A fast and safe discharge circuit for implantable stimulators using a depletion transistor

Maintaining charge balance is very important for chronic implantable stimulation applications. Passive discharge is a simple and reliable method for achieving charge balance. However, conventional passive discharge methods via a resistor or a MOS transistor require long discharge cycles, hence relatively low stimulation rates. We present a new fail-safe passive discharge circuit employing a depletion transistor which provides fast discharge, at least 50% faster than the other methods. A stimulator circuit was simulated in a 0.6-¿m silicon-on-insulator CMOS process to verify the new method. The circuit design and simulation results are presented.