Hardware Design of Real-Time Neural Signal Generator

Abstract: Brain Machine Interface (BMI) denominates a collection of systems which interface with the Central Nervous System (CNS). Implementation of a BMI involves the detection, extraction, processing, and translation of the signals from the Central Nervous System. A simulator to generate extracellular recordings is proposed by P.T.Thorbergsson, H. Jorntell, F.Bengtsson, M.Garwicz, J. Schouenborg, A.J Johansson in [1]. The described simulator is available as a script implemented in the numerical computing software "Matlab". To measure the performance of the BMI systems, the Matlab script is needed to be implemented on a Field Programmable Gate Array (FPGA) providing real-time signals. The first stage of the implementation on the FGPA requires a hardware design of the simulator. This report presents the hardware design of the Real-Time Neural Simulator. The Real-Time Neural Simulator the original Matlab script was to be adapted for the hardware design. The adaptation process involved replacing the Matlab closed source signal processing and mathematical functions with hardware implementable algorithms. The performances of these algorithms are successfully verified against the Matlab functions. The Neural Simulator Matlab script is converted from floating point to fixed point implementation and the performance is verified for different word lengths. One of the quantitative measurements for comparison of the output between original script and final fixed point script was the percent of energy difference of the output signal. For a word length of 13-bits with 1 sign, 6 decimal, and 6 fractional bits, the calculated difference is less than 5 percent depicting the strong resemblance between the outputs. Finally the hardware design of the simulator constitutes of interconnected hardware units. At the highest level a "Data Processing Unit" generates the target and the noise recordings, "Controller" enables, disables the processing modules and routes the data between them, and finally the RAM and ROM form the memory units to store the input and processed data.