A simple integrated color indicator

A simple integrated color sensor, suitable for providing a one-dimensional electrical output proportional to the color impression obtained from an observed scene, will in many applications be as effective as a high-density two-dimensional color imager. Such an all-silicon color sensor based on the strong wavelength dependence of the penetration depth of incident optical radiation in silicon is described. The sensor consists of two similar reverse-biased photodiodes with junctions at the same depth. A selected nonunity ratio between the photocurrents in the depleted regions is pursued using unequal reverse voltages. The sensor and the required electronic functions are integrated in a bipolar integrated circuit providing a voltage proportional to the average of the optical power distribution of the incident light within an electronically tunable part of the spectrum.