Many embodiments of the invention provide a neuromodulation system that includes a digital control unit (DCU) that activates a stimulation engine during active stimulation, a current mirror that includes two feedback loops including a first feedback loop with positive feedback (PF) made of an error amplifier A1 and transistors M3 and M1 and a second feedback loop with a negative feedback (NF) made of the error amplifier A1 and transistor M3, and a high-voltage adaptive rail (Vdd/Vss) to accommodate voltage drops across high electrode impedances.