Design and optimization of a low DC offset CMOS current-source dedicated to implantable miniaturized stimulators

The main goal of our study is the design of a current-source (CS) based on a miniaturized digital-toanalog converter (DAC). The primary application of this device is a wide range of neuromuscular implantable microstimulators. A great deal of attention was devoted to creating a flexible, compact, and energy efficient circuit. A new design method based on an optimization process involving area and linearity is thus proposed. Circuits obtained using this technique were characterized as having a 5-bit DAC resolution, with 2 mA peak output current, while requiring around 0.01 mm2 of chip area, using a 1.2 μm CMOS technology. This paper also extends the method to create an improved current-source, designed to minimize the output DC offset and charge accumulation that are noxious for the stimulated neuromuscular tissues. Our analysis of the proposed circuit configuration show that we can reach a small DC offset error, without using any coupling capacitor, which tend to be bulky, and not desirable in highly miniaturized implants.