G. Degraaf et Rf. Wolffenbuttel, LIGHT-TO-FREQUENCY CONVERTER USING INTEGRATING MODE PHOTODIODES, IEEE transactions on instrumentation and measurement, 46(4), 1997, pp. 933-936
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.