Re: [time-nuts] Papers on timing for lunar laser ranging
On Sun, 16 Jul 2017 14:24:24 -0400
Charles Steinmetz csteinmetz@yandex.com 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
Attila wrote:
Charles Steinmetz csteinmetz@yandex.com 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
On 7/17/2017 1:41 PM, Attila Kinali wrote:
On Mon, 17 Jul 2017 12:07:29 -0700
"Richard (Rick) Karlquist" richard@karlquist.com 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