Image Sensor A/D Conversion with Mode-Based Offset and Gain Correction
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Solution Overview
Problem
Existing image pickup apparatuses face challenges in achieving high-speed multi-bit A/D conversion while maintaining accurate input/output characteristics, particularly due to the ramp A/D conversion method which prolongs conversion time and introduces shifts in characteristics when switching between ramp signals based on signal amplitude.
Innovation Solution
An image pickup apparatus that includes a pixel for converting optical signals into electrical signals, a comparison unit for comparing pixel signals with a reference voltage, an A/D conversion unit for selected conversion modes, and a correction unit to adjust offset and gain, allowing for offset or gain correction based on the selected mode to align input/output characteristics with ideal values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ramp A/D conversion method is used to perform multi-bit conversion, then conversion precision is improved, but conversion time is significantly prolonged
Solution Approach 1:
The patent segments the A/D conversion process into multiple stages: first performing 10-bit conversion, then conditionally performing additional 2-bit conversion based on signal amplitude. This segmentation allows the system to achieve high precision when needed while maintaining fast conversion speed for most cases, resolving the contradiction between conversion precision and conversion time.
Solution Approach 2:
The patent dynamically adjusts the conversion bit depth based on the signal amplitude characteristics. When the signal amplitude is small (within ±2.5V), additional 2-bit conversion is performed to enhance precision. When the amplitude is large, only 10-bit conversion is performed for faster processing. This dynamic adaptation resolves the time-precision tradeoff.
2Productivity
If switching between different ramp signals based on signal amplitude is performed, then conversion speed is improved, but input/output characteristics shift occurs
Solution Approach 1:
The patent performs preliminary 10-bit A/D conversion before deciding whether to perform additional 2-bit conversion. This preliminary action establishes a baseline conversion result that can be subsequently refined. By having this initial conversion in place, the system can quickly determine the signal amplitude range and apply appropriate correction without requiring complete re-conversion, thus maintaining both speed and accuracy.
Solution Approach 2:
The patent uses feedback from the first A/D conversion result to control the second A/D conversion process. The output of the first conversion informs whether additional conversion is needed and how to interpret the second conversion results. This feedback mechanism ensures that the combined conversion process maintains accurate input/output characteristics while achieving high conversion speed.
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 enables high-speed multi-bit A/D conversion with improved image quality by correcting shifts in input/output characteristics, preventing prolonged conversion times and maintaining accurate data representation.
Implementation Method 1
a pixel configured to convert optical signal into an electrical signal
Data Source
AI summary
An image pickup apparatus comprising a pixel configured to convert optical signal into an electrical signal, a comparison unit configured to compare a pixel signal from the pixel with a reference voltage, an A/D conversion unit configured to analog/digital (A/D)-convert the pixel signal in a conversion mode selected based on a comparison result of the comparison unit, and a correction unit configured to correct at least one of an offset and a gain generated by the A/D conversion for an output data of the A/D conversion unit, wherein a value for offset correction or gain correction performed by the correction unit is changed according to the selected conversion mode.