An implantable pulse generator for providing at least one of a voltage and a current stimulation to a tissue of a subject through trough at least two electrodes adapted to be in electrical contact with the tissue of the subject, the implantable pulse generator comprising a stimulation circuit coupled to the at least two electrodes, the stimulation circuit including at least one dual-mode voltage and current source, wherein the stimulation circuit can operate alternatively in a voltage stimulation mode and in a current stimulation mode. The implantable pulse generator also comprises a processing unit coupled to the stimulation circuit, the processing unit being so configured as to control the mode of operation of the stimulation circuit. The implantable pulse generator may also comprise a monitoring unit coupled to the stimulation circuit and the processing unit; the monitoring unit being so configured as to provide feedback signals relating to electrical characteristics of the tissue from the stimulation circuit to the processing unit.