CMOS Image Sensor Pixel Readout Timing for Blooming Control
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Solution Overview
Problem
In solid-state imaging devices, the technique of differentiating accumulation times between adjacent pixels to achieve a wide dynamic range is compromised by blooming, where optical charges from saturated pixels overflow and affect adjacent pixels with shorter accumulation times, leading to inaccurate signal processing.
Innovation Solution
The solution involves reading the signals from pixels with shorter accumulation times during the initial exposure period of pixels with longer accumulation times, ensuring that the reading operation is completed before overflow occurs, thus preventing signal interference from adjacent saturated pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pixels with different accumulation times are arranged adjacent to each other to achieve wide dynamic range, then signal sensitivity range is improved, but blooming occurs from saturated pixels affecting adjacent pixels
Solution Approach 1:
The patent applies preliminary action by reading out signals from pixels with shorter accumulation times during the initial exposure period, before saturation and blooming occur in pixels with longer accumulation times. This timing strategy prevents the harmful blooming effect from affecting the short-accumulation-time pixels, thereby resolving the contradiction between achieving wide dynamic range and preventing blooming interference.
2Measurement precision
If accumulation times are differentiated between adjacent pixels, then measurement precision is improved, but signal accuracy deteriorates due to blooming interference
Solution Approach 1:
The patent implements preliminary action by executing the readout operation for short-accumulation-time pixels during the beginning portion of the first accumulation time, before saturation occurs. This ensures that the proportional relationship between sensitivity and accumulation time is maintained, thereby preserving both measurement precision and signal accuracy without blooming interference.
3Quantity of substance
If long accumulation time pixels are saturated to capture high-sensitive signals, then dynamic range is expanded, but optical charge overflows into adjacent short accumulation time pixels
Solution Approach 1:
The patent applies preliminary action by completing the readout of short-accumulation-time pixel signals before the long-accumulation-time pixels become saturated. This timing arrangement ensures that even when optical charge overflows from saturated pixels, the short-accumulation-time pixels have already been read out and are not affected, thereby preventing charge overflow interference while maintaining expanded dynamic range.
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 effectively eliminates the adverse effects of blooming, maintaining the proportional relationship between sensitivity and accumulation time, thereby enhancing the accuracy of signal processing and achieving a wide dynamic range.
Implementation Method 1
pixels including photoelectric conversion elements are two-dimensionally arranged in a matrix
Data Source
AI summary
a CMOS image sensor including a pixel array unit having pixels arranged in even-numbered pixel rows and odd-numbered pixel rows. A reading operation performed such that a first signal of a first pixel group is read in a first accumulation time, and a second signal of a second pixel group is read in a second accumulation time shorter than said first accumulation time.