Image Sensor Bias Circuit Reduces Channel Variation
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Solution Overview
Problem
Channel variation between colors occurs in CMOS image sensors during sub-sampling, leading to degraded image quality due to inter-column capacitive coupling when pixel outputs of skipped columns float.
Innovation Solution
Incorporating bias circuits connected to column lines of non-selected pixels to fix their voltage to a bias voltage, preventing floating and reducing channel variation, while switches control the selection of column lines to manage pixel signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sub-sampling is used to decrease power consumption and increase frame rate, then power consumption is reduced and frame rate increases, but channel variation between colors occurs due to floating pixel outputs
Solution Approach 1:
The bias circuit applies a preliminary counteracting voltage to the column line of non-selected pixels before the floating condition can cause channel variation. This preemptive action prevents the capacitive coupling effect from manifesting by maintaining the column line voltage at a stable bias level throughout the sub-sampling operation.
2Loss of energy
If pixel current source is controlled off for skipped columns to decrease power consumption, then power consumption decreases, but pixel outputs float causing channel variation
Solution Approach 1:
The bias circuit acts as an intermediary element between the pixel current source and the column line. When the pixel current source is turned off for non-selected columns, the bias circuit mediates by providing a stable voltage reference through the column line, preventing the floating condition while allowing the current source to remain off for power savings.
3Productivity
If inter-column capacitive coupling occurs in sub-sampling mode, then frame rate increases, but channel variation between adjacent pixel columns occurs
Solution Approach 1:
The bias circuit establishes equipotential conditions on the column lines of non-selected pixels by maintaining them at a constant bias voltage. This prevents potential differences from developing between adjacent columns due to capacitive coupling, thereby eliminating channel variation while allowing the sub-sampling operation to proceed at high frame rates.
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 effectively minimizes channel variation between colors, enhancing image quality by stabilizing voltages and reducing power consumption in live-view modes, thereby improving the frame rate and image sensor performance.
Implementation Method 1
each unit pixel comprising a photoelectric conversion unit configured to generate a pixel signal in response to incident light
Data Source
AI summary
An image sensor for reducing channel variation and an image processing system including the same. The image sensor includes first to mth pixels (m≧2), each of which is connected to a corresponding column line from among first to mth column lines and is configured to output a respective pixel signal.’ The image sensor further includes first to mth bias circuits, each of which is connected to a corresponding column line from among the first to mth column lines and is configured to fix a voltage of the corresponding column line to a bias voltage when a column line-specific pixel is not selected to output the respective pixel signal. An analog-to-digital converter in the image sensor is configured to convert the pixel signals into digital signals.