| Summary: | Implantable electrical stimulators can be used to treat a variety of neurological disorders and restore paralyzed body functions. In electrical neural stimulation, the stimulator circuit with safe charge balancing is essential to minimize damage to electrodes and biological tissue. In this paper, an implantable current-mode neural stimulator for long-term safe electrical stimulation is presented. Anodic current pulse modulation active charge balancing technique is proposed to keep the residual voltage on the electrode within the safe window, which enables long-term safe stimulation. To ensure more complete charge balancing, the proposed active charge balancing technique can also be used with passive electrode shorting. Transistor stacking and dynamic gate biasing techniques can prevent the breakdown of standard MOSFET devices from high supply voltages, which enable the implementation of output current driver and charge balancing circuits without using HV process. The stimulator IC designed with 0.18-μm standard CMOS process can generate up to 1 mA of stimulation current and only consumes an area of 0.11 mm<sup>2</sup>. Since all functions are implemented on-chip without using external components, the proposed stimulator IC is suitable for high-density implantable stimulation applications.
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