Clipping Circuit in Ineffective Pixel Region for CMOS Image Sensors
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Solution Overview
Problem
CMOS image sensors face challenges with inversion video noise due to pixel output saturation under strong light, which is exacerbated by the limitations of existing clipping circuits that restrict design freedom and increase chip area, while also failing to effectively reduce voltage variations.
Innovation Solution
A solid-state imaging device with a clipping circuit arranged in an ineffective pixel region, capable of clipping pixel readout voltages, comprising a photo-electric conversion element, transfer element, floating diffusion, source-follower element, and reset element, allowing for reduced chip area and voltage reduction without compromising image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a clipping circuit is arranged corresponding to an effective pixel region, then inversion video noise is prevented, but chip area increases and design freedom is restricted
Solution Approach 1:
The clipping circuit is extracted from the effective pixel region and relocated to the ineffective pixel region (optical black region). This separation allows the clipping function to be preserved while eliminating the conflict with effective pixel area, as the clipping circuit now occupies space that would otherwise be unused.
Solution Approach 2:
The clipping circuit is moved from a two-dimensional arrangement within the effective pixel array to a different spatial dimension - the peripheral ineffective pixel region. This dimensional relocation resolves the area conflict by utilizing previously underutilized space around the main pixel array.
2Reliability
If a clipping circuit is arranged corresponding to an effective pixel region, then inversion video noise is prevented, but design freedom is restricted
Solution Approach 1:
By extracting the clipping circuit from the effective pixel region constraints, the design gains freedom in positioning and configuring the clipping circuit without affecting pixel performance. The clipping circuit can now be optimized independently in the ineffective pixel region.
3Reliability
If clipping voltage is determined considering variation among chips, then inversion video noise is prevented, but voltage reduction is compromised
Solution Approach 1:
The clipping circuit uses its own internal voltage reference and control mechanism to automatically clip pixel output voltages. This self-service approach eliminates the need for external voltage adjustment considering chip variations, as the clipping function inherently handles voltage limiting without requiring additional voltage headroom.
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
The solution effectively prevents inversion video noise and reduces chip area, enabling higher image quality by clipping pixel readout voltages and minimizing voltage variations, thus improving the performance of CMOS image sensors under high luminance conditions.
Implementation Method 1
a pixel portion in which pixels are arranged, each pixel including a photo-electric conversion element which accumulates a charge generated by photo-electric conversion
Data Source
AI summary
A solid-state imaging device capable of reducing an area of a chip, capable of realizing both reduction of voltage and prevention of inversion video noise and consequently capable of realizing a higher image quality having a pixel portion and a clipping circuit capable of clipping a pixel readout voltage in accordance with a clipping voltage, wherein the pixel includes a photo-electric conversion element PD, a transfer element capable of transferring a charge accumulated in the photo-electric conversion element in a transfer period, a floating diffusion FD to which the charge accumulated in the photo-electric conversion element is transferred through a transfer element, a source-follower element which converts the charge in the floating diffusion to a voltage signal in accordance with a charge quantity, and a reset element which resets the floating diffusion to a predetermined potential in a resetting period, and the clipping circuit is arranged in an ineffective region of the pixel portion, a driving method for the same, and an electronic apparatus.