Image Sensor Saturation Detection via Black Pixel Circuit
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Solution Overview
Problem
Image sensors have varying saturation levels due to manufacturing environments, leading to a narrower dynamic range to ensure stable operation, which requires expensive devices for finer level detection.
Innovation Solution
A circuit and method for detecting the saturation level of an image sensor using a black pixel circuit with a detection controller, reset node, and pixel unit, allowing for the transfer of power or reference voltage to saturate and reset the photodiode, enabling the detection of correct saturation levels and setting dynamic ranges accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dynamic range is narrowed to ensure stable operation across different manufacturing variations, then reliability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent performs preliminary saturation detection using the black pixel circuit before normal image capture. By pre-determining the actual saturation level through controlled voltage application and measurement, the system establishes accurate reference values in advance, enabling precise measurement without narrowing the dynamic range.
Solution Approach 2:
The black pixel circuit serves as an intermediary measurement device that does not capture actual image data but provides saturation level information. This intermediary circuit enables accurate saturation detection without affecting the main image sensor's dynamic range and measurement precision.
2Measurement precision
If expensive devices are used to detect finer levels in a narrowed dynamic range, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The black pixel circuit uses the image sensor's own existing components (photodiode, floating diffusion node, reset switch) to perform saturation detection. By repurposing existing circuit elements rather than adding specialized detection devices, the system achieves accurate measurement without increasing device complexity.
Solution Approach 2:
The black pixel circuit is designed to serve multiple functions: it acts as both a normal pixel during image capture and as a saturation detection device when needed. This multi-functionality eliminates the need for separate expensive detection devices while maintaining measurement precision.
3Reliability
If the output range is reduced to maintain stable operation, then reliability is improved, but productivity deteriorates
Solution Approach 1:
The patent dynamically adjusts the output range based on the detected actual saturation level. Rather than using a fixed reduced range, the system adapts the operational parameters to match the specific sensor's characteristics, maximizing output range utilization while maintaining stability through real-time feedback.
Solution Approach 2:
The saturation detection circuit provides feedback about the actual saturation level to the image processing system. This feedback enables the system to optimize output range settings based on measured performance, achieving both stability and maximum productivity by operating at the true saturation boundary rather than an arbitrarily reduced range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate detection of saturation levels, preventing the narrowing of dynamic ranges and allowing image sensors to operate within their actual output ranges, thereby maintaining stability without the need for expensive devices.
Implementation Method 1
the photodiode PD of the image pixel circuit 131 is exposed to light, whereas the photodiode PD of the black pixel circuit 141 is blocked from light
Implementation Method 2
The photodiode PD of the image pixel circuit 131 generates charges caused by heat as well as charges caused by photoelectric conversion
Data Source
AI summary
A circuit and method of detecting a saturation level of an image sensor including a photodiode using a black pixel circuit included in the image sensor. The saturation level detecting circuit includes a pixel unit, a reset node and a detection controller. The pixel unit includes a floating diffusion node connected to, or disconnected from, the photodiode and outputs a voltage signal corresponding to the voltage of the floating diffusion node. The reset node is connected to, or disconnected from, the floating diffusion node. The detection controller transfers a power voltage or a reference voltage to the reset node.