Proposed wide dynamic-range controllable current sources

Generating ultra-low currents using resistors is impractical especially in integrated circuits due to the wasting of much area associated with the required very large resistors. In this paper, three ultra-low current sources that are suitable for biomedical and implantable applications are proposed. The generated currents are in the nanoampere range. One of the proposed current sources depends on a modification of the conventional Widlar MOS current source in which a tunable subthreshold-region operated transistor is utilized as a controlled resistance. The proposed current source is suitable for low-voltage and low-power applications. Also, two digitally controlled current sources (DCCSs) are proposed. The DCCSs find a wide variety of applications in digital-to-analog converters, implantable microstimulators, and charge pumps. The three proposed current sources are analyzed quantitatively. They are also verified by simulation adopting the 45 nm CMOS Predictive Technology Model (PTM) with a power-supply voltage, VDD, equal to 1 V.