Ifi Research: Microelectronic Systems: Nanooelectronic Systems: Neuromorphic Systems: Student Projects
This is a project in connection with a collaboration with the company LifeCare. The aim of the collaboration is to develop a glucose sensor that is implantable and allows continuous monitoring of glucose levels in the blood of diabetes patients. The continuous monitoring allows a finer administration of insulin and avoids big swings in the glucose levels. The later have severe consequences on the patients health in the long run. By avoiding these swings the life expectancy of the patients can be increased by several years.
A permanent implant cannot require cables through the skin. Thus, the communication and the supply with energy has to be wireless. We intend to solve this with an inductive link, i.e. two coils, one on the skin and the other just under the skin. This solution has been used already very successfully for example in cochlear implants. The coils allow an AC signal to be transfered through the skin. One component of the inside has to transform this AC signal into a stable, temperature independent DC power-supply for the implant with as big an efficiency as possible. This is achieved in two steps: first we use a so called bandgap voltage reference that provides a stable reference voltage of 1.0V, indpendent of its own power-supply (which can range from 2.0V to 3.5V) or temperature variations. But that circuit cannot supply any output current. thus, in a second step, that reference voltage has to be buffered by a power amplifier.
We have already produced two prototypes of the implant's integrated circuit. The power regulation, however, still suffers from some problems: we do achieve a very stable reference voltage, but the power amplifier's output voltage still shows considerable ripple, mainly due to an insufficient capacitance at it's output. This capacitance, however, cannot simply be increased, since the implant cannot carry bigger discrete capacitors due to space limitations.
The aim of this project is to propose a solution to improve the power amplifier rather than to increase the capacitance of the regulated power supply to reduce ripple. It will involve ASIC and PCB design and testing.