Brain-computer interfaces (BCIs) face significant challenges in signal transmission due to the biological nature of nerve tissue. Unlike electronic circuits, nerve cells act as complex RC circuits, where direct digital signal transmission can cause electrical charge buildup, leading to electrolysis and degradation of the electrode-tissue interface.
Nerve signals, known as action potentials, operate within a specific frequency range. Research indicates that the effective working range for BCI input/output ports is approximately 220 to 9,000 Hz, with optimal processing often occurring between 220 and 4,000 Hz. These signals are highly sensitive to timing and phase variations.
The RHD2164 chip is a specialized multi-channel analog-to-digital converter used for neural signal acquisition. It utilizes a pseudo-differential mode to mitigate low-frequency noise, such as 50-60 Hz power line interference, by measuring signals relative to a reference electrode placed near the target tissue.
Achieving signal integrity requires impedance matching between the electrode contact and the receiver input. Contact resistance can vary significantly, ranging from 300 to 10,000 Ohms, and sometimes reaching tens of MegaOhms. Adjusting receiver input resistance can help correct signal amplitude and phase to improve data quality.
