An optical flip-flop sensor array with digital outputs

A two-dimensional optical flip-flop sensor array is presented. It consists of 64 flip-flop sensors, each of which contains two phototransistors with different light sensitivity. Each flip-flop sensor senses the light intensity and converts it to a series of ones and zeros. It is operated by turning on and off the supply current with a high frequency. During the absence of light, the flip-flop is totally symmetrical, and as a result the number of ones and zeros is equal. Light causes an asymmetry in the flip-flop that changes the ratio of ones and zeros. A fully digital output is obtained by counting the number of ones. A triangle-wave voltage is applied to the flip-flop in order to vary the threshold of the flip-flop. It is demonstrated that a large array of sensors with on-spot A/D conversion can be realized using the flip-flop sensor technique