A Retina/V1 simple cell chip for physiology experiment design or classroom demonstration

Abstract This chip provides retinal and simple cell responses to visual stimuli. It can be used by visual physiologists to debug and test their experimental setups and by instructors to demonstrate the responses of the early visual system. The chip has a hexagonal arrangement of 7 photodiodes. Subsequent processing produces the chip’s outputs: An adaptive photoreceptor cell, a retinal horizontal cell, onand off-type spiking retinal ganglion cells, and two spiking simple-type cells of odd and even type. The membrane potentials of some of the cells are also available. The 5 mm2 chip was built in a 1.6 m CMOS technology. All parameters are set by an on-chip bias generator. I. Motivation Modern visual physiology requires synchronization of multiple computers that generate visual stimuli, record responses, and perform on-line data analysis. These custom-built setups are usually ridden with irritating bugs that take months to expunge. There exist no commercially available animal “stand-in” devices that allow vision physiologists to test the complete experiment design from visual stimulus to on-line analysis of neural responses. Such a device would be valuable for debugging the setup before an animal is sacrificed for an experiment. Lecturers could also demonstrate compellingly the operation of retina and visual cortex. The aim of this work was to fabricate a practical device to fulfill these requirements, with battery-powered stand-alone operation, a number of easily selectable outputs, and preset operating point. II. Chip Architecture Fig. 1 shows the schematic of the core of the chip corresponding to the layout shown in Fig. 2. A discrete array of 7 hexagonally-arranged photodiodes feed their photocurrents to a linear array of 7 adaptive photoreceptor circuits (Fig. 3) [3]. The receptor outputs connect to the horizontal/bipolar layer circuits shown in Fig. 4. The horizontal cell circuit computes the average photoreceptor output using a follower-aggregator [5]. An antibump circuit [4] in each pixel splits the difference between photoreceptor and horizontal cell outputs into rectified on and