Pixel Circuit Adaptive Gain Selection for Image Sensor Dynamic Range
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Solution Overview
Problem
Image sensors face limitations in dynamic range due to the attenuation of incoming light by lenses and color filters, necessitating improved illumination and dynamic range solutions.
Innovation Solution
Implementing a pixel circuit with dual conversion gain (DCG) using analog-to-digital converters (ADCs) that selectively transmit high or low gain data based on predetermined thresholds, reducing power consumption and processing complexity by transmitting only one type of gain data at a time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lenses and color filters are used to illuminate photodiodes, then photodiode sensitivity can be optimized for specific wavelength ranges, but the incoming light is attenuated and dynamic range is limited
Solution Approach 1:
The pixel array is divided into two distinct sub-arrays: a first sub-array with photodiodes optimized for visible light wavelengths and a second sub-array with photodiodes optimized for infrared wavelengths. This segmentation allows each sub-array to capture light in its optimal wavelength range without the need for wavelength-selective filters, thereby reducing light attenuation and improving overall dynamic range.
2Reliability
If both high gain and low gain data are transmitted from ADCs, then complete image data is captured, but power consumption and processing complexity increase
Solution Approach 1:
The system dynamically selects which ADC output data to transmit based on real-time scene brightness conditions. A judge circuit determines whether the scene is bright or dark and selectively enables transmission of either high gain data or low gain data. This dynamic adaptation ensures complete image data capture while minimizing power consumption by transmitting only the necessary data type.
Solution Approach 2:
The system changes the gain parameter of the ADC based on scene conditions. In bright scenes, low gain mode is used; in dark scenes, high gain mode is used. This parameter change allows the system to capture complete image data across varying lighting conditions while reducing power consumption by avoiding simultaneous operation of both high gain and low gain ADC paths.
3Adaptability or versatility
If processing circuits are added to each pixel to improve functionality, then image processing capability increases, but circuit complexity and manufacturing difficulty increase
Solution Approach 1:
Rather than adding complex processing circuits to each individual pixel, the patent segments the pixel array into two specialized sub-arrays with different photodiode optimizations. This segmentation provides enhanced image processing capability for different wavelength ranges without increasing per-pixel circuit complexity, as each pixel remains relatively simple while the system as a whole gains versatility.
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
Enhances image sensor performance by optimizing dynamic range and reducing power consumption and processing time, achieving up to 50% less power and time compared to conventional methods.
Implementation Method 1
An image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and in response generate corresponding electrical charge
Data Source
AI summary
A pixel circuit, including a pixel array comprising a plurality of pixels, a plurality of analog to digital converters (ADCs), where during a pixel data readout the plurality of ADCs is communicatively coupled to a respective pixel of the plurality of pixels to receive image data from the respective pixel of the plurality of pixels, a plurality of judge blocks, wherein each judge block is communicatively coupled to a respective ADC of the plurality of ADCs and wherein each judge block is configured to select and transmit gain data based on comparing an output of the respective ADC to a predetermined threshold for the respective ADC, and an image signal processor (ISP) configured to receive outputs from the plurality of ADCs, and combine the outputs of the plurality of ADCs to produce a combined converted value for the respective pixel.