Electrical Components for a Fully Implantable Neural Recording System

The human brain has long been a subject of study and fascination. There are certain tasks for which our brains vastly outperform inanimate machines, and the brain is very computationally efficient, dissipating 12 W of power versus > 50 W of power for a modern microprocessor. A better understanding of how the brain functions has the potential to advance many branches of engineering. In recent years, the advent of microelectrode arrays has allowed researchers to begin understanding how the brain processes information. These arrays allow long-term simultaneous recording of neural activity from many neurons simultaneously. The ideal system for long-term multiunit recording would be a fully implantable device which is capable of amplifying the neural signals and transmitting them to the outside world. This work investigates several of the building blocks necessary for the micro-electronic components of such a system. An overview is given of the components and requirements for a fully implantable recording system. The bias circuitry for the electronics of a fully implantable recording system is designed and implemented. This is done by surveying a number of designs for each circuit component, evaluating each design against the requirements for a fully implantable recording system, and then choosing the most suitable topology for design and implementation. We also design and test a fully differential low-noise amplifier for use in these systems. The amplifier is based on a previously reported single-ended version, and has the advantage of rejecting interference caused by the digital circuitry of the recording system. The fully differential amplifier is implemented with three different common mode feedback circuits. Two common mode feedback circuits are standard designs, and the third is a novel design based on floating gates. The floating gate common mode feedback circuit combines the advantages of the two tested standard common mode feedback circuits, by combining a large allowable output signal swing with continuous time operation.