A versatile monolithic IC building-block for light-sensing applications

An all-bipolar building-block consisting of a linear light-to-current converter, a voltage comparator, and a voltage reference has been developed. This new general purpose IC combines the advantages of silicon photodiode light sensors with the linear signal processing capability of bipolar integrated transistors. In achieving this marriage, new circuit techniques were developed in order to operate at the very low current levels (<1 nA) and over the wide dynamic range of the light input. Besides their normal sensory function, photodiodes were made to serve as active elements in the circuit, taking part in biasing and acting as active loads in circuits that operate entirely on photocurrents. Use of these techniques boosted overall performance and eliminated the need for a light shield over the active-device portion of the die.