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Arbitrary waveform generator with auto-calibration

Hi all,

I'm designing an arbitrary wavefrom generator. The requirments are : 100MSPS, +-10V or 0-10V You can see my schematics here

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These are my plan auto-calibration; FPGA gives a value to the DAC, then with a feedback path to an ADC the FPGA reads back the analog output. After comparison between the 2 values a corrections will be done numerically inside the FPGA.

As I'm a begginer in this application field, I'd like to know if it is a sensible way to do. If somebody have already done some kind of DAC auto-calibration, all advices and critical to my schematics are welcome.

Thanks Matthieu

Reply to
Matthieu Cattin
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Perhaps this is a stupid question, but is the ADC in fact more accurate than the DAC?

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John Devereux
Reply to
John Devereux

Why not use a precision voltage source for the DAC? An accuracy below

1% should be feasible. 
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Reply to
Nico Coesel

Reply to
Matthieu Cattin

Reply to
Matthieu Cattin

What is your spec?, can you make your output stage with precision components and live with a small amount of error? 0.01% precision can be had for a price.

Dave :)

Reply to
David L. Jones

But I how do you manage DAC errors ?

Reply to
Matthieu Cattin

If you want to match your ADC/DAC pair for range then gain error will be your main problem. In which case try and use the same reference for both ADC and DAC (if possible).

Offset error in the DAC will be around the same as your output circuitry.

Remember you are only running just over 10 effective bits with your

14bit converter, so don't get too hung up on the errors.

Dave :)

Reply to
David L. Jones

You have there a 14-bit D/A, with built-in self-calibration, so you must be wanting to reduce the errors in the following analog stages.

And there you have a HECK of a problem. I don't know of any op-amps capable of 100MHz bandwidth and gain-flat to one part in 16,384 !! Even with those hi-falootin THS3091's, they only settle to .1% in 40ns.

So you have a bit of a mismatch there-- the D/A has over ( 16 * 4 ) squared times the accuracy of your following stages. ANnd maybe square that again if you include a feedback path. And no amount of digital feedback is going to help these transient errors-- the horse has already left the barn.

Maybe you better tell us exactly what kind of frequency response and accuracy you really need.

Right now you're very far away from being able to use all the capabilities of that D/A.

Regards,

A_H

Reply to
Ancient_Hacker

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