Quality of 16 bit DACs?

Elmi

Hi,

as far as I understood, the P2 includes two 16 bit DACs. As the manual is not very detailled about these DACs: is there anything known about the quality of these DACs? In terms of linearity and noise?

Thanks!

MagIO2

Who's telling you this? What I read in the specs is:
"Each smart I/O pin has the following functions:
8-bit, 120-ohm (3ns) and 1k-ohm DACs with 16-bit oversampling, noise, and high/low digital modes"

What a coincidence ... just stumbled over this video which I did not watch yet, but will do soon:

pik33

P2 includes 64 DACs, not 2

These are physically 8 bit, but extended to 16 bit with 2 methods:

• adding a noise which average value matches lower 8 bits (you can actually hear how this works if you generate a 0.01 Hz sine wave and connect the output to the good quality amplifier with volume level set at 100%)
• adding a 256-clocks PWM switching between 2 8-bit values, so instead of noise, there is a PWM frequency in the signal. As the frequency is high (1 MHz when P2 clocked @ 256 MHz) every audio amplifier will filter it out.

The result is a very high quality audio DAC.

If the DACs resolution is not extended to 16 bits, they are fast enough to become video DACs which can give sharp, good quality VGA video up to full HD.

evanh

On that note, part of the reason it likely works so well is the impedance of the DACs isn't as low as the logic drive. It'll take the edge off the square PWM. It may be worth experimenting with all the DAC drive strengths.

Bob Drury

This Video was very interesting shows how much thought has gone into the P2. Where do you find this? Are all the video's cataloged somewhere?
Regards
WRD Bob Drury

tritonium

Hi
Try this:-

Dave

MagIO2

All on youtube: https://www.youtube.com/c/ParallaxInc/playlists
Go to playlist "Propeller 2 Early adopter series"

Tubular

For clarity there are in fact 2 output DACs in every pin, as well as a slower comparator DAC
1. There is a 990 ohm, 3v3 range DAC, that can switch in a shunt resistance to become a 2v, 600 ohm dac
2. There is a 124 ohm, 3v3 range DAC, that can switch in a shunt resistance to become a 2v, 75 ohm dac (good for video, vga)
the above two are super fast, and can dither to achieve more than 8 effective bits. These are the four standard DAC output modes (990/600/124/75 ohm)

There is also a slower 8 bit DAC used with the "Pin A > D" input comparator mode, where the D level is set by this slower DAC

The DACs are good but we can make them even better, I'll publish some info on this soon