Active Books: The Design of an Implantable Stimulator That Minimizes Cable Count Using Integrated Circuits Very Close to Electrodes

• Published in: IEEE transactions on biomedical circuits and systems 2012-06, Vol.6 (3), p.216-227
• Main Authors: Xiao Liu, Demosthenous, A., Vanhoestenberghe, A., Dai Jiang, Donaldson, N.
• Format: Article
• Language: English
• Subjects: Active Book; Anodes; Biomedical Engineering; Capacitors; Cauda Equina - pathology; Clocks; Computers; crosstalk; Current measurement; distributed stimulation system; Electric Power Supplies; Electric Stimulation; Electrodes; Electrodes, Implanted; Electronics, Medical - instrumentation; Equipment Design; Humans; Humidity; humidity measurement; Implantable Neurostimulators; implanted device; integrated circuit; Male; Motor Neurons - pathology; nerve root stimulator; passive discharge; Power supply; Semiconductor device measurement; Signal Processing, Computer-Assisted; spinal cord injury; tripole; Wireless Technology; Wires
• ISSN: 1932-4545; 1940-9990
• DOI: 10.1109/TBCAS.2011.2174360

This paper presents an integrated stimulator that can be embedded in implantable electrode books for interfacing with nerve roots at the cauda equina. The Active Book overcomes the limitation of conventional nerve root stimulators which can only support a small number of stimulating electrodes due to cable count restriction through the dura. Instead, a distributed stimulation system with many tripole electrodes can be configured using several Active Books which are addressed sequentially. The stimulator was fabricated in a 0.6-μm high-voltage CMOS process and occupies a silicon area of 4.2 × 6.5 mm 2 . The circuit was designed to deliver up to 8 mA stimulus current to tripole electrodes from an 18 V power supply. Input pad count is limited to five (two power and three control lines) hence requiring a specific procedure for downloading stimulation commands to the chip and extracting information from it. Supported commands include adjusting the amplitude of stimulus current, varying the current ratio at the two anodes in each channel, and measuring relative humidity inside the chip package. In addition to stimulation mode, the chip supports quiescent mode, dissipating less than 100 nA current from the power supply. The performance of the stimulator chip was verified with bench tests including measurements using tripoles in saline.