Implantable measurement technique dedicated to the monitoring of electrode-nerve contact in bladder stimulators.

A fully integrated electrode-nerve contact monitoring circuit intended to increase safety and reliability in implantable bladder stimulators is described. The proposed integrated circuit converts a measurement of the impedance of two electrode-nerve contacts into frequency. The measurement is derived from a test current generated by the stimulation current source. The obtained results is the frequency of a square wave signal. This frequency is then converted into 8-bit data, which are serially transmitted to an external controller through an inductive link. The whole circuit can be set in idle model during stimulation, ensuring low energy consumption. It is fully testable, and an internal calibration technique makes it possible to reduce errors due to temperature and process variations. The total area of the proposed monitoring circuit is 0.1 mm2 when fabricated with a 0.35 micron technology, including a digitally controlled, current source. The design has been fabricated and successfully tested.