[time-nuts] Next upgrade

Attila Kinali attila at kinali.ch
Sun Nov 26 08:26:55 EST 2017

On Thu, 23 Nov 2017 13:18:35 -0500
Bert Kehren via time-nuts <time-nuts at febo.com> wrote:

> There was recently discussion of the use of the LTC1655 which 
> is still my # 1  choice. What was not mentioned on the 1650 is that in needs 
> a external reference  discontinued and double ling the cost.

There is just a tad bit of catch here:
The LTC1655 has an order of magnitude higher noise, a factor 2-3 higher
tempco of an LTC1650+LTC6655, a factor 2 higher DNL and a factor 2 higher INL.
The LTC1650 is the better DAC. That's why it's more expensive.

Whether the increased performance is worth the money or not, depends
on the application.

While we are at it, I'd like to mention the LTC1821. It beats the LTC1650
in most parameters, including price. But it has an increadibly low
spec'ed noise (typ 20nV/sqrt(Hz) at full scale output)

> 18 bits would be nicer but we have not  found one affordable.

It seems that manufacturing gets too costly for anything beyond 16bit
(unless you cut off at 10Hz).

Though, if you have a decent 16bit DAC and want to get to 18bit,
that's fairly simple using delta-sigma modulation... if you can live
with a low pass fillter after the DAC. But the DNL will be the limiting
factor here (unless you use some special techniques) and the (absolute) INL
will not get better, for obvious reasons.

			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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