SPAD Image Sensor Overflow Timing for Low-Power Photon Counting
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Solution Overview
Problem
Single-photon avalanche diodes (SPADs) face increased power consumption due to the use of large bit counters for photon counting, which is inefficient and consumes significant power.
Innovation Solution
The method estimates the total number of photons by utilizing the overflow time point of a counter, reducing power consumption by counting only a portion of the total photons received.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a counter with a large number of bits is used to count a large number of photons, then the measurement precision is improved, but the use of energy increases
Solution Approach 1:
The patent applies partial action by counting only a portion of total photons received during exposure time rather than counting all photons. The counter operates for a limited duration until it reaches an overflow state, at which point the remaining exposure time is used to estimate the total photon count. This partial counting approach reduces the operational time and energy consumption of the counter while still providing sufficient measurement precision through mathematical estimation.
Solution Approach 2:
The patent changes the parameter of counting duration from the full exposure time to a limited portion of exposure time. By modifying the time parameter at which the counter stops operating (based on overflow conditions), the system achieves lower power consumption while maintaining measurement accuracy through extrapolation of the total photon count based on the counted portion and the remaining exposure time.
2Measurement precision
If the counter counts all photons during the entire exposure time, then the measurement precision is improved, but the duration of action of the counter increases
Solution Approach 1:
The counter operates partially during the exposure period, stopping when it reaches an overflow state. Instead of continuously counting all photons throughout the entire exposure time, the counter performs counting for only a portion of the exposure duration. The remaining photon count is estimated using the overflow time point and exposure time relationship, thereby reducing the actual duration of counter operation while maintaining measurement precision.
Solution Approach 2:
The system performs preliminary counting action until the counter overflows, which provides sufficient information to estimate the total photon count. By stopping the counter operation after this preliminary phase (when overflow occurs), the system avoids unnecessary continued counting and reduces the overall duration of counter action while still achieving accurate total photon measurement through estimation.
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
Significantly reduces power consumption while maintaining image quality by estimating the total photon count through the counter overflow time, allowing for efficient operation under various illumination conditions.
Implementation Method 1
the single-photon avalanche diode has very high sensitivity because it uses avalanche multiplication to amplify a single incident photon
Data Source
AI summary
According to an embodiment of the present disclosure, a single-photon avalanche diode-based image sensor may comprise: a single-photon avalanche diode (SPAD) which generates a plurality of pulses corresponding to a plurality of photons, received during a predetermined exposure time, respectively; a front-end circuit which receives a set of pulses received during a partial time of the exposure time among the plurality of pulses; a counter which counts the number of pulses in the set of pulses; and a global clock which provides a plurality of clock pulses to the front-end circuit from after the partial time, wherein the quality of an image acquired using the SPAD is determined based on the timing of the global clock.