Go Down

Topic: DAC support (Read 15 times) previous topic - next topic

parasound

Ok.
Thank you wibauxl.

retrolefty

#11
Nov 12, 2012, 03:16 pm Last Edit: Nov 12, 2012, 04:24 pm by retrolefty Reason: 1

Hi parasound and andy_g,

I could find no information about the DAC range in the SAM3X datasheet.
But on page 1059 of SAM3S datasheet, it is said that the voltage range of the DAC is from (1/6) x VADVREF to (5/6) x VADVREF.
So I suspect, the same applies to SAM3U, and range is 1/6 x 3.3V = 0.55V to 5/6 x 3.3V = 2.75V, which is verified by your measures.

wibauxl


That seems pretty limiting. You mean one can't measure output signals between below .55 volt? There must be more to the subject then that?

Lefty

Massimo Banzi

@retrolefty

We're talking about the DAC here. The ADC works at voltages below 0.55v.
As far as the DAC is concerned it's a pity to have such limits but I guess for audio applications there are way to circumvent the issue.

m

retrolefty

#13
Nov 12, 2012, 04:30 pm Last Edit: Nov 12, 2012, 04:34 pm by retrolefty Reason: 1

@retrolefty

We're talking about the DAC here. The ADC works at voltages below 0.55v.
As far as the DAC is concerned it's a pity to have such limits but I guess for audio applications there are way to circumvent the issue.

m


Well I don't yet own a Due and not up to the task just yet of taking on the huge datasheet for this uP, but they must talk about this range restriction if indeed it's a hardware based restriction. I just find it very hard to except at this time that there is a legitimate reason for this. I guess it could be compensated for with external op-amp with a -.55v offset, but still there just must be more to this subject then 'that's just the way it is'? It's really not a problem for audio type applications as one could just capacitance couple the signal, but for precision DC DAC applications, not being able to reach ground potential is a pretty big deal, no?

Lefty

andy_g

...what would also make sense resolution-wise: LSB seems to be 0.5mV (measured) which is in line with wibauxl's theory ((2.75-0.55)/4096=0.537mV). This DAC behaviour -and te lack of it's documentation- is a little odd to my opinion, but at least there's an explanation that makes sense.

MANY THANKS FOR ALL YOUR INPUTS!!

andy_g

Go Up