One of the main research activity of the ibrAIn center is to investigate neural recording and neuromodulation technologies. This includes innovating an integrated multi-channel neural recording circuit and system, and stimulation through CMOS integrated circuits, and other technologies corresponding to recording and stimulation.
Why recording/stimulation is important?
Neural amplifiers are key elements in various studies in neuroscience and in neural prostheses, which are becoming increasingly popular for the treatment of many neurological diseases. Many neuroscientists have addressed the need to collect neuronal signals from as many electrode sites as possible to enhance the precision of decoding and deciphering brain signals. It is therefore becoming increasingly necessary to incorporate further recording channels into the neural recording integrated circuit (IC). Besides, neural stimulation can help in prevention of harmful neural activities, such as the ones associated with tremors and seizures.
The recording system, containing the recording amplifiers and ADCs, perform microelectrode array signal acquisition. Several issues need to be tackled from the viewpoint of circuit design for the deployment of implantable recording and stimulation devices with multiple channels such as high-density multi-channel recording and low-power consumption of recording system. Miniaturized implantable neural recording devices have to overcome these challenges.
What type of signals we are interested in? Acquisition requirements?
Extracellular action potential has a wide dynamic range of signal amplitudes from about 10uV to 10 mV. The most neuronal activity falls within the spectrum between 0.1 Hz and 10 kHz. The neural recording interface’s dynamic range is usually constrained by the signal noise. The cumulative noise at the input of a neural recording device consists of the neural potential field background thermal noise and the recording electrode thermal noise. This corresponds to a dynamic range of about 60 dB and requires an ADC with a resolution of 10bit. Moreover, completely differential architectures are needed, as they have a high common-mode rejection ratio (CMRR) and power-supply rejection ratio (PSRR) to suppress common-mode noise and interference from the power supply.
In the experimental implantable neural recording and stimulation microsystem, the recording and stimulation interfacing circuits need multi-channels to monitor different areas of the brain, a compact overall form factor to guarantee implantation is possible, and a low-power dissipation to prevent thermal tissue damage. To escape disruption at the interface of the electrode-tissue, the overall temperature rise in the cortex must be less than 1 C.
