ABSTRACT
The photointegrated circuit (photo IC) offers some characteristics that can be very useful in certain applications. In many designs, the photoswitch must be in a remote location from the processing electronics. The high-resolution rotary or linear encoders use photo ICs to take advantage of the inherent speed, the reduced system space, reliability, and cost reduction attained over systems fabricated from discrete devices. The P-N photodiode is similar in structure to the P-N transistor, with two major exceptions. First, it is significantly larger to absorb more photons and, second, the N+-type diffusion used for the emitter is eliminated. A number of different simple photo IC circuits are similar in function to the phototransistor and photodarlington. Popular photo IC designs incorporate a Schmitt trigger, which provides a hysteresis characteristic to improve the performance across varying input signals. The photo IC with hysteresis characteristics is available with and without a built-in voltage regulator.
