Dual Ramp Signal AD Conversion for Noise Reduction
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Solution Overview
Problem
Existing imaging apparatuses face challenges in reducing random noise during AD conversion operations, with techniques like Japanese Patent Laid-Open No. 2010-103913 requiring equal periods for multiple AD conversions, leading to increased time, and Japanese Patent Laid-Open No. 2010-252140 struggling to reduce noise due to arbitrary voltage offsets.
Innovation Solution
The proposed imaging apparatus employs a dual ramp signal approach, where a first ramp signal with a smaller amplitude range is compared with an optical signal, and a second ramp signal with a larger amplitude range is used for subsequent comparisons, allowing for reduced random noise and shorter AD conversion periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple AD conversions are performed using the same ramp signal with equal periods, then noise characteristics are improved, but the conversion time increases
Solution Approach 1:
The patent performs multiple AD conversions using periodic ramp signals with different amplitudes. By alternating between a first ramp signal (smaller amplitude) and a second ramp signal (larger amplitude) in periodic fashion, the system achieves both noise reduction through multiple conversions and time efficiency through overlapping operation periods.
Solution Approach 2:
The patent starts the first AD conversion using the first ramp signal before the second AD conversion using the second ramp signal is completed. This preliminary action allows the conversions to overlap in time, reducing the total conversion time while still achieving noise reduction through multiple measurements.
2Productivity
If multiple AD conversions are performed using ramp signals with different amplitudes and voltage offsets, then reading time is reduced and bit accuracy is improved, but noise reduction capability deteriorates
Solution Approach 1:
The patent applies different ramp signal characteristics to different conversion operations: the first ramp signal uses smaller amplitude for precise measurements, while the second ramp signal uses larger amplitude for faster conversions. This local differentiation optimizes each conversion for its specific purpose while maintaining overall system efficiency.
Solution Approach 2:
The patent changes the amplitude parameter of the ramp signal between conversions rather than using fixed voltage offsets. By alternating between smaller and larger amplitudes, the system achieves both fast reading times and effective noise reduction without the limitations of arbitrary voltage offsets.
3Speed
If the first comparison is performed in parallel with the second comparison, then conversion speed is improved, but measurement accuracy may deteriorate
Solution Approach 1:
The patent maintains continuous useful action by overlapping the first and second AD conversions. The first conversion starts before the second conversion ends, ensuring that the imaging apparatus continuously processes signals without idle time, thereby improving conversion speed while maintaining accuracy through the use of appropriate ramp signals for each conversion.
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 method effectively reduces random noise in digital signals while minimizing the time required for AD conversion operations, improving noise characteristics and efficiency compared to previous techniques.
Implementation Method 1
pixels which generate optical signals by performing photoelectric conversion on light and output the optical signals
Data Source
AI summary
A first ramp signal having a potential which is changed with time in a first amplitude range in a first period and a second ramp signal in which a potential is changed with time in a second amplitude range which includes the first amplitude range and which has maximum amplitude larger than maximum amplitude of the first amplitude range and an amount of the change of the potential per unit time is the same as an amount of the change of the potential per unit time of the first ramp signal are generated, and comparison between an optical signal and the first ramp signal and comparison between the optical signal and the second ramp signal are performed in parallel.