Design of a Closed Loop, Bidirectional Brain Machine Interface System With Energy Efficient Neural Feature Extraction and PID Control
This paper presents a bidirectional brain machine interface (BMI) microsystem designed for closed loop neuroscience research, especially experiments in freely behaving animals. The system on chip (SoC) consists of 16 channel neural recording front ends, neural feature extraction units, 16 channel programmable neural stimulator back ends, in channel programmable closed loop controllers, global analog digital converters (ADC) and peripheral circuits. The proposed neural feature extraction units includes 1) an ultra low power neural energy extraction unit enabling a 64 step natural logarithmic domain frequency tuning, and 2) a current mode action potential (AP) detection unit with time amplitude window discriminator. A programmable proportional integral derivative (PID) controller has been integrated in each channel enabling a various of closed loop operations. The implemented ADCs include a 10 bit voltage mode successive approximation register (SAR) ADC for the digitization of the neural feature outputs and/or local field potential (LFP) outputs, and an 8 bit current mode SAR ADC for the digitization of the action potential outputs. The multi mode stimulator can be programmed to perform monopolar or bipolar, symmetrical or asymmetrical charge balanced stimulation with a maximum current of 4 mA in an arbitrary channel configuration. The chip has been fabricated in 0.18<inline formula><tex math notation="LaTeX"\mu$/tex math>/inline formula> m CMOS technology, occupying a silicon area of 3.7 mm<inline formula><tex math notation="LaTeX"^2$/tex math>/inline formula> The chip dissipates 56 <inline formula><tex math notation="LaTeX"\mu$/tex math>/inline formula>W/ch on average. General purpose low power microcontroller with Bluetooth module are integrated in the system to provide wireless link and SoC configuration. Methods, circuit techniques and system topology proposed in this work can be used in a wide range of relevant neurophysiology research, especially closed loop BMI experiments.
IEEE Transactions on Biomedical Circuits and Systems