patents out of it - places like than (and IBM) patented pretty much everything they could (even krw has got a couple patents out of his IBM time) but I did get exposed to people who were seriously creative.

<snipped stuff about current solutions being better than earlier ones, without any mention of where the recent good ideas had come from>

--
Bill Sloman, Sydney

Gerhard Hoffmann
Guest

Sat Jan 05, 2019 7:45 pm   



Am 05.01.19 um 13:32 schrieb Kevin Aylward:

Quote:

Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate
much non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.


No, if you can burn some power or do it not in a simplistic way.

Quote:

But if you controlled the sustaining current more carefully you
wouldn't need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output. The oscillator amplitude limiting to have the
gain equal to one is a different issue.


That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
< https://ieeexplore.ieee.org/document/494304 >

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)

<
https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf
>

And the LTC6957 family is also not bad.



Quote:
..and your knowledge of my own professional career solutions to problems
is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a
flatband noise level of 50nV/rthz


Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

A low noise voltage regulator is the LT3042/45, featuring 2 nV/rtHz.
(And finally, there is the negative Version also, LT3094)


Quote:
The BG regulator in my oscillators use 100uA (or less)  to achieve that
noise.


Just like the LT3042's reference current source.
The rest is only a follower.


Quote:
Now, noise goes with the sqrt of the current. Using the Widlar et al
techniques would mean that, all things being equal, that my design
should result in (5/0.1)^2 = 2,500 times more noise. As far as I can see
from looking at the mainstream venders, none come remotely close to the
noise/current ratios achieved in my regulators.


I have no doubt that Widlar could still point his index finger.

<
https://www.autodesk.com/products/eagle/blog/bob-widlar-life-engineering-legend/
>

Unfortunately, he has died nearly thirty years ago. Not exactly fair
to to target him for a comparison.

Quote:
The oscillators ASICs I design might target a total of only a few mA
total supply current, yet they still need < 50nV/sqrt noise performance
for their regulators. Legacy elementary designs just don't cut it. Today
10,000s of transistor cost, essentially, nothing.


regards,
Gerhard

Phil Hobbs
Guest

Sat Jan 05, 2019 11:45 pm   



On 1/5/19 1:17 PM, Gerhard Hoffmann wrote:
Quote:
Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate
much non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


But if you controlled the sustaining current more carefully you
wouldn't need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory.
to have a square wave output. The oscillator amplitude limiting to
have the gain equal to one is a different issue.

That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
    https://ieeexplore.ieee.org/document/494304   

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)


https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf
  

And the LTC6957 family is also not bad.



..and your knowledge of my own professional career solutions to
problems is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a
flatband noise level of 50nV/rthz

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.


Bandgaps are about 20 dB noisier than buried zeners, because they have
to multiply delta-Vbe by a factor of 10 and then add it to Vbe to get
the TCs to cancel.

Quote:

A low noise voltage regulator is the LT3042/45, featuring 2 nV/rtHz.
(And finally, there is the negative Version also, LT3094)


And of course if you have some reasonable load like 500 uA, a cap
multiplier with a low Rbb' transistor can get well under a nanovolt.

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


Guest

Sun Jan 06, 2019 2:45 am   



On Sunday, January 6, 2019 at 9:40:26 AM UTC+11, Phil Hobbs wrote:
Quote:
On 1/5/19 1:17 PM, Gerhard Hoffmann wrote:
Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate
much non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


But if you controlled the sustaining current more carefully you
wouldn't need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory.
to have a square wave output. The oscillator amplitude limiting to
have the gain equal to one is a different issue.

That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
    https://ieeexplore.ieee.org/document/494304   

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)


https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf
  

And the LTC6957 family is also not bad.

..and your knowledge of my own professional career solutions to
problems is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a
flatband noise level of 50nV/rthz

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

Bandgaps are about 20 dB noisier than buried zeners, because they have
to multiply delta-Vbe by a factor of 10 and then add it to Vbe to get
the TCs to cancel.


A low noise voltage regulator is the LT3042/45, featuring 2 nV/rtHz.
(And finally, there is the negative Version also, LT3094)

And of course if you have some reasonable load like 500 uA, a cap
multiplier with a low Rbb' transistor can get well under a nanovolt.


And there are also the Analog Devices XFET references

https://www.analog.com/en/analog-dialogue/articles/xfet-references.html

Their main advantage is that they can work at a lower supply voltage than is required for a buried zener.

https://www.analog.com/media/en/technical-documentation/data-sheets/ADR420_421_423_425.pdf

60nV per root Hz isn't impressive.

The National Bureau of Standards stacks up Josephson junctions, but that isn't a low power solution.

--
Bill Sloman, Sydney


Guest

Sun Jan 06, 2019 4:45 am   



On Sunday, January 6, 2019 at 5:17:28 AM UTC+11, Gerhard Hoffmann wrote:
Quote:
Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate
much non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


But if you controlled the sustaining current more carefully you
wouldn't need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output. The oscillator amplitude limiting to have the
gain equal to one is a different issue.

That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
https://ieeexplore.ieee.org/document/494304

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)


https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf


That does make sense. The result seems to be much the same as Kevin claims at

http://www.kevinaylward.co.uk/ee/phasenoise/FlickerNoiseNullification.xht

but the explanation is a whole lot more intelligible (for me at least).

<snip>

--
Bill Sloman, Sydney

Kevin Aylward
Guest

Sun Jan 06, 2019 2:45 pm   



Quote:
"Phil Hobbs" wrote in message
news:B-idnTtExYrPr6zBnZ2dnUU7-L3NnZ2d_at_supernews.com...


On 1/5/19 1:17 PM, Gerhard Hoffmann wrote:
Quote:
Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


But if you controlled the sustaining current more carefully you wouldn't
need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output. The oscillator amplitude limiting to have the
gain equal to one is a different issue.

That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
https://ieeexplore.ieee.org/document/494304

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)

https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf


And the LTC6957 family is also not bad.



..and your knowledge of my own professional career solutions to problems
is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a
flatband noise level of 50nV/rthz

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

Bandgaps are about 20 dB noisier than buried zeners, because they have to
multiply delta-Vbe by a factor of 10 and then add it to Vbe to get the TCs
to cancel.


Exactly.

I will say, that I did not invent the techniques that solve this x10 gain
problem, but in practice, implementing known techniques involves a lot more
than knowledge of just the basic ideas. What I am surprized though, is that
the likes of Analog Device are clearly not implementing known techniques to
achieve vastly superior performance.

and.... I am limited, as most are, to *standard* fab processes. Also, a 7V
zener aint going to cut it with a 2V7 min supply requirement.

The likes of Analog Devices have access to their own special processes.

Quote:

A low noise voltage regulator is the LT3042/45, featuring 2 nV/rtHz.
(And finally, there is the negative Version also, LT3094)

And of course if you have some reasonable load like 500 uA, a cap
multiplier with a low Rbb' transistor can get well under a nanovolt.


The problem is when you need low noise at 1Hz. A 1,000u cap is not
commercially viable for the products I am designing.

Filtering only works at higher frequency.

I am targeting the 1 Hz offset phase noise on a 10MHz oscillator at
something like -130dBc.

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

Kevin Aylward
Guest

Sun Jan 06, 2019 3:45 pm   



Quote:
wrote in message
news:c48dba3b-23d0-41d5-a19b-5aff21c7d598_at_googlegroups.com...

Its absolute impossible to design the oscillator itself with the required
ps
rejection. The oscillator is optimised for noise. 10,000 transistor are
used
to temp comp and linearize it. Its the ONLY way to do it in practice, at
high performance levels.

The only one that anybody has come up with so far.


Well.... I have been 10 years specifically designing oscillator ASICS, in a
company (Rakon) producing oscillators for 60 years, with a library stacked
with books on oscillator design. I have personally went through 100s of
topologies...

The issue with your comment, isn't that, sure, maybe there is a better
solution, but that it implies an unwarranted assumption that certain others
are too clueless to have come up with an optimum solution themselves.

As I said, it's *theoretically* impossible to design high stability
oscillators without regulating the ps, and its trivial to do the math to
prove this. "Captain, I cannie change the laws of physics, I need my 30
minutes."

We target 0.1ppb for a 5% ps change. If the current or voltage in an
oscillator changes, the frequency changes. Its that simple.

Quote:
Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

But if you controlled the sustaining current more carefully you wouldn't
need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output.

The problem there is presumably the uncertainty of the position of the
edges of the square wave - a comparator is just a fast amplifier, and
amplifiers have input noise >which make the edge detection happen earlier
or later than it ideally should.
What you need is Percival distributed edge detector, where half a dozen
separate comparators look at progressively delayed version of the same
edge, and add the >delayed outputs together after further complementary
delays. Six of them would only give root six (2.45) reduction in the noise,
but that might be worth having - if you >have 10,000 transistors to play
with, a little redundancy is permissible.


Interesting idea, but not realistic in an ASIC. Transmission line delay
lines probably is the only way to generate delay without adding excessive
noise. Active delay amplifiers are a complete non starter, explained below.

Modern design needs solutions that exist in semiconductor ascic.

>Similar things have been done in similar contexts.

The problem is the inherent noise of the comparator transistors.

The input comes from a highly band-limited xtal filtered output. It can be
shown that an ideal band limited input to an ideal comparator, has the same
So/No as the Si/Ni. See for example:

https://www.springer.com/gb/book/9781402076664

The issue though, is that it is impossible to band limit the internal noise
of the limiting amplifier. The net result is that the internal wideband
noise, generates around 12 dB more output phase noise than would be expected
from its amplitude noise. Its about power.

Every 1 mA might give about 1 Deg increase in temperature of an OCXO system.
A 5 deg increase might have the system running at 110 Deg instead of 105
Deg. Its a major problem for the xtal. A lot of systems have the xtal at,
maybe 90 Deg. The system loses regulation at its internal idle current
level.

Quote:
The oscillator amplitude limiting to have the
gain equal to one is a different issue.

http://www.kevinaylward.co.uk/ee/phasenoise/phasenoise.html

You seem to be confident that you are onto something, but don't seem to be
able to find the words that make the idea intelligible.


Oh... well those ideas have generated designs with 12dB lower noise than the
competition.

So, yeah... I am on to something...and... its not my problem that others
don't understand the theory.

Quote:
I have previously done a lot of simulations on including and not
including the output buffer with the comp capacitor and always get
the
same
distortion for either condition.

But you aren't Bob Widlar or Barry Gilbert.

What's your point?

They seem to have been able to come up with unexpected solutions.
There weren't many people in the area who could do that - I can't think
of
any others - but those two did exist.

..and your knowledge of my own professional career solutions to problems
is
what?

You don't boast about the patents that name you as an inventor, for
starters.


The best ideas are not always patented. Its called, keeping a secret.

Seriously, there is no way I can post either my BG regulators that beat
commercial BG regulators by orders of magnitude, or my oscillator designs,
similarly 12 dB superior in noise to the competition, because they are not
patentable. However, clearly few, if any, are using the specific structures
and operating conditions the way that I am using them.

Quote:
Bob Widlar and Barry Gilbert didn't have to - their names kept coming up in
patent searches.


I have seen many of their patents. Truly a waste of paper for most.

I already noted that Gilbert had a design for a 3rd order approximate
chebychev function, this was actually in a patent he had. No competent
designer is going to use that approach in a high performance TCXO/OCXO. I
just don't have the time to go into all the technical aspects of ASIC
design.

Usually, a patent is where the author is simply unaware of how others solve
the same problem in a standard topology.

Quote:
I spent a couple of years at EMI Central Research and got two patents out
of it - places like than (and IBM) patented pretty much everything they
could (even krw has >got a couple patents out of his IBM time) but I did
get exposed to people who were seriously creative.


The vast majority of patents are worthless. Big companies don't care how
much they lose in getting patents for obvious ideas. They are just sticks to
threaten people with.


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

Kevin Aylward
Guest

Sun Jan 06, 2019 3:45 pm   



Quote:
"Gerhard Hoffmann" wrote in message
news:g9caliF73srU1_at_mid.individual.net...

Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


Yes it is for the constraints that are pretty much universal in practical,
commercial product.

I won't go into the detail right now, but I can't afford more than a few mA
in the limiter.

e.g. 1 mA is around 1 Deg increase in temperature. A typically OCXO might
have its xtal at 92 Deg.

You can't regulate the heater below the operating power of the ASIC. The
output buffers can use 5 mA for starters.

Quote:
..and your knowledge of my own professional career solutions to problems
is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a flatband
noise level of 50nV/rthz

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

A low noise voltage regulator is the LT3042/45, featuring 2 nV/rtHz.
(And finally, there is the negative Version also, LT3094)


And don't make me laugh :-)

Been there, just haven't wrote the book....

That device has 70nV/rthz at 10 Hz. It relies on a big honking capacitor of
4u7 to achieve that. With 0.47uf, its 300nV/rthz
Its probably about 700 uV/rthz at 1Hz, truly dreadful , and unusable for my
applications.

Its regulator current is extremely noisy. It just filters it. Its raw,
unfiltered value looks like around 5 uV/rthz at 1 Hz.

I am looking for 100nV/rt hz at 1Hz, with only a few 0.1uf capacitors in the
oscillator package, which might be 5mm X 7mm

My BG get 50nV at that low current, with no capacitor. It uses a couple of
ext caps in order to get its 80dB PSR at 1 MHz.

Look. I have literally, investigated 100s of BG topologies, over several
calendar years, and 100,000s of simulations. I am a leading expert in BG
design. It's a fact. Take that as you will.


Quote:
The BG regulator in my oscillators use 100uA (or less) to achieve that
noise.

Just like the LT3042's reference current source.
The rest is only a follower.


See above, the *BG* in the LT3042 is shit for noise.


Quote:
Now, noise goes with the sqrt of the current. Using the Widlar et al
techniques would mean that, all things being equal, that my design should
result in (5/0.1)^2 = 2,500 times more noise. As far as I can see from
looking at the mainstream venders, none come remotely close to the
noise/current ratios achieved in my regulators.

I have no doubt that Widlar could still point his index finger.


In the real would, there are many, many people very skilled in what they do.
Most don't write books or application notes.

The idea that some few golden oldies are the only experts is both arrogant
and naive.

<
https://www.autodesk.com/products/eagle/blog/bob-widlar-life-engineering-legend/
Quote:


Unfortunately, he has died nearly thirty years ago. Not exactly fair to to
target him for a comparison.


Widlar was a very, very impressive guy. The point I am making is that it is
just a fact, that the design techniques he used then, have limited utility
today.

He did what was optimum then. Today, we have vastly better processes,
immense computer power,and the cost of 10,000 transistors, even at analogue
sizes < 1 cent.

What took him 170 hours of continuous experimentation, I can set up in
Cadence to do, and run in a few minutes.

The fact that Widlar *might* do vastly better designs today, with new tools,
is not relevant to the fact that I am doing designs, today, vastly superior
to what he ever achieved. I get paid for what I achieve today, not whether a
dead person, may or may not achieve if he were alive.

What I will say, is that the mind set that I have is correct for todays
technology. I understand that there is usually, zero value in designing a
circuit with 3 transistors, rather than 50, if the 50 transistor circuit is
either quicker to design, more reliable, easier to design, easier to
validate or has higher performance etc.

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

John Larkin
Guest

Sun Jan 06, 2019 6:45 pm   



On Sun, 6 Jan 2019 14:05:15 -0000, "Kevin Aylward"
<kevinRemovAT_at_kevinaylward.co.uk> wrote:

Quote:

The vast majority of patents are worthless. Big companies don't care how
much they lose in getting patents for obvious ideas. They are just sticks to
threaten people with.


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


One dumb thing that a lot of startups do is spend a fortune getting a
lot of silly patents. Well, maybe not totally dumb, because it does
impress some investors. But it soaks up the energy of the innovators,
not to mention a heap of money.

We just keep things private and invent new stuff faster than the
competition can reverse engineer the existing stuff.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

John Larkin
Guest

Sun Jan 06, 2019 6:45 pm   



On Sun, 6 Jan 2019 13:36:24 -0000, "Kevin Aylward"
<kevinRemovAT_at_kevinaylward.co.uk> wrote:

Quote:
"Phil Hobbs" wrote in message
news:B-idnTtExYrPr6zBnZ2dnUU7-L3NnZ2d_at_supernews.com...

On 1/5/19 1:17 PM, Gerhard Hoffmann wrote:
Am 05.01.19 um 13:32 schrieb Kevin Aylward:


Many applications like quite a tight 50:50 duty cycle though. xtal
oscillators automatically give not a bad sine wave to drive the
limiter/squarer.

Crystal oscillators tend to have remarkably high Q-values, so the
sustaining current fed into them doesn't get the chance to generate much
non-sinusoidal voltage >across the crystal.

Well, sure....

The limiter is always the dominant flatband noise source.

No, if you can burn some power or do it not in a simplistic way.


But if you controlled the sustaining current more carefully you wouldn't
need a limiter.

This is not the limiting of the oscillator, it is the squaring up
*comparator* that converts the sine wave to rectangle. Its mandatory. to
have a square wave output. The oscillator amplitude limiting to have the
gain equal to one is a different issue.

That is not exactly big news.

Oliver Collins: The design of low jitter hard limiters
https://ieeexplore.ieee.org/document/494304

(I have seen it outside of the IEEE Wall Of Shame in the wilderness
of the internet.)

https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2018_comparator_noise.pdf


And the LTC6957 family is also not bad.



..and your knowledge of my own professional career solutions to problems
is what?

What I can say, as an example...

Lets take the absolute best low noise (BG) regulator from Analog devices.

For example the LTC6655. It needs 5mA standby current. It shows a
flatband noise level of 50nV/rthz

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

Bandgaps are about 20 dB noisier than buried zeners, because they have to
multiply delta-Vbe by a factor of 10 and then add it to Vbe to get the TCs
to cancel.

Exactly.

I will say, that I did not invent the techniques that solve this x10 gain
problem, but in practice, implementing known techniques involves a lot more
than knowledge of just the basic ideas. What I am surprized though, is that
the likes of Analog Device are clearly not implementing known techniques to
achieve vastly superior performance.

and.... I am limited, as most are, to *standard* fab processes. Also, a 7V
zener aint going to cut it with a 2V7 min supply requirement.

The likes of Analog Devices have access to their own special processes.


They have a jfet bandgap-sort-of reference that's awfully good.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Kevin Aylward
Guest

Sun Jan 06, 2019 7:45 pm   



"John Larkin" wrote in message
news:7hc43eduresdqk0t7rvvptofbig6f4ijdk_at_4ax.com...

Quote:

Don't make me laugh so hard. The LT6655 is a bandgap reference that is
quite good as far as bandgaps go noisewise. 50 nV/rtHz is about a
careless implemented LM317.

Bandgaps are about 20 dB noisier than buried zeners, because they have to
multiply delta-Vbe by a factor of 10 and then add it to Vbe to get the TCs
to cancel.

Exactly.

I will say, that I did not invent the techniques that solve this x10 gain
problem, but in practice, implementing known techniques involves a lot more
than knowledge of just the basic ideas. What I am surprized though, is that
the likes of Analog Device are clearly not implementing known techniques to
achieve vastly superior performance.

and.... I am limited, as most are, to *standard* fab processes. Also, a 7V
zener aint going to cut it with a 2V7 min supply requirement.

The likes of Analog Devices have access to their own special processes.

They have a jfet bandgap-sort-of reference that's awfully good.


I have seen that one. Its impressive.

Its why I stated BG (sum of dVbe and Vbe). I am aware of some of the other
techniques that take advantage of special processes.

I am stuck to a commercial BiCMOS process. I chose a good one, but it still
has limitations. It would be great to have SiCr resistors from another
process.


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

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