A Neurostimulator for Deep Brain Stimulation With Wide Load Current and Impedance Adaptation Capability

In this work, a biphasic and bipolar current-controlled stimulator with high loading adaptability is proposed. The stimulator consisted of an on-chip high voltage generator, output driver and an 8-bit current DAC (Digital-to-Analog Converter), can constantly provide the required stimulus currents ranging from 0.1mA to a maximum of 20mA, as the loading impedance varied within 0.5kΩ - 5kΩ. With a nearly 12 V output voltage, the overstress and reliability issues of the circuits are thoroughly considered and carefully addressed in this work. To achieve high loading impedance adaptability, this paper proposes a novel PAM (Pulse Amplitude Modulation) loop control architecture to drive the charge pump (CP), which provides a significantly higher output dynamic range compared to conventional methods such as PFM (Pulse Frequency Modulation) and PSM (Pulse Skip Modulation). In addition, to further improve the Power Conversion Efficiency (PCE) of the high voltage generator, a new technique, PAM-based Dual-Domain Voltage Scaling (PAM-DDVS), is proposed to minimize unnecessary energy consumption while achieving high adaptive range. The fully-integrated stimulus chip with 2 output channels is fabricated in TSMC 0.18µm 1.8V/3.3V process, and occupies a core die area of approximately 1.6 mm². Imitation tests are conducted to validate the functionality of the stimulus chip.