Current ratio circuit for multi-color imaging

Details Current ratio circuit for multi-color imaging Current ratio circuit for multi-color imaging

1994-12-12

1996-03-26

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

250226, 327514, G01J 350

Patent

active

055022995

ABSTRACT:
An electronic circuit extracts a ratio of currents from two sources and provides an output that is a function of the current ratio. An embodiment of the circuit includes a source current that may be provided by a blue-green photodetector and a sinking current that may be provided by a red photodetector. The source current feeds the input of a current splitter formed by a pair of PFETs. A portion of the source current is fed from the current splitter to a current ratio extractor implemented in CMOS. The remaining portion of the current from the current splitter is fed to a node shared with the sinking current and a second input to the current ratio extractor. The current ratio extractor produces an output voltage that is a function of the ratio of the photodiode currents and is substantially independent of the total current. The output voltage provides color information that may be used in low-cost machine vision systems for tasks such as sorting objects based on color or detecting object boundaries while rejecting shadows and reflective glints.

REFERENCES:
patent: 4660075 (1987-04-01), Hashimoto et al.
patent: 4677289 (1987-06-01), Nozaki et al.
patent: 5381054 (1995-01-01), Standley
Perez et al., "Toward Color Image Segmentation in Analog VLSI: Algorithm and Hardware," International Journal of Computer Vision, 12:1, pp. 17-42 (1994).

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