[sdiy] How to measure 1-bit DAC performance?

[Tom Wiltshire]

Hi Roman,

I doubt the multimeter measures much better than 1% accurate, in which case, I might distinguish 7-bit outputs, but I won't be able to reliably measure 10-bit, and if the NCO gives a better output (say, 12-bit) I don't stand a chance.

Is there something I'm missing? Can I overcome this limitation?

Thanks,
Tom

On 25 Apr 2017, at 14:38, Roman Sowa <modular at go2.pl> wrote:

> Measure DC and AC specs like with any other DACs.
> For example write a little program in the PIC that outputs every code in the range, or limit that to reasonable number of levels like 1024 and measure actual voltage with multimeter. Good if your multimeter can log data.
> When you export multimeter data to spreadsheet, you can do all calculations and what's more fun - graphs, to see DAC performance clearly, especially INL.
> 
> For AC specs, make your PIC generate a sine and record the output with your computer running ARTA software or anything similar. A very slow wave could also help determining noise at various DC levels, because as PWM, it may whistle.
> 
> From that you will get Effective Number of Bits which is what you're after I think.
> 
> Roman
> 
> W dniu 2017-04-25 o 15:09, Tom Wiltshire pisze:
>> Hi All,
>> 
>> I've been using the PWM output module on the PIC chips as a cheap DAC for years. It does this job reasonably well, all things considered. Whilst the quality and 10-bit resolution aren't great, it's cheap and convenient, and those are big pluses.
>> 
>> However, I've been looking at using the NCO peripheral as a Pulse Density Modulated output instead. This would in theory produce a higher frequency output and allow a greater resolution.
>> 
>> In order to determine if the results I can get out of it are genuinely an improvement, I need to be able to accurately measure the performance of both styles of "DAC".
>> 
>> How would I do this?
>> 
>> My current method is to send an incrementing count to the DAC and then have a look at the post-reconstruction filter output on a 'scope. How wiggly the line is is my measure of quality! Not very exact!
>> 
>> I've got a digital oscilloscope, a multimeter, and a laptop. No other test equipment is available, unless I make it.
>> 
>> Thanks,
>> Tom
>> 
>> 
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