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US 5,886,659 AGranted
On-focal-plane analog-to-digital conversion for current-mode imaging devices
AssigneeCalifornia Institute of Technology
InventorsBedabrata Pain, Junichi Nakamura, Eric R. Fossum
Life of this patent
Estimating the term…
Abstract
A current-mode analog-to-digital converter based on a current copier circuit with a constant bias current that is independent of the input signals. A second-order incremental .SIGMA.-.DELTA. conversion configuration is implemented. An array of such analog-to-digital converters can be integrated onto the focal plane of an imaging sensor array to achieve column-wise parallel analog-to-digital conversion.
Claims12
A circuit, comprising:
- an input and output terminal;
- a memory cell connected to said input and output terminal, said memory cell having a memory capacitor that stores charges from said input and output terminal, a memory transistor connected to said memory capacitor and configured to control current in said memory capacitor;
- and
- a copier cell connected to said input and output terminal, said copier cell having a copier capacitor, a copier transistor connected to said copier capacitor and configured to control a current in said copier capacitor, and a bias element that produces a bias current in said copier cell that is substantially independent of an input current from said input and output terminal,
- wherein said memory cell and said copier cell are operable to produce an output current that deviates from said input current by a constant bias.
2 more elements
A circuit, comprising:
- an input terminal, receiving an input current;
- a current integrator connected to said input terminal and configured to perform integration of said input current;
- a current comparator receiving an integrated current from said current integrator and producing a digital output according to a comparison of said integrated current with a reference current;
- and
- a negative feedback loop including a current digital-to-analog converter that operates based on said reference current and feeding an analog representation of said digital output from said current comparator to said input terminal, said feedback loop operating to minimize noise in said digital output.
2 more elements
A circuit, comprising:
- a semiconductor substrate;
- a sensing array formed on said substrate and configured to have a plurality of photosensitive pixels, said sensing array operating to receive an input image and produce a corresponding current array indicative of said input image;
- at least one current-mode analog-to-digital convert formed on said substrate and connected to at least one pixel of said sensing array, said converter operable to convert analog current signals into digital signals which forms a digital representation of said input image.
Dependencies are inferred from the claim text.