CMOS Image Sensor A/D Converter Variable Resolution Dynamic Range
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Solution Overview
Problem
Existing CMOS image sensors have a limited dynamic range and slow operation speed, making them unsuitable for high-speed applications such as in-car cameras.
Innovation Solution
The proposed solution involves an A/D converter configuration where the resolution is set lower on the high illuminance side and higher on the low illuminance side, allowing for increased dynamic range and reduced conversion time by adjusting the ramp wave generation circuit to increase the falling speed of the ramp wave signal, thereby enhancing operation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution is set uniformly high across all illuminance levels, then measurement precision is improved, but the dynamic range decreases and operation speed slows down
Solution Approach 1:
The patent applies local quality by setting different resolution levels for different illuminance ranges. Specifically, the A/D converter uses high resolution for low illuminance signals and low resolution for high illuminance signals, optimizing performance for each local condition rather than using a uniform resolution across all conditions.
Solution Approach 2:
The patent implements dynamics by making the resolution variable rather than fixed. The A/D converter dynamically adjusts its resolution based on the input signal level, switching between high and low resolution modes according to the illuminance conditions, thereby adapting to varying signal requirements.
2Measurement precision
If the resolution is set uniformly high across all illuminance levels, then measurement precision is improved, but operation speed decreases
Solution Approach 1:
The patent applies local quality by setting different resolution levels for different illuminance ranges. Specifically, the A/D converter uses high resolution for low illuminance signals and low resolution for high illuminance signals, optimizing performance for each local condition rather than using a uniform resolution across all conditions.
Solution Approach 2:
The patent implements dynamics by making the resolution variable rather than fixed. The A/D converter dynamically adjusts its resolution based on the input signal level, switching between high and low resolution modes according to the illuminance conditions, thereby adapting to varying signal requirements.
3Productivity
If the ramp wave falling speed is increased to reduce conversion time, then operation speed is improved, but measurement precision may deteriorate
Solution Approach 1:
The patent implements dynamics by making the resolution variable rather than fixed. The A/D converter dynamically adjusts its resolution based on the input signal level, switching between high and low resolution modes according to the illuminance conditions, thereby adapting to varying signal requirements.
Solution Approach 2:
The patent applies parameter changes by modifying the resolution parameter according to signal conditions. By changing the resolution parameter dynamically based on illuminance levels, the system optimizes both measurement precision and operation speed for different operating conditions.
Data Source
AI summary
A CMOS image sensor used as a solid-state image sensing device includes a pixel circuit for outputting a voltage of a level corresponding to the illuminance, and an A/D converter for converting an output voltage of the pixel circuit into a digital signal. The resolution on the low illuminance side is higher than the resolution on the high illuminance side in the A/D converter. Thus, the dynamic range can be increased and the operation speed can be increased, compared to the case in which the resolution is constant independent of the illuminance.