Circuitry for a remotely powered bio-implantable gastric electrical stimulation system

Power to bio-implantable devices is usually supplied through a battery implanted with the system or through wires extending to an outside power source. The latter case with wires protruding out of the body can be unaesthetic in appearance and can cause infection. In this research, we consider an alternative way to power a bio-implantable microsystem. It involves using rechargeable lithium batteries. Here, power is delivered remotely to charge implanted battery or batteries. This approach avoids periodic surgery necessary for battery replacement. It also does not tie a person to an external power source at all times. This improves patient’s quality of life. The present work involves design and fabrication of signal conditioning circuit for a remotely rechargeable, bio-implantable, Battery-powered Electrical Stimulation System (BESS). A rechargeable lithium ion battery with a voltage of 3.7 V powers the proposed circuit. The desired output, which goes directly to the electrodes, is a series of 10 V, 15 mA pulses with a duty cycle of 4.5 %. A second rechargeable lithium ion battery serves as back-up. A lithium ion charging chip is included which is connected to the designed IC through a logic interface. The two batteries work in tandem i.e. when one battery powers the IC the other gets recharged and vice versa thereby providing an uninterruptible output. The IC uses a series of charge pumps to get the required boost in voltage. The IC also includes voltage detector circuits to detect battery voltages, voltage regulator, pulse generator circuits, logic circuits and necessary switches. Individual subsystems of the IC were designed, simulated and fabricated using standard CMOS technology. Individual subsystem circuits were found to work satisfactorily except for the charge pump. A revised design is now under fabrication. The microsystem utilizes a hybrid approach. Experiments done with a bench-top circuit model to simulate the proposed IC showed that a 3 V battery with a capacity of 190 mAh could power the IC for 15 hrs and needed 4 hrs for recharging