A novel safety system concept and implementation for implantable stimulators: A universal DC tissue leakage current detector

In this paper we describe a novel system concept and circuit implementation for detecting DC current leaking into tissue from implantable stimulators due to a fault. Such detection is critical as DC current passing into tissue from an electronic implant can cause permanent harm to the implant recipient. The proposed system detects any unintended DC current leaking into tissue regardless of the underlying failure mode and works regardless of how complex the implant is or how many electrodes it has. The implementation is a novel mixed-signal design containing analog parts (current DACs, accurate comparators, reference voltage generator, floating current source) as well as digital parts (linear filters and nonlinear controllers) and is suitable for direct integration into a low power implant ASIC. The analog circuitry was designed and simulated in a 0.35 mum high voltage process and the overall system operation, including the digital filters and nonlinear controllers, was modelled and verified in Simulink.