Image Sensor Ramp Detection for Dark Sun Readout Errors
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Solution Overview
Problem
Image sensors experience the 'dark sun effect' due to strong light irradiation, causing floating diffusion nodes to discharge and resulting in reading errors, particularly in bright areas of images.
Innovation Solution
An image sensor and sensing method that include a first and second pixel circuit, a ramp signal generating circuit, a comparator, and a signal processing circuit, which provide ramp signals through capacitors to floating diffusion nodes during normal readout and dark sun detection periods, allowing the comparator to determine and correct for the dark sun effect by adjusting digital values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the image sensor is used to sense strong light, then the sensing capability is improved, but the dark sun effect occurs causing reading errors
Solution Approach 1:
The patent applies preliminary action by performing a dark sun detection period before the normal readout period. During this detection period, the floating diffusion nodes are reset and ramp signals are applied to detect potential dark sun effects before actual image sensing occurs. This preliminary detection and reset process prevents the dark sun effect from affecting subsequent reading accuracy when sensing strong light.
2Object-affected harmful factors
If transfer transistors are not turned on during strong light irradiation, then the dark sun effect is avoided, but floating diffusion nodes discharge causing reading errors
Solution Approach 1:
The patent implements feedback by using a comparator to continuously monitor the voltages of floating diffusion nodes during both the dark sun detection period and normal readout period. When the comparator detects that a floating diffusion node voltage exceeds a threshold (indicating discharge due to dark sun effect), it generates a signal to the signal processing circuit, which then corrects the affected pixel values by adding the overdrive voltage, thereby maintaining reading accuracy.
3Productivity
If ramp signals are applied during normal readout period, then pixel reading is enabled, but dark sun effect cannot be detected
Solution Approach 1:
The patent applies periodic action by dividing the operation into distinct periods: a dark sun detection period followed by a normal readout period. During the detection period, ramp signals are applied and comparator detection is enabled to identify dark sun effects. During the subsequent readout period, normal pixel reading occurs. This periodic alternation between detection and readout modes enables both dark sun effect detection and efficient pixel reading without interference.
Data Source
AI summary
An image sensor and an image sensing method are provided. The image sensor includes a first pixel circuit, a second pixel circuit, a ramp signal generating circuit, a comparator, and a signal processing circuit. The first pixel circuit has a first floating diffusion node. The second pixel circuit has a second floating diffusion node. The ramp signal generating circuit respectively provides a first ramp signal and a second ramp signal to the first floating diffusion node and the second floating diffusion node during a dark sun detection period. The comparator receives a first node voltage of the first floating diffusion node and a second node voltage of the second floating diffusion node. The signal processing circuit determines whether to output an output signal and determines whether to overwrite a digital value corresponding to a sensing signal according to whether the comparator is triggered.