[SOLVED] sar adc design using unit length DAC array

[xnz]

Hi everyone. I am now using a unit-length DAC array for the sar adc in order to minimize the area of the DAC array. However, there is always an offset error about 4LSB even I am using ideal components.

Anybody has experience with this kind of DAC array?

PS: the paper about is from Pieter Harpe