Abstract
Abstract A silicon colour sensor can be realised based on the wavelength-dependent response of silicon photodiodes in the optical part of the spectrum rather than on the transmittance of dyes. Such a colour sensor has been reported before, however it lacked an output signal in a digital form. The wavelength dependence of the absorption coefficient causes a peaking of the response in silicon photodiodes. This is usually considered to be an undesirable effect and possibilities are explored for reducing the impact on silicon photodetectors. The opposite objective is pursued in the colour sensor and measures are taken to maximise the effect of this wavelength dependence in order to obtain colour sensors in silicon. A special read-out method has been used that allows the collection of only the charge carriers generated at certain depths. The ratio between the photocurrent that is due to charge carriers generated in a shallow layer of silicon and the total photocurrent, generated in this layer and the underlying silicon bulk, is used as the colour signal. The sensor operation can be combined with a dual-slope A/D converter for providing a digital output. The colour sensor has been tested against a set of Munsell colour cards and adjacent colours can be distinguished.
Published Version
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