The R resistor to ground in R-2R AOut LC

[widdly]

Looking at different analysis of R-2R DAC's on the web, they all use a 2R for the resistor to ground. I notices in the AOut-LC it uses a 1R. Wouldn't that make the scaling of the bits all wrong?

[nILS]

Yes and no. The steps aren't equally spaced with 1R to ground, that's right. Every other step is a "bit higher". It does bring the benefit of being able to have different configurations (2x8 bits that are identical, 1x12 + 1x4 bits). If you don't need the options you can easily adjust the 2 resistors to ground to get equal steps.

[widdly]

Yes and no. The steps aren't equally spaced with 1R to ground, that's right. Every other step is a "bit higher". It does bring the benefit of being able to have different configurations (2x8 bits that are identical, 1x12 + 1x4 bits). If you don't need the options you can easily adjust the 2 resistors to ground to get equal steps.

Couldn't you just add another R resistor between the ground and pin 1 and between the ground and pin 5? That way you could have both equal steps and different configurations.

Edited August 5, 2010 by widdly

[nILS]

Yep, that's correct. I was just assuming that what I described was TK's intention - I might be wrong with that though. Thanks for bringing it up though, I am pretty sure TK will look into it once he gets back :)