I do not understand the analysis of the R2R ladders. My main concern is that the different bits are seeing different resistances. If we look downwards all the resistances are 2R, but not upwards! For example the weight of b(n-2) should be (R+2R)||2R/((R+2R)||2R+2R)=3/8
For a 2 bit DAC the outputs would be:
0, 3/8, 4/8, 7/8
So looking upwards from the right end of a 2R resistor we see a resistance which depends on the distance of the output node. Thus the bits are not binary weighted.
Could somebody resolve this?