An advanced demultiplexing system for physiological stimulation

A CMOS very large scale integration (VLSI) chip has been designed and built to implement a scheme developed for multiplexing/demultiplexing the signals required to operate an intracortical stimulating electrode array. Because the use of radio telemetry in a proposed system utilizing this chip may impose limits upon the rate of data transmission to the chip, the scheme described herein was used to reduce the amount of digital information which must be sent to control a large quantity (up to several hundred) of stimulating electrodes. By incorporating multiple current sources on chip, many channels may be stimulated simultaneously. By incorporating on-chip timers, control over pulse timing is assigned to the chip, reducing by up to fourfold the amount of control data which must be sent. By incorporating on-chip RAM, information associated with the desired stimulus amplitude and pulse timing can be stored on chip, In this manner, it is necessary to send control information to the chip only when the information changes, rather than at the stimulus repeat rate for each channel. This further reduces the data rate by a factor of five to ten times or more. The architecture described here, implemented as an eight-channel stimulator, is scalable to a 625-channel stimulator while keeping data transmission rates under 2 Mbps.