Column Comparator Timing in Image Sensors to Suppress Color Mixture
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Solution Overview
Problem
Existing photoelectric conversion devices, such as CMOS image sensors, face challenges in achieving high comparison accuracy due to variations in reset signal timings, which can propagate noise and affect AD-converted data, particularly in color mixture scenarios leading to image quality deterioration.
Innovation Solution
The implementation of a photoelectric conversion device with a control circuit that stepwise adjusts the threshold values of comparator circuits for different color pixels, minimizing color mixture by controlling the timing of reset signals to prevent simultaneous inversions and reduce kickback noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reset signals are provided simultaneously to multiple comparator circuits, then reset operation efficiency is improved, but variation of reset signals propagates between adjacent columns causing AD-converted data to change from correct values
Solution Approach 1:
The patent applies periodic action by providing reset signals to comparator circuits in sequential periods rather than simultaneously. Specifically, reset signals are provided to odd-numbered columns in one period and to even-numbered columns in another period, achieving both efficient reset operation and prevention of noise propagation that would occur with simultaneous resetting.
Solution Approach 2:
The patent segments the reset operation by dividing comparator circuits into different groups (odd columns and even columns) and applying reset signals to each group at different timings. This segmentation prevents variation of reset signals from propagating between adjacent columns while maintaining overall reset efficiency.
2Measurement precision
If reset timing is optimized to prevent variation propagation, then AD conversion accuracy is improved, but reset operation becomes more complex
Solution Approach 1:
The patent reduces control complexity by using periodic action with a simple two-period cycle: odd columns are reset in the first period, even columns in the second period. This regular periodic pattern is easier to control than arbitrary staggered timings while still achieving the goal of preventing variation propagation between adjacent columns.
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 enhances the comparison accuracy of comparator circuits, thereby improving image quality by suppressing color mixture and noise-related issues, leading to higher image fidelity.
Implementation Method 1
Each of a plurality of pixels arranged to form a plurality of columns outputs a pixel signal
Data Source
AI summary
A photoelectric conversion device includes pixels arranged to form columns, comparator circuits for respective columns, and a control circuit that controls the comparator circuits. Each comparator circuit includes a first comparator circuit connected to a first pixel of a first color, a second comparator circuit arranged on a column adjacent to the first comparator circuit and connected to a second pixel of a second color, and a third comparator circuit arranged on a column adjacent to the second comparator circuit and connected to a third pixel of the first color. Each comparator circuit compares a pixel signal on a corresponding column with a reference signal changing with time and outputs a comparison signal indicating a different level whether a difference between these signals is smaller or larger than a threshold. The control circuit controls the threshold to change stepwise in order of the first, third, and second comparator circuits.