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

[Scott Gravenhorst]

I make basic measurements which include spectrum using free RightMark
Audio Analyzer (on a PC).  I had been working with someone who wanted
to use a one bit first order delta-sigma DAC on an FPGA project and I
was able to show that there were large amounts of harmonic signal
present even though the input to the DAC was a sine wave.  RMAA is
probably not the best, but I think it's output would be better than
looking at wigglies on an oscope.

Tom Wiltshire <tom at electricdruid.net> wrote:
>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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-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- http://scott.joviansynth.com/
-- When the going gets tough, the tough use the command line.
-- Matt 21:22