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US 9,774,811 B1Granted
Ramp signal generator for double ramp analog to digital converter
AssigneeOmniVision Technologies, Inc.
InventorsHiroaki Ebihara, Zheng Yang
Life of this patent
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Abstract
Apparatuses and methods for image sensors with increased analog to digital conversion range are described herein. An example method may include disabling a first auto-zero switch of a comparator, the first auto-zero switch coupled to a ramp voltage input of the comparator, increasing, by a ramp generator, an auto-zero voltage level of a ramp voltage provided to the ramp voltage input of the comparator, and disabling a second auto-zero switch of the comparator, the second auto-zero switch coupled to a bitline input of the comparator.
Claims21
A method, comprising:
- disabling a first auto-zero switch of a comparator, the first auto-zero switch coupled to a ramp voltage input of the comparator;
- increasing, by a ramp generator, an auto-zero voltage level of a ramp voltage provided to the ramp voltage input of the comparator;
- disabling a second auto-zero switch of the comparator, the second auto-zero switch coupled to a bitline input of the comparator;
- increasing a ramp offset voltage level of the reference voltage provided to the reference voltage input of the comparator by the ramp generator;
- and
- comparing a voltage on the bitline input to the reference voltage on the reference voltage input.
3 more elements
A method, comprising:
- providing, by a ramp generator, a base reference voltage to a reference voltage input of a comparator, the reference voltage input including an NMOS transistor having a gate, wherein the base reference is coupled to the gate of the NMOS transistor;
- disabling a first auto-zero switch coupled to the reference voltage input of the comparator;
- adding, by the ramp generator, an auto-zero offset voltage to the base reference voltage;
- and
- disabling a second auto-zero switch coupled to a bitline input of the comparator.
2 more elements
An image system, comprising:
- a pixel array to capture image light and generate image charge;
- readout circuitry coupled to readout the image charge and convert the image charge to one or more digital signals corresponding to the image charge in response to a comparison of the image charge to a ramp voltage, the readout circuitry including:
- a comparator coupled to receive the ramp voltage at a reference signal input and the image charge at a bitline input, wherein the reference signal input and the bitline input are auto-zeroed before the comparison of the image charge to the ramp voltage by enabling respective reference input and bitline input auto-zero switches;
- and
- a ramp generator coupled to provide the ramp voltage to the readout circuitry, wherein the ramp voltage is increased by an auto-zero offset voltage after the reference input auto-zero switch is disabled but before the bitline input auto-zero switch is disabled.
2 more elements
Dependencies are inferred from the claim text.