Oversampled Image Sensor Conditional Readout
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Solution Overview
Problem
Current electronic image sensors face challenges in achieving high signal-to-noise ratio (SNR) and efficient power management while maintaining spatial resolution and low-light sensitivity, particularly in conditional-read operations where pixel read-out disrupts photodiode charge integration.
Innovation Solution
A modified 4-transistor pixel architecture with a non-destructive overthreshold detection mechanism enables conditional-read operations by dissociating the reset threshold from pixel sample generation, allowing for progressive read-out and voltage-binning of analog signals, which enhances low-light sensitivity and reduces power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conditional-read operations are implemented in conventional image sensors, then power consumption is reduced, but photodiode charge integration is disrupted
Solution Approach 1:
The pixel array is divided into multiple independently controllable banks, allowing selective read-out of specific regions without affecting others. This segmentation enables conditional-read operations in only the necessary portions of the sensor, reducing overall power consumption while preserving charge integration in inactive regions.
Solution Approach 2:
The system performs preliminary assessment of scene luminance characteristics before initiating read-out operations. By evaluating lighting conditions in advance, the sensor can determine which banks require read-out and which can remain in integration mode, thereby reducing power consumption without disrupting necessary charge integration.
2Measurement precision
If spatial resolution is maintained in image sensors, then image quality is preserved, but low-light sensitivity deteriorates
Solution Approach 1:
The sensor dynamically adjusts its operational mode based on scene luminance characteristics. In low-light conditions, the system switches to a mode that prioritizes sensitivity by reducing read-out frequency and utilizing accumulated charge across multiple frames, while maintaining spatial resolution through selective bank read-out and image processing techniques.
Solution Approach 2:
The system changes operational parameters such as read-out frequency, integration time, and bank selection based on detected luminance levels. By adjusting these parameters dynamically, the sensor optimizes the balance between spatial resolution and low-light sensitivity, ensuring high performance across varying lighting conditions.
3Measurement precision
If signal-to-noise ratio is improved through oversampling, then noise reduction is achieved, but power consumption increases
Solution Approach 1:
The pixel array is divided into multiple independently controllable banks, allowing selective read-out of specific regions. This segmentation enables oversampling to be applied only where needed based on scene luminance characteristics, achieving noise reduction in critical areas while minimizing power consumption across the entire sensor.
Solution Approach 2:
The system applies oversampling selectively rather than uniformly across all pixels. By performing multiple read-outs only in banks or regions where noise reduction is most beneficial (determined by luminance assessment), the system achieves improved signal-to-noise ratio where needed while avoiding the excessive power consumption that would result from universal oversampling.
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 improves SNR by enabling correlated double sampling without disrupting photodiode charge integration, while dynamically scaling power consumption and dynamic range based on scene luminance, thereby balancing motion-blur mitigation and noise reduction.
Implementation Method 1
a photodiode to integrate incident photons during a frame interval into an accumulated charge
Implementation Method 2
a capacitor coupled to the floating diffusion to hold a sample of the accumulated charge
Data Source
AI summary
In an integrated-circuit image sensor having a pixel array, a first subframe readout policy is selected from among a plurality of subframe readout policies, each of the subframe readout policies specifying a first number of subframes of image data to be readout from the pixel array for each output image frame and respective exposure durations for each of the first number of subframes of image data, wherein a shortest one of the exposure durations is uniform for each of the subframe readout policies. Each of the first number of subframes of image data is read out from the pixel array following the respective exposure durations thereof while applying a respective analog readout gain. The analog readout gain applied during readout of at least a first subframe of the first number of subframes is scaled according to a ratio of the shortest one of the exposure durations to the exposure duration of the first subframe.