Three-Layer Stacked Image Sensor Reducing Comparator Noise
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Solution Overview
Problem
In solid-state image capturing devices with a two-layer stacked structure, the comparator becomes small in size, leading to degraded noise performance.
Innovation Solution
A solid-state image capturing device with a three-layer stacked structure, where each pixel block includes a photoelectric conversion unit, a transfer transistor, a floating diffusion, and a shared comparator on one substrate, a code generation circuit, a storage unit, and a timing control circuit on another, allowing for efficient signal processing and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a two-layer stacked structure is used, then the device complexity is reduced, but the comparator size becomes small and noise performance is degraded
Solution Approach 1:
The patent transitions from a two-layer stacked structure to a three-layer stacked structure, adding a new dimension (layer) to the device architecture. This allows the comparator to be placed on a dedicated third substrate, increasing its effective size and improving noise performance while maintaining the benefits of stacked structure integration.
2Productivity
If multiple comparators are provided for multiple pixels, then the signal processing capability is improved, but the device area increases
Solution Approach 1:
The patent implements a shared comparator architecture where a single comparator on the third substrate serves multiple pixel blocks. This multi-functional approach allows one comparator to process signals from multiple pixels sequentially, maintaining high signal processing capability while minimizing the number of comparators needed and reducing overall device area.
Solution Approach 2:
The patent combines multiple pixel blocks into groups that share common comparators. By merging the functionality of multiple comparators into a single shared resource that operates across different time periods, the device achieves efficient signal processing without requiring proportionally more comparator units, thus reducing the overall device area.
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 three-layer structure enables reduced comparator noise and improved signal processing, enhancing the overall noise performance of the device.
Implementation Method 1
a photoelectric conversion unit that generates electric charges according to incident light
Data Source
AI summary
An AD conversion circuit with reduced comparator noise is disclosed. In one example, a solid-state image capturing device includes at least three stacked substrates, in which for each pixel block, a first substrate includes a photoelectric conversion unit that generates electric charges according to incident light, a transfer transistor, and a floating diffusion, a second substrate includes one comparator that compares a signal according to a voltage of the floating diffusion with a reference signal, a third substrate includes a code generation circuit that generates a code of a counter, a storage unit that stores the code, and a timing control circuit that controls a timing of storing the code in the storage unit, and the solid-state image capturing device further includes a pixel array in which a plurality of the pixel blocks is arranged.