LIGHT-TO-FREQUENCY CONVERTER USING INTEGRATING MODE PHOTODIODES

An optical sensor for operation in the visible spectrum with integrate d electronic readout circuits has been realized in a BIFET process, Th e output signal is a pulse series with a frequency proportional to the intensity of the incident light, Furthermore, the duty-cycle of the o utput pulses depends on the spectral distribution of the incident ligh t, enabling the measurement of color, The electronic circuits have bee n designed for operating with a large dynamic range, while using only a relatively small chip area, No internal or external capacitor is nee ded for the current-to-frequency conversion, since the photodiode oper ates in the charge integrating mode, This enables fabrication of array s of smart image detectors where a large area can be used for the phot odetector.