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

[Tom Wiltshire]

Thank very much to everyone that helped me with this.

With your pointers, I was able to establish using the FFT function on my scope that 10-bit PWM at 31.25KHz gives me background hash at a level -41dB wrt my sine signal, and that 10-bit PDM pushes that down to -64dB. That's not bad for something that is just one IO pin on a PIC with a passive RC filter hanging off it.

I'm now going to experiment to see if I can squeeze more resolution out of it too, and if that helps further.

Tom



On 25 Apr 2017, at 14:09, 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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