CMOS Image Sensor Differential Processing for Power Reduction
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Solution Overview
Problem
CMOS image sensors face challenges in reducing power consumption while effectively detecting motion between frames, which is crucial for mobile devices where energy efficiency is paramount.
Innovation Solution
The method involves storing differences between analog pixel signals from previous and current frames as one-bit digital signals, using a pixel array with a pixel signal difference storage circuit and an analog-to-digital conversion circuit that includes comparators and coupling capacitors to convert these differences into one-bit digital signals, and a power management unit to control power usage based on the operating mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image sensor processes and outputs full-resolution analog pixel signals from all pixels, then the image quality and detail information are maintained, but the power consumption increases significantly
Solution Approach 1:
The pixel array is divided into multiple regions including a first region for full-resolution imaging and a second region for motion detection. Each region processes signals independently, allowing the system to maintain high image quality in the first region while reducing power consumption through differential processing in the second region.
Solution Approach 2:
Instead of processing all pixel signals at full resolution, the patent applies differential processing (comparing current frame with previous frame) only to specific regions where motion detection is needed. This partial processing approach maintains necessary image quality while significantly reducing the computational load and power consumption.
2Use of energy by moving object
If the image sensor uses differential processing to detect motion between frames, then power consumption is reduced, but the complexity of the circuit increases
Solution Approach 1:
The patent combines the differential processing circuitry with the existing pixel array and readout circuitry. The coupling capacitors are integrated into the pixel structure, and the differential comparison is performed within the same signal path, reducing overall system complexity despite adding motion detection functionality.
Solution Approach 2:
Coupling capacitors are used as intermediary elements to store and transfer the differential signal between the pixel and the readout circuit. This intermediary approach simplifies the differential processing by using passive components rather than active circuitry, reducing the overall circuit complexity.
3Loss of information
If the image sensor activates all pixels for every frame capture, then complete image data is captured, but the power consumption increases
Solution Approach 1:
The pixel array is segmented into a first region for full-resolution imaging and a second region for motion detection. This segmentation allows the system to capture complete image data in the first region while using energy-efficient differential processing in the second region, reducing overall power consumption.
Solution Approach 2:
The pixel array serves multiple functions: full-resolution imaging in the first region and motion detection in the second region. This multi-functionality allows the same hardware to achieve both complete image data capture and power reduction through selective processing modes.
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 reduces power consumption by selectively activating only necessary components during motion sensing, enhancing energy efficiency while accurately detecting frame differences for motion detection.
Implementation Method 1
a pixel signal difference storage circuit storing each difference between each of a plurality of first analog pixel signals which are output from the plurality of pixels and correspond to a previous frame and each of a plurality of second analog pixel signals which are output from the plurality of pixels and correspond to a current frame
Implementation Method 2
the analog to digital conversion circuit includes a plurality of comparators, each of the plurality of comparators compares each of the stored differences and a reference voltage, and output each of the plurality of one-bit digital signals according to the results of the comparison
Implementation Method 3
each of the first analog pixel signals may correspond to an amount of charge of photo charges accumulated in each of the plurality of pixels during the previous frame
Data Source
AI summary
A method of operating an image processing system includes storing differences between first analog pixel signals and second analog pixel signals and converting the stored differences to one-bit digital signals, the first analog pixel signals being output from a plurality of pixels and corresponding to a previous frame, and the second analog pixel signals being output from the plurality of pixels and corresponding to a current frame.