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From: Ban on 20 Feb 2010 02:17
Vladimir Vassilevsky wrote:
>
>> But how can you measure 1 PPM distortion? And where does it matter?
>
> State of the art geophysic instruments specmanship is ~130+ dB of SNR
> and ~120+ dB of THD (in the bandwidth of few hundred Hz). That's true
> numbers; we have them already. However I need to do a self test
> circuit that could confirm the performance numbers as well as a bunch
> of other parameters. It doesnt't have to be super accurate; it has to
> be simple. Board space is a premium, too.
>
>
> VLV

But that is a totally different piece of cake. Neither you need -120dB THD
nor 10uV accuracy nor 20bit DAC, you just need a stable passive attenuator
and reference.
ciao Ban


From: David L. Jones on 20 Feb 2010 03:46
Vladimir Vassilevsky wrote:
> Is there such DAC in the world, that would allow for:
>
> * pure THD ~ 0.0001%, SNR is not very critical.
> * frequency response up to several kHz
> * DC accuracy in 10mV range

Maybe:
http://www.cirrus.com/en/products/pro/detail/P1023.html

Their Geophysical parts are awesome (I've characterised them beyond their
datasheet specs):
http://www.cirrus.com/en/products/pro/detail/P1095.html
But not the bandwidth you want unfortunately.

Dave.

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---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
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From: David L. Jones on 20 Feb 2010 06:26
Phil Allison wrote:
> "Vladimir Vassilevsky = Ruskie TROLL "
>
>
>> State of the art geophysic instruments
>
> *** specmanship ***

Pretty much, welcome to the world of Geophysical measurement.
I spent more than decade in the industry, and I can assure you the
specmanship and brandmanship is real and *must* be met, otherwise you can
kiss your contracts bye-bye.

Analog Device are or were in the Geophysical sector too, but because Cirrus
Logic have the rep with the grey beard crowd, your products can also live or
die by which brand you choose.

I'm surprised Vladimir is asking about this stuff, as usually the decison is
already made for you :->
And I'm not sure why he needs several kHz bandwidth either, it's usually
several hundred Hz for this stuff.

Power consumption is the main killer in geophysical ADC/DAC systems, as you
have to typically power many thousands of channels over many km of cable.

Dave.
--
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.eevblog.com


From: Jon Kirwan on 20 Feb 2010 06:43
On Sat, 20 Feb 2010 22:26:39 +1100, "David L. Jones"
<altzone(a)gmail.com> wrote:

>Phil Allison wrote:
>> "Vladimir Vassilevsky = Ruskie TROLL "
>>
>>
>>> State of the art geophysic instruments
>>
>> *** specmanship ***
>
>Pretty much, welcome to the world of Geophysical measurement.
>I spent more than decade in the industry, and I can assure you the
>specmanship and brandmanship is real and *must* be met, otherwise you can
>kiss your contracts bye-bye.
>
>Analog Device are or were in the Geophysical sector too, but because Cirrus
>Logic have the rep with the grey beard crowd, your products can also live or
>die by which brand you choose.
>
>I'm surprised Vladimir is asking about this stuff, as usually the decison is
>already made for you :->

>And I'm not sure why he needs several kHz bandwidth either, it's usually
>several hundred Hz for this stuff.
><snip>

Vladimir wrote, "However I need to do a self test circuit
that could confirm the performance numbers as well as a bunch
of other parameters." I assumed the why of it is to be found
in some interpretation of "self test" and "confirm the
performance" parts. But you probably know how to "read" into
that a lot better than me.

Jon
From: John Larkin on 20 Feb 2010 10:48
On Sat, 20 Feb 2010 17:02:08 +1100, "Phil Allison" <phil_a(a)tpg.com.au>
wrote:

>
>"John Larkin"
>
>> But how can you measure 1 PPM distortion?
>
>** PC based audio measurement systems that use 24 bit sampling do it
>routinely.
>
> Just a matter of having a good FFT in software to resolve down to -130 dB.
>

That implies an ADC good to better than 1 PPM. Do they exist?

John

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