Image Sensor Readout Using Multi-Ramp ADC and Sample-and-Hold Isolation
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Solution Overview
Problem
Existing imaging technologies face challenges in achieving high image quality due to trade-offs between gradation increase and conversion speed, leading to noise generation and deteriorated image quality, particularly when increasing the number of pixels or using multiple comparators.
Innovation Solution
The proposed solution involves an imaging element with comparing units that compare analog signals with ramp waves of different inclinations, counters that output digital data, and a sample-and-hold unit that suppresses noise by electrically cutting the vertical signal line during comparisons, allowing for higher-gradation imaging without sacrificing frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple comparators are connected to one pixel vertical signal line to improve frame rate, then conversion speed is improved, but noise is generated due to kickback and image quality deteriorates
Solution Approach 1:
The patent divides the A/D conversion process into multiple segments by using multiple comparing units with different ramp wave inclinations. Each comparing unit handles a specific segment of the conversion process, allowing parallel operation that improves frame rate while the sample-and-hold unit isolates noise from each segment.
Solution Approach 2:
The sample-and-hold unit acts as an intermediary between the pixel vertical signal line and the comparing units. It holds the analog signal at a stable voltage level during comparison, preventing kickback noise from propagating back to the signal line while maintaining accurate comparison results.
2Measurement precision
If the number of pixels is increased to improve space resolution, then image quality is improved, but the number of pixels in output image decreases due to the connection method
Solution Approach 1:
The patent segments the comparison process into multiple independent comparing units that operate in parallel on the same vertical signal line. This allows full utilization of all pixel signals without loss, maintaining the number of pixels in the output image while improving conversion efficiency.
3Measurement precision
If a single ramp wave with moderate inclination is used to increase gradation, then output precision is improved, but conversion time increases and frame rate decreases
Solution Approach 1:
The patent segments the gradation measurement into multiple comparing units, each handling a portion of the total gradation range with optimized ramp wave inclinations. This allows parallel processing that achieves high precision gradation measurement without sacrificing frame rate.
Solution Approach 2:
The patent uses multiple comparing units with different ramp wave inclinations, where some units use steeper inclinations for faster conversion of certain signal ranges. This partial action approach allows the system to achieve high frame rates for all signals while maintaining high precision through the combination of multiple comparators.
Data Source
AI summary
An imaging apparatus according to the present disclosure includes a plurality of comparing units that compare analog signals supplied from pixels including photoelectric conversion elements through a vertical signal line with reference signals of ramp waves having different inclinations and output comparison results, a plurality of counters that execute counts until the comparison results are inverted for the different comparing units and output count values as digital data, and a sample-and-hold unit that electrically disconnects the vertical signal line and the comparing units and supplies the held analog signals to the comparing units while the comparing units execute the comparisons. The present disclosure can be applied to an imaging element, a control method, and an imaging apparatus.