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US 4,118,621 AGranted
Photo electric biased photo diode operational amplifier
AssigneeNational Semiconductor Corporation
InventorsDennis M. Monticelli, Robert S. Sleeth
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Abstract
A circuit useful in replicating the current produced in a photo diode operated as a current source at zero bias. A second scaled area photo diode is used to bias the circuit to maintain the zero bias over a wide range of illumination levels. The circuit operates in the picoampere range and is linear over at least six orders of magnitude.
Claims10
A circuit for replicating the photo current of an illumination responsive element which generates a photo current when exposed to illumination, said circuit comprising:
- a first photo diode adapted for exposure to said illumination to generate a current proportional to said illumination;
- amplifying means coupled to said first photo diode, said amplifying means including means to force the potential across said first photo diode to substantially zero volts thereby to provide linearity between said illumination and said photo current;
- and
- means for biasing said amplifying means substantially in proportion to said illumination, said means for biasing including a second photo diode adapted for exposure to said illumination and coupled to said amplifying means to provide illumination dependent bias thereto.
1 more element
Dependencies are inferred from the claim text.