SPAD Image Sensor Asynchronous Resetting for Low-Power HDR Sensing
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Solution Overview
Problem
Conventional image sensors face challenges in achieving a high signal-to-noise ratio over an extended dynamic range while maintaining low power consumption, primarily due to high power consumption and data rate associated with pixel switching and data reading.
Innovation Solution
The image sensor employs an asynchronous operation of photodetector elements with increased dead time, allowing asynchronous resetting and recharging of photodiodes after photon detection, which reduces pixel activity and operates in a non-linear regime, enabling data compression and lower power consumption without degrading the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional synchronous pixel resetting and data reading is used, then complete photon detection coverage is achieved, but power consumption and data rate increase significantly
Solution Approach 1:
The patent transitions from synchronous to asynchronous pixel resetting, where each pixel is reset dynamically based on its individual photon detection events rather than following a global clock signal. This dynamic approach allows pixels to remain inactive during periods without photon events, reducing overall power consumption while maintaining complete detection coverage.
Solution Approach 2:
Each pixel operates autonomously with self-triggered resetting based on its own photon detection events. The pixel automatically resets after detecting photons without requiring external synchronous control signals, enabling independent operation that reduces system-wide power consumption and data transmission requirements.
2Measurement precision
If dead time is minimized to increase maximum counting rate, then Poisson-limited signal-to-noise ratio is achieved, but power consumption increases due to frequent pixel switching
Solution Approach 1:
The patent optimizes the dead time parameter to a specific value that balances signal-to-noise ratio and power consumption. By carefully selecting the dead time duration, the system achieves acceptable measurement precision while significantly reducing the frequency of pixel switching operations, thereby lowering power consumption.
3Use of energy by moving object
If asynchronous operation with increased dead time is used, then power consumption and data rate are reduced, but reading speed may be affected
Solution Approach 1:
The asynchronous operation ensures continuous photon detection across all pixels without synchronization gaps. While individual pixels have extended dead times, the overall system maintains continuous detection capability because different pixels are at different stages of their detection cycles, preserving effective reading speed while reducing power consumption.
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 results in reduced power consumption and output data rate, allowing high-speed reading with maintained signal-to-noise ratio, and enables a broader operation range across various light intensities, achieving a high dynamic range with digital pixel intensity provided directly by each photodetector cell.
Implementation Method 1
a single-photon avalanche diode (SPAD) which is configured to detect light and amplify an electron-hole pair through an electrical field which produces a detectable avalanche of electrons upon photodetection
Implementation Method 2
each electron-hole pair can trigger an avalanche multiplication process forming a photon detection signal as an electrical pulse signal
Data Source
AI summary
The invention relates to an image sensor comprising a photodetector array including neighboring photodetector elements, each photodetector element comprising: —a photodetector cell having a photodiode and a reset unit; —a cell control unit coupled with the photodetector cell and configured to reset the photodiode by means of the reset unit; wherein the cell control unit is configured to asynchronously effect resetting of the photodiode after a given dead time after detection of a photon.