Re: 24 bit ADC testing
From: John Larkin (jjlarkin_at_highlandSNIPtechTHISnologyPLEASE.com)
Date: 07/17/04
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Date: Sat, 17 Jul 2004 10:58:07 -0700
On Fri, 16 Jul 2004 17:27:13 GMT, "colin"
<no.spam.for.me@ntlworld.com> wrote:
>
>"Bob Masta" <NoSpam@daqarta.com> wrote in message
>news:40f67c54.4837317@news.itd.umich.edu...
>> On 14 Jul 2004 06:48:50 -0700, sagarbirkar@gmail.com (sagar) wrote:
>>
>> >Hi,
>> > I need to check the performance of a 24 bit analog to digital
>> >converter.
>> >as in its main properties such as Integral Non Linearity,Differential
>> >Non Linearity etc without using an expensive setup.
>> >
>> > With
>> >regards,
>> > Sagar
>>
>> If the converter is part of a circuit that can send
>> data to a computer, you might be able to do this
>> by driving it with a very pure sine wave, taking
>> a large FFT (to get a low noise floor) and then
>> inferring the specs from the distortion spectrum.
>> I don't know off-hand how to convert a spectrum
>> into a discrete spec, but you can certainly use
>> this setup to grade parts or otherwise compare
>> units.
>>
>> Note that at this high bit-resolution, the surrounding
>> circuits, power supply, clocks, and what you ate for
>> breakfast are probably going to affect the results.
>>
>> Good luck with this, and please write back and let
>> us know how things work out!
>>
>>
>> Bob Masta
>> dqatechATdaqartaDOTcom
>>
>> D A Q A R T A
>> Data AcQuisition And Real-Time Analysis
>> www.daqarta.com
>
>
>depends how predictable the driving signal is, id probably try and use a
>ramp generator as id probably be more sure of being able to design and build
>a linear ramp generator easier than i wld a precise sinewave genarator.
>
It would be hard to build a ramp generator that's linear to 14 bits,
much less 24. Capacitors have dielectric absorption, c-vs-v effects,
and temperature drifts, and every semiconductor you use is full of
nonlinear capacitances. At 24 bits, every solder joint on the board is
a thermocouple, and every drift of air flails everything.
A ramp could give you some useful data on dnl, but delta-sigma ADCs
have inherently good dnl. Integral linearity is the test killer.
You can do some fun things by flipping over resistive voltage
dividers.
John
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