Re: [time-nuts] DAC performance

2017-07-17 Thread Richard (Rick) Karlquist 



On 7/17/2017 1:41 PM, Attila Kinali wrote:

On Mon, 17 Jul 2017 12:07:29 -0700
"Richard (Rick) Karlquist"  wrote:


On 7/17/2017 10:54 AM, Azelio Boriani wrote:

This implies that in a Rb or Cs there is not a voltage reference source?



Yes, that's right, there is no voltage reference with a material
effect on stability or accuracy.


How about the temperature and C-field control? Aren't those based
on keeping the output of a sensor stable compared to a voltage reference?

Attila Kinali



Good oven design is typically done with thermistor/resistor bridges 
which are ratiometric and definitely don't depend on a reference.

In the 5071A, the C field is controlled with
a Zeeman splitting check, hence no reference involved.  In
older Cs standards, the C field accuracy depended on a reference
but it didn't require a very good one to get sufficient accuracy
in the C field.  In Rb standards, the C field is so crude it
is often adjusted using a pot.

Rick N6RK
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Re: [time-nuts] DAC performance

2017-07-17 Thread Charles Steinmetz 

Attila wrote:


Charles Steinmetz  wrote:



how about the LTC1650?
 * * *
[it] is nearly 100x (40dB) quieter (30nV/sqrtHz vs. 280) [than the 1650]



I was about to ask the same question :-)


Note:  I divided 280 by 30 and got "nearly 100x".   D'Oh!  Of course, it 
is ~10x, or 20dB, not ~100x or 40dB as I stated.  Still, a ~20dB noise 
advantage is substantial.


One point I didn't mention previously -- the 1650 is only marginally 
more expensive than the 1655.



I am sure there are ways to compensate for the charge injection
by using multiple switches, but I have not been able to come up
with a good way. Does anyone have a good idea?


I've tried several approaches to cancel the glitch energy of analog 
switches, but I never hit on anything I was really happy with -- partly 
because the glitch energy is more random than you'd like and partly 
because the "kludge factor" of multiple-switch solutions exceeds my 
tolerance pretty quickly.  Even if you accept the high kludge factor, 
you find that like input bias current cancellation, glitch cancellation 
is most effective (only really effective??) if it is done on-chip.


Best regards,

Charles


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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-17 Thread Attila Kinali 
On Sun, 16 Jul 2017 14:24:24 -0400
Charles Steinmetz  wrote:


> Well, to name just the first one that comes to mind, how about the 
> LTC1650?  Like the 1655, it is available in SO and DIP packages.  Its 
> differential nonlinearity is >2x better than the 1655, it settles 5x 
> faster (4uS vs. 20uS to 1 LSB) and is nearly 100x (40dB) quieter 
> (30nV/sqrtHz vs. 280).  The 1650 has substantially lower glitch energy, 
> as well (1.8nV-S for the 1650, 12nV-S for the 1655).

I was about to ask the same question :-)

BTW: I am planning to do something similar with an LT1650 and
thought about adding an CMOS switch to minimize the glitch energy.
Though even low charge injection switches like the ADG5212/5213
give something in the order of 0.5pC.. which turns out to be in the
order of magnitude of the LTC1650's worst case glitch energy, if put
into a complete circuit.

I am sure there are ways to compensate for the charge injection
by using multiple switches, but I have not been able to come up
with a good way. Does anyone have a good idea?

> I have not surveyed the field to see what other "SO or easier to solder" 
> DACs are available with better performance than the 1655, but I'm sure 
> there are others.

There is also the AD5060 family from Analog. Though their performance
is slightly worse then the LTC1650, they are much cheaper. Unless you
need the high specs, they are a cheap alternative.
 
Attila Kinali

-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] DAC performance

2017-07-17 Thread Attila Kinali 
On Mon, 17 Jul 2017 12:07:29 -0700
"Richard (Rick) Karlquist"  wrote:

> On 7/17/2017 10:54 AM, Azelio Boriani wrote:
> > This implies that in a Rb or Cs there is not a voltage reference source?
> > 
> 
> Yes, that's right, there is no voltage reference with a material
> effect on stability or accuracy.

How about the temperature and C-field control? Aren't those based
on keeping the output of a sensor stable compared to a voltage reference?

Attila Kinali

-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-17 Thread Richard (Rick) Karlquist 



On 7/17/2017 10:54 AM, Azelio Boriani wrote:

This implies that in a Rb or Cs there is not a voltage reference source?



Yes, that's right, there is no voltage reference with a material
effect on stability or accuracy.

Rick N6RK
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-17 Thread Azelio Boriani 
This implies that in a Rb or Cs there is not a voltage reference source?

On Mon, Jul 17, 2017 at 3:49 AM, Bob kb8tq  wrote:
> HI
>
> This is a limitation on an OCXO based GPSDO. That’s really the bottom line 
> here.
> It’s a limitation in an OCXO based part, but not in one based on an Rb or a 
> Cs. If
> the added component costs far more than a Cs, it’s not an answer.
>
> Bob
>
>> On Jul 16, 2017, at 7:25 PM, Chris Albertson  
>> wrote:
>>
>> What about josephson standards?   After all, this is "Time Nuts" and we are
>> allowed to propose silly-complex solutions to simple problems if it
>> improves performance even a little.
>>
>> But seriously I thought the issue of making a perfect voltage standard was
>> solved because the Volt is defined to be whatever the Josephson array
>> produces. Yes expensive because to runs at nearly absolute zero.
>>
>> On Sun, Jul 16, 2017 at 4:10 PM, Bob kb8tq  wrote:
>>
>>> Hi
>>>
 On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist <
>>> rich...@karlquist.com> wrote:



 On 7/16/2017 1:51 PM, Bob kb8tq wrote:
> Hi
> One gotcha with any ADC or DAC is going to be the reference. There, you
>>> are in the same
> “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not
>>> very stable, can do.
> Both stable and quiet, not so easy if you want it cheap.
> Noise can also be the sigma delta ADC’s weak point. Even at slow rates,
>>> some of them need
> a lot of averages to quiet down.

 The reference initially used in the E1938A turned out to be too
>>> noisy/unstable.  It was non trivial to find an upgrade.  The
 HP Smart Clocks of 20 years ago were limited in their performance
 by the reference used.

 Has there been much improvement in references in the intervening
 20 years?
>>>
>>> They still don’t seem to have the hysteresis problem licked. Yes, you can
>>> do an oversized reference
>>> and take care of the issue. More or less that’s what you would have done
>>> 20 years ago.
>>>
>>> Bob
>>>
>>>

 Rick N6RK
>>>
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>>> mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>>
>>
>>
>> --
>>
>> Chris Albertson
>> Redondo Beach, California
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>
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Bob kb8tq 
HI

This is a limitation on an OCXO based GPSDO. That’s really the bottom line 
here. 
It’s a limitation in an OCXO based part, but not in one based on an Rb or a Cs. 
If
the added component costs far more than a Cs, it’s not an answer. 

Bob

> On Jul 16, 2017, at 7:25 PM, Chris Albertson  
> wrote:
> 
> What about josephson standards?   After all, this is "Time Nuts" and we are
> allowed to propose silly-complex solutions to simple problems if it
> improves performance even a little.
> 
> But seriously I thought the issue of making a perfect voltage standard was
> solved because the Volt is defined to be whatever the Josephson array
> produces. Yes expensive because to runs at nearly absolute zero.
> 
> On Sun, Jul 16, 2017 at 4:10 PM, Bob kb8tq  wrote:
> 
>> Hi
>> 
>>> On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist <
>> rich...@karlquist.com> wrote:
>>> 
>>> 
>>> 
>>> On 7/16/2017 1:51 PM, Bob kb8tq wrote:
 Hi
 One gotcha with any ADC or DAC is going to be the reference. There, you
>> are in the same
 “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not
>> very stable, can do.
 Both stable and quiet, not so easy if you want it cheap.
 Noise can also be the sigma delta ADC’s weak point. Even at slow rates,
>> some of them need
 a lot of averages to quiet down.
>>> 
>>> The reference initially used in the E1938A turned out to be too
>> noisy/unstable.  It was non trivial to find an upgrade.  The
>>> HP Smart Clocks of 20 years ago were limited in their performance
>>> by the reference used.
>>> 
>>> Has there been much improvement in references in the intervening
>>> 20 years?
>> 
>> They still don’t seem to have the hysteresis problem licked. Yes, you can
>> do an oversized reference
>> and take care of the issue. More or less that’s what you would have done
>> 20 years ago.
>> 
>> Bob
>> 
>> 
>>> 
>>> Rick N6RK
>> 
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Chris Albertson 
What about josephson standards?   After all, this is "Time Nuts" and we are
allowed to propose silly-complex solutions to simple problems if it
improves performance even a little.

But seriously I thought the issue of making a perfect voltage standard was
solved because the Volt is defined to be whatever the Josephson array
produces. Yes expensive because to runs at nearly absolute zero.

On Sun, Jul 16, 2017 at 4:10 PM, Bob kb8tq  wrote:

> Hi
>
> > On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist <
> rich...@karlquist.com> wrote:
> >
> >
> >
> > On 7/16/2017 1:51 PM, Bob kb8tq wrote:
> >> Hi
> >> One gotcha with any ADC or DAC is going to be the reference. There, you
> are in the same
> >> “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not
> very stable, can do.
> >> Both stable and quiet, not so easy if you want it cheap.
> >> Noise can also be the sigma delta ADC’s weak point. Even at slow rates,
> some of them need
> >> a lot of averages to quiet down.
> >
> > The reference initially used in the E1938A turned out to be too
> noisy/unstable.  It was non trivial to find an upgrade.  The
> > HP Smart Clocks of 20 years ago were limited in their performance
> > by the reference used.
> >
> > Has there been much improvement in references in the intervening
> > 20 years?
>
> They still don’t seem to have the hysteresis problem licked. Yes, you can
> do an oversized reference
> and take care of the issue. More or less that’s what you would have done
> 20 years ago.
>
> Bob
>
>
> >
> > Rick N6RK
>
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> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Bob kb8tq 
Hi

> On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
> On 7/16/2017 1:51 PM, Bob kb8tq wrote:
>> Hi
>> One gotcha with any ADC or DAC is going to be the reference. There, you are 
>> in the same
>> “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not very 
>> stable, can do.
>> Both stable and quiet, not so easy if you want it cheap.
>> Noise can also be the sigma delta ADC’s weak point. Even at slow rates, some 
>> of them need
>> a lot of averages to quiet down.
> 
> The reference initially used in the E1938A turned out to be too 
> noisy/unstable.  It was non trivial to find an upgrade.  The
> HP Smart Clocks of 20 years ago were limited in their performance
> by the reference used.
> 
> Has there been much improvement in references in the intervening
> 20 years?

They still don’t seem to have the hysteresis problem licked. Yes, you can do an 
oversized reference
and take care of the issue. More or less that’s what you would have done 20 
years ago.

Bob


> 
> Rick N6RK

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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Richard (Rick) Karlquist 



On 7/16/2017 1:51 PM, Bob kb8tq wrote:

Hi

One gotcha with any ADC or DAC is going to be the reference. There, you are in 
the same
“get what you pay for” dilemma. Stable and noisy, can do. Quiet and not very 
stable, can do.
Both stable and quiet, not so easy if you want it cheap.

Noise can also be the sigma delta ADC’s weak point. Even at slow rates, some of 
them need
a lot of averages to quiet down.



The reference initially used in the E1938A turned out to be too 
noisy/unstable.  It was non trivial to find an upgrade.  The

HP Smart Clocks of 20 years ago were limited in their performance
by the reference used.

Has there been much improvement in references in the intervening
20 years?

Rick N6RK
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Bob kb8tq 
Hi

One gotcha with any ADC or DAC is going to be the reference. There, you are in 
the same 
“get what you pay for” dilemma. Stable and noisy, can do. Quiet and not very 
stable, can do. 
Both stable and quiet, not so easy if you want it cheap. 

Noise can also be the sigma delta ADC’s weak point. Even at slow rates, some of 
them need
a lot of averages to quiet down. 

Does this or that design need this or that level of stability or noise? That 
depends a lot on the 
approach used. In a GPSDO, cutting down on the EFC range is a great way to 
“cost reduce” the 
rest of the circuit in terms of noise and stability.  Well made modern OCXO’s 
don’t drift a lot ….

Bob

> On Jul 16, 2017, at 2:24 PM, Charles Steinmetz  wrote:
> 
> Bert wrote:
> 
>> We limited to affordable  and solderable.
>> The LTC1655 was the clear winner because
>> of linearity and temperature
>>  * * *
>> Five years later I know no better alternative
> 
> Well, to name just the first one that comes to mind, how about the LTC1650?  
> Like the 1655, it is available in SO and DIP packages.  Its differential 
> nonlinearity is >2x better than the 1655, it settles 5x faster (4uS vs. 20uS 
> to 1 LSB) and is nearly 100x (40dB) quieter (30nV/sqrtHz vs. 280).  The 1650 
> has substantially lower glitch energy, as well (1.8nV-S for the 1650, 12nV-S 
> for the 1655).
> 
> Not all of the better specs are required for steering an oscillator at GPSDO 
> rates, but others are a distinct advantage.
> 
> I have not surveyed the field to see what other "SO or easier to solder" DACs 
> are available with better performance than the 1655, but I'm sure there are 
> others.
> 
> This is to take nothing away from the 1655 -- I have accounted for thousands 
> of them in my own designs, and think very highly of it.
> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

2017-07-16 Thread Charles Steinmetz 

Bert wrote:


 We limited to affordable  and solderable.
 The LTC1655 was the clear winner because
 of linearity and temperature
  * * *
 Five years later I know no better alternative


Well, to name just the first one that comes to mind, how about the 
LTC1650?  Like the 1655, it is available in SO and DIP packages.  Its 
differential nonlinearity is >2x better than the 1655, it settles 5x 
faster (4uS vs. 20uS to 1 LSB) and is nearly 100x (40dB) quieter 
(30nV/sqrtHz vs. 280).  The 1650 has substantially lower glitch energy, 
as well (1.8nV-S for the 1650, 12nV-S for the 1655).


Not all of the better specs are required for steering an oscillator at 
GPSDO rates, but others are a distinct advantage.


I have not surveyed the field to see what other "SO or easier to solder" 
DACs are available with better performance than the 1655, but I'm sure 
there are others.


This is to take nothing away from the 1655 -- I have accounted for 
thousands of them in my own designs, and think very highly of it.


Best regards,

Charles


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