Output impedance linearization technique for current-steering DACs

Code and voltage dependence of the finite output impedance is a major contributor to current-steering DACs´ nonlinearity. This paper introduces a novel output impedance linearization technique that very effectively reduces this code and voltage dependence. The linearization is achieved by using a small linearization DAC switched with control signals opposite to those for the main DAC. The area and power overhead is less than 5% of the main DAC. Simulation results with a 14-bit segmented current-steering DAC in standard 0.18μm CMOS process show that the DAC´s integral nonlinearity due to finite output impedance is improved by almost 5 bits. Additional results also show that the linearization technique is very robust to random mismatch errors.