COLOR-SENSOR SYSTEM WITH A FREQUENCY OUTPUT AND AN ISS OR (IC)-C-2 BUS INTERFACE

An optical sensor for operation in the visible spectrum with integrate d electronic readout circuits and two different interfaces to a sensor bus system has been realized in a BIFET process. The output signal of the basic readout circuit is a pulse series with a frequency proporti onal to the intensity of the incident light. Furthermore, the duty cyc le of these output pulses depends on the spectral distribution of the incident light, enabling measurement of colour. No internal or externa l capacitor is needed for the current-to-frequency conversion, since t he photodiode operates in a charge-integrating mode. The electronic ci rcuits have been designed for operating with a large dynamic range and a relatively small chip area. Interfaces to the ISS and the (IC)-C-2 bus have been designed, fabricated and tested in the same process. Pho todiodes with different spectral responses have also been fabricated o n a single chip in a standard CMOS process. First measurements on thes e devices have shown that the same readout principle can be used in CM OS technology. These results will be published later. In CMOS technolo gy a much smaller die area is needed if the sensor, the readout circui ts and the digital interface are integrated on a single chip.