Patent US 4,237,495

A circuit for converting a series of photoelectric element array voltage outputs into twice the number of binary bits is described. Each photodiode output voltage is compared against two reference voltages to produce a two bit code word signifying a low, medium or high photodiode output. This is then operated on by a circuit implementation of a logic equation to produce a two bit serial output. The result is the frequency doubling of a photodiode array output for greater fidelity during transmission and reproduction of the original image.