Design and evaluation of wide-range and low-power analog front-end enabling body-implanted devices to monitor charge injection properties

Abstract

For safe electrical stimulation with body-implanted devices, the degradation of stimulus electrodes must be considered because it causes the unexpected electrolysis of water and the destruction of tissues. To monitor the charge injection property (CIP) of stimulus electrodes while these devices are implanted, we have proposed a charge injection monitoring system (CIMS). CIMS can safely read out voltages produced by a biphasic current pulse to a stimulus electrode and CIP is calculated from waveforms of the acquired voltages. In this paper, we describe a wide-range and low-power analog front-end (AFE) for CIMS that has variable gain-frequency characteristics and low-power analog-to-digital (A/D) conversion to adjust to the degradation of stimulus electrodes. The designed AFE was fabricated with 0.18 µm CMOS technology and achieved a valuable gain of 20-60 dB, an upper cutoff frequency of 0.2-10 kHz, and low-power interleaving A/D conversion. In addition, we successfully measured the CIP of stimulus electrodes for body-implanted devices using CIMS.

Study of Al-doped ZnO Transparent Stimulus Electrode for Fully Implantable Retinal Prosthesis with Three-dimensionally Stacked Retinal Prosthesis Chip

“…CIC values were measured by a conventional method with 0.01 M PBS at 23 °C. (19) The used-input biphasic current pulse consisted of a 200 μs positive current pulse, a 200 μs negative current pulse, and a 20 μs interval between the positive and negative current pulses. In general, the input current depends on the maximum cathodic potential (E mc ) of the electrode material.…”