Focus Detection Apparatus Inhibiting AD Converter Level Differences
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Solution Overview
Problem
Conventional auto-focus systems face errors in focus detection due to discontinuous output among nearby pixels caused by column amplifier gain and offset errors, especially when the amount of incident light is around the threshold for switching gain settings.
Innovation Solution
A focus detection apparatus with an image sensor and an AD converter that switches between low-luminance and high-luminance conversion modes, featuring a determination unit to assess the output signal and an inhibition unit to prevent level differences at the mode boundary, allowing for accurate defocus calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If column amplifier gain switching is performed in accordance with light amount for each pixel, then dynamic range is enlarged and AF control becomes independent of subject contrast, but output discontinuity occurs among nearby pixels at the gain switching boundary due to gain and offset errors
Solution Approach 1:
The patent introduces an intermediary processing step between the column amplifier output and the final focus detection calculation. A correction unit is inserted that detects and corrects offset errors in the column amplifiers, particularly at the gain switching boundary. This intermediary correction mechanism eliminates the discontinuity caused by gain switching while preserving the extended dynamic range benefit.
Solution Approach 2:
The patent implements a feedback mechanism where the system monitors the output signals from multiple pixels and detects discontinuities at gain switching boundaries. When such discontinuities are detected, the system applies corrective feedback to compensate for the offset errors, ensuring continuous and accurate focus detection across the entire pixel array regardless of brightness variations.
2Adaptability or versatility
If gain switching is performed at pixel level, then each pixel can optimize for its light amount, but complexity of the AD conversion system increases due to need for coordinated gain management across multiple pixels
Solution Approach 1:
The patent merges the gain control functionality into a centralized column amplifier structure rather than implementing independent gain control in each pixel. By combining the gain switching operation at the column level and implementing a unified correction mechanism, the system achieves pixel-level adaptability to different brightness conditions while avoiding the complexity of distributed gain management across individual pixels.
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
Enables highly accurate auto-focus control independent of subject brightness by inhibiting level differences and ensuring consistent AD conversion, thereby reducing errors in focus detection.
Implementation Method 1
an image sensor having a plurality of pixels that receive light from a subject that passes through an imaging lens
Data Source
AI summary
A focus detection apparatus includes an image sensor having a plurality of pixels and an AD converter configured to switch a low-luminance conversion mode and a high-luminance conversion mode, a determination unit configured to determine whether an output signal is a signal AD converted in both the low-luminance conversion mode and the high-luminance conversion mode or a signal AD converted in only one of the two modes, an inhibition unit configured to, in a case where the output signal from the AD converter is a signal AD converted in both the two modes, inhibit a level difference of the output signal at a boundary between the two modes, and a calculation unit configured to, based on the signal for which the level difference is inhibited, calculate an amount of defocus of the imaging lens.