CMOS Image Sensor Column AD Converter Segmentation for Readout Speed
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing imaging elements face challenges in achieving fast readout of pixel signals while minimizing errors due to increased capacitance in column parallel AD converters, which can lead to errors in Correlated Double Sampling (CDS) values.
Innovation Solution
The implementation of a pixel area with a column AD signal processing section and a ramp signal generation section, where AD conversion is performed alternately and repeatedly, with the ramp signal being controlled to be supplied only to AD conversion sections that are actively converting pixel signals, reducing the overall capacitance load and minimizing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the number of column parallel AD converters is increased to achieve faster readout, then the readout speed is improved, but the total capacitance value increases causing more errors in CDS values
Solution Approach 1:
The patent divides the pixel columns into multiple groups, with each group connected to a separate AD converter. Instead of having all AD converters operate simultaneously, the system segments the conversion process into alternating phases where different groups of AD converters operate at different times. This segmentation reduces the simultaneous capacitance load on any single converter while maintaining overall fast readout through parallel processing of multiple groups.
Solution Approach 2:
The patent implements periodic action by alternating the operation of different AD converter groups in time-separated phases. During each phase, only specific AD converters are active while others are inactive, creating a periodic pattern of conversion operations. This periodic operation allows the ramp signal to be supplied only to active converters, reducing total capacitance effects and preventing timing errors in CDS values while achieving fast overall readout through the alternating parallel processing.
2Productivity
If AD conversion is performed in parallel for all pixels, then conversion speed is improved, but capacitance effects cause errors in CDS values due to varying determination timings
Solution Approach 1:
The patent segments the pixel columns into multiple groups, with each group processed by dedicated AD converters in alternating phases. This segmentation ensures that within each active phase, the ramp signal is supplied only to the currently active AD converters, synchronizing their operation and eliminating the timing variations that cause CDS errors, while still achieving high productivity through parallel processing of multiple groups.
Solution Approach 2:
The patent employs periodic action by alternating the activation of different AD converter groups. During each periodic phase, only specific converters are active and receive the ramp signal, ensuring synchronized operation and accurate CDS measurement for that group. This periodic pattern maintains measurement precision by preventing capacitance interference from inactive converters while achieving high conversion productivity through the alternating parallel operation of multiple groups.
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 enables faster AD conversion while maintaining low error rates, thereby enhancing the speed and accuracy of pixel signal readout.
Implementation Method 1
An imaging element has pixels that include PDs (photodiodes) that convert light into an electric current
Data Source
AI summary
The present technology relates to an imaging element, an imaging method, and a piece of electronic equipment that permit faster processing. A column AD signal processing section and a ramp signal generation section are provided. The column AD signal processing section has, for each pixel column, an AD conversion section. The plurality of pixels arranged in the same column are connected to the AD conversion section via a vertical signal line. In parallel with reset operation or signal transfer operation, the pixel signals output from the pixels connected via other vertical signal lines are converted from analog to digital form by the AD conversion section. The ramp signal is supplied to the AD conversion sections that perform AD conversion of the pixel signals and is not supplied to the AD conversion sections that do not perform AD conversion. The present technology is applicable, for example, to CMOS image sensors.