Data Rate Reduction in Intracranial Digital Neural Probes using Delta Encoding

To resolve action potentials, neural recording systems require microvolt resolution. Although the maximum amplitudes of action potentials and local field potentials are in the millivolt range, such systems typically cover a much larger full scale to account for electrode offsets, drifts, and artifacts. The number of bits required to cover this range is much larger than the actual bits required to represent the data. This means that miniaturized probes with in-situ digitization require not only a larger digital area, but also a large amount of power to transmit the data to the host. This paper presents a method for reducing the data rate in neural probes with direct A/D conversion based on digital delta encoding. Data sets from in-vivo experiments are statistically analyzed to determine the number of bits sufficient for delta data transmission. Furthermore, a control system is presented that implements automatic common-mode adjustment and compensates for electrode offsets and drifts, enabling delta encoding with DC-coupled recording.