An array of light-intensity sensors based on flip-flops

A RAM-compatible light-intensity sensor array with a digital output, based on flip-flops consisting of silicon phototransistors and implanted resistors, is presented. The sensor is based on bringing a flip-flop into the highly sensitive unstable state, from which it will switch to a `one' or `zero', depending on the perturbation. The sensing elements are incorporated in the flip-flop to generate a perturbation. The advantages of the technique include a digital output, a high sensitivity, and a simple structure. By virtue of their small size, a large number of flip-flop sensors can be integrated in an array. The experimental device contained 64 flip-flops organized in an 8×8 matrix and was used for the measurement of a two-dimensional optical image. Performance and operating characteristics are reported