Solid-State Image Sensor Constant Current Source W/L Ratio Control
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Solution Overview
Problem
Existing solid-state image sensors face challenges in increasing dynamic range without decreasing the aperture ratio, as techniques requiring transistors or large capacitors for switching conversion efficiency compromise pixel performance.
Innovation Solution
A solid-state image sensor with a pixel array and constant current source circuit unit, where the ratio of gate width to gate length of transistors in the constant current source is adjusted based on illumination conditions to optimize input voltage range and noise without altering the pixel circuit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transistor for switching conversion efficiency or a large capacitor is added to switch between low and high conversion efficiency, then the dynamic range is increased, but the aperture ratio of the pixel is lowered
Solution Approach 1:
The patent changes the W/L ratio parameter of the constant current source transistor to control conversion efficiency. By adjusting this single parameter, the system can switch between high conversion efficiency (for low illumination) and low conversion efficiency (for high illumination) modes without adding any physical components to the pixel, thus maintaining the aperture ratio while achieving variable dynamic range
Solution Approach 2:
The constant current source transistor serves multiple functions: it provides the constant current for the pixel circuit operation and simultaneously acts as a conversion efficiency control element by changing its W/L ratio. This multi-functionality eliminates the need for separate switching transistors or capacitors, preventing aperture ratio reduction
2Adaptability or versatility
If the circuit input voltage range is increased to read out pixel signals in high-illumination environment, then the dynamic range is increased, but the circuit noise increases
Solution Approach 1:
The patent dynamically adjusts the W/L ratio of the constant current source transistor based on illumination conditions. In high-illumination environments, the W/L ratio is reduced to lower conversion efficiency, which prevents saturation and maintains a wide input voltage range. In low-illumination environments, the W/L ratio is increased to maximize conversion efficiency and minimize noise, thus adaptively optimizing both voltage range and noise performance
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
This approach allows for increased dynamic range without reducing the aperture ratio, effectively managing noise and voltage range across varying illumination environments.
Implementation Method 1
a pixel array section including a plurality of unit pixels each having a photoelectric conversion unit
Data Source
AI summary
A solid-state image sensor includes a pixel array section including a plurality of unit pixels each having a photoelectric conversion unit, the plurality of unit pixels being arranged in a matrix, a constant current source circuit unit having a constant current source connected to each of vertical signal lines provided in association with column arrangement of the pixel array section; and a control unit configured to control the constant current source circuit unit. The constant current source includes a plurality of transistors. The control unit switches, in a case where the plurality of transistors constituting the constant current source is regarded as one transistor having a gate width and a gate length being equivalent to each other, a ratio between the gate width and the gate length of the plurality of transistors on the basis of illumination in image-capturing environment.