A high performance ASIC for electrical and neurochemical traumatic brain injury monitoring

Abstract

Traumatic Brain Injury (TBI) can be defined as a non-degenerative, non-congenital brain trauma due to an external mechanical force. TBI is a major cause of death and disability in all age groups and the leading cause of death and disability in working people and among young adults. This Thesis presents the first application specific integrated chip (ASIC) for monitoring patients suffering from TBI. The microelectronic chip was designed to meet the demands of processing physiological signals for an alternative method of TBI monitoring. It has been studied that by monitoring electrical (ECoG) and chemical (glucose, lactate and potassium) signals, the report of spreading depolarisation (SD) waves could be a good indicator for an upcoming secondary brain injury. The ultimate aim of this Thesis has been to support the idea of a “behind-the-ear” micro-platform, which could enable the monitoring of mobile (or mobilized) patients suffering a TBI who, currently, are not monitored. Switched-capacitor (SC) circuits have been adopted for the implementation of both current and voltage analogue front-ends (AFEs). Advanced techniques to minimise noise and improve the noise performance of the circuit were employed. Moreover, a digitally enabled automatic transimpedance gain control circuit, suitable for current analogue front-ends, was developed and tested in order to provide an automated way to adjust the gain and to counterbalance for the drop in sensitivity of the biosensors due to drift. Measured results confirming the operation of the TBI ASIC and its sub-circuits are reported. Finally, a novel circuit that mimics the Butler-Volmer dynamics is presented. The basic building blocks arise from the combination of Translinear (TL) Circuits and the Non- linear Bernoulli Cell Formalism (NBCF). The developed electrical equivalent circuit has been compared to an ideal model, which was developed in MATLAB. The robustness of the microelectronic system was evaluated by means of Monte Carlo simulations.