Column ADC Resolution Correction for Image Sensor Linearity
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Solution Overview
Problem
Existing image pickup apparatuses face challenges in maintaining linearity between analog and digital signals due to variations in digital-to-analog converter characteristics, leading to inconsistencies in the slopes of reference signals used for analog-to-digital conversion.
Innovation Solution
The proposed solution involves a photoelectric conversion apparatus with a configuration that includes a pixel unit, a vertical scanning circuit, an amplifier unit, a ramp signal generation circuit, a comparator unit, a counter unit, and a memory unit, which generates and compares ramp signals with different slopes to achieve high-resolution analog-to-digital conversion by correcting the ratio between resolutions and performing bit shift operations to obtain high-precision data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple comparators with reference signals of different slopes are used for analog-to-digital conversion, then bit precision is improved, but linearity between analog and digital signals deteriorates due to variations in DAC characteristics
Solution Approach 1:
The patent introduces a feedback mechanism where the digital output from the comparator unit is fed back to the DAC unit. This feedback loop allows the system to detect and correct deviations in the reference signal slopes caused by DAC variations, thereby maintaining linearity between analog and digital signals while preserving high bit precision through multiple comparators
Solution Approach 2:
The patent introduces a correction unit as an intermediary between the comparator unit and the output. This correction unit processes the digital signals from multiple comparators and applies corrections based on the detected slope differences, serving as a mediator that maintains linearity while allowing the use of multiple comparators for high precision conversion
2Measurement precision
If reference signal slopes are set to exponential multiples for high precision conversion, then bit precision is improved, but manufacturing precision deteriorates due to difficulty in maintaining exact slope ratios
Solution Approach 1:
The patent changes the approach from physically setting exact exponential slope ratios to dynamically adjusting slope parameters through digital correction. The system uses digital processing to compensate for manufacturing variations in slope ratios, allowing exponential multiple relationships to be maintained in software rather than relying on precise physical implementation
Solution Approach 2:
The feedback mechanism detects actual slope ratios and applies corrections to maintain the desired exponential multiple relationships. This allows the system to achieve precise slope relationships through control rather than manufacturing, improving both bit precision and reducing manufacturing precision requirements
3Ease of manufacture
If DAC variations are allowed for ease of manufacture, then ease of manufacture is improved, but measurement precision deteriorates due to slope differences affecting linearity
Solution Approach 1:
The feedback loop continuously monitors the actual reference signal slopes generated by the DAC and applies real-time corrections to compensate for variations. This allows the system to tolerate DAC manufacturing variations while maintaining high measurement precision and linearity through active correction
Solution Approach 2:
The correction unit acts as an intermediary that decouples manufacturing precision from measurement precision. It accepts inputs from DACs with varying slopes and produces corrected outputs with consistent linearity, allowing easy manufacture of DACs while maintaining high measurement precision
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 ensures high-precision analog-to-digital conversion by maintaining linearity between analog and digital signals, reducing noise influence and achieving accurate bit precision, even in varying environmental conditions.
Implementation Method 1
a photoelectric conversion apparatus (100) performs photoelectric conversion on a received optical image
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3C
AI summary
A photoelectric conversion apparatus (100) includes a plurality of pixels (10-1) provided in a plurality of columns, a plurality of analog-to-digital conversion units (30, 40, 30-1, 40-1) each provided for a corresponding one of the plurality of columns, and a correction unit (50, 40-1). Each of the plurality of analog-to-digital conversion units (30, 40, 30-1, 40-1) is configured to convert a signal of a corresponding one of the plurality of pixels (10-1) into a digital signal at a resolution corresponding to a magnitude of the signal. The correction unit (50, 40-1) is configured to correct a difference in the resolution.