High‐efficiency self‐powered oscillator for capacitive neural stimulation

Implantable neural stimulation devices have drawn attention for various clinical purposes. Capacitor-coupled stimulation inherently maintains charge-balance, allowing the use of less complex pulse-generating circuits. This Letter proposes a self-powered relaxation oscillator, which allows direct charge transfer from the energy harvester to the capacitive stimulation electrode. As the proposed circuit does not require power supply to operate the oscillator itself, it achieves high power efficiency by eliminating wasted current from the power supply to the ground. A prototype of the proposed oscillator was fabricated with a 0.35 μm standard CMOS process. The prototype chip demonstrates power efficiency of up to 94.1% at 520 Hz for 1.4 V signal swing.