Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1994-12-19
1997-07-22
Allen, Stephone
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
2502082, 2502085, 356222, H01J 4014
Patent
active
056506082
ABSTRACT:
A ratiometric sensor is formed of a first photodiode connected in series with an electronic component, such as a second photodiode or a resistor, between a source of first voltage and a source of second voltage. The ratiometric sensor supplies a "ratiometric voltage" on a ratiometric sensor output line that is connected to a junction between the first photodiode and the electronic component. The ratiometric voltage is proportional to the ratio of the equivalent resistance of the first photodiode to the sum of the equivalent resistances of the first photodiode and the electronic component. A ratiometric sensor that uses a photodiode and a resistance has a large dynamic range because the ratiometric voltage can vary between the first voltage and the second voltage. A ratiometric sensor that uses two photodiodes is less sensitive to noise than a conventional circuit that uses a single photodiode, because noise can get canceled from the numerator and denominator of the ratio. The ratiometric signal can be digitized by an analog-to-digital converter that can include, for example, a 555 timer, a Darlington transistor or a combination of a resistor and a capacitor.
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Redford Peter M.
Stern Donald S.
Allen Stephone
MacPherson Alan H.
Suryadevara Omkar K.
TV Interactive Data Corporation
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