SPAD Range-Gated Imaging With Phase-Shifted Recharge Timing
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Solution Overview
Problem
In range gate cameras using SPAD sensors, photons entering during the recharge period are not detected due to the short duration of the recharge period, leading to incomplete exposure and deteriorated image quality, especially in high-brightness environments.
Innovation Solution
An image capturing apparatus with a photoelectric conversion element that includes a counter, switch, and control unit to synchronize pulse light emission with exposure timing, using a clocked recharging method to ensure photon detection during both avalanche multiplication and recharge states, thereby enhancing image capture in high-brightness conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional passive recharging method is used in a SPAD sensor, then the sensor can operate in high-brightness environments, but photons incident during the recharge period are not detected, causing incomplete exposure and deteriorated image quality
Solution Approach 1:
The patent implements a clocked recharging method where the avalanche photodiode is periodically switched between avalanche multiplication mode and recharge mode using a clock signal. This periodic switching ensures that the photodiode is ready for photon detection at the appropriate timing during each exposure period, preventing missed detections while maintaining reliable operation in high-brightness environments.
Solution Approach 2:
The control unit performs preliminary actions by pre-charging the avalanche photodiode before the expected photon arrival time. The clock signal is advanced relative to the light emission timing, ensuring the photodiode is in the recharge state before photons arrive, thus preparing the sensor to detect photons without delay or loss.
2Productivity
If the recharge period is made shorter to improve frame rate, then productivity increases, but the probability of photons being incident during recharge increases, reducing detection accuracy
Solution Approach 1:
The patent dynamically adjusts the timing relationship between the clock signal and light emission by introducing a variable phase shift. The control unit can adjust the phase difference to optimize the balance between recharge time and detection time, allowing the system to adapt to different lighting conditions and maintain both high frame rate and accurate photon detection.
Solution Approach 2:
The control unit monitors the exposure period and adjusts the clock signal timing accordingly. By using feedback from the exposure timing information, the system can dynamically optimize the recharge phase to ensure maximum photon detection accuracy while maintaining high productivity.
3Measurement precision
If phase shift between clock signal and light emission is increased to ensure complete exposure, then measurement precision improves, but the complexity of timing control increases
Solution Approach 1:
The patent changes the timing parameter by introducing a phase shift between the clock signal and light emission. The control unit adjusts this phase shift parameter to optimize exposure completeness. By varying this single critical parameter, the system achieves complete exposure without requiring complex multi-parameter control mechanisms.
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
The solution allows for clear image capture of targeted distance ranges even under high-brightness conditions by synchronizing light emission and exposure timing, effectively addressing the issue of incomplete exposure in range gate cameras.
Implementation Method 1
an avalanche photodiode configured to generate pulses in response to photons incident thereon
Implementation Method 2
a photoelectric conversion element having a plurality of pixels, wherein the pixels each comprise a sensor unit comprising an avalanche photodiode configured to generate pulses in response to photons incident thereon
Data Source
AI summary
An image capturing apparatus comprises a photoelectric conversion element having a plurality of pixels, wherein each pixel comprises a sensor unit comprising an avalanche photodiode configured to generate pulses in response to photons incident thereon, a counter configured to count the number of the pulses, a memory configured to store count values of the counter, and a switch configured to switch the avalanche photodiode between a standby state in which avalanche multiplication is possible and a recharge state, a signal generation unit configured to supply a clock signal to the switch, a light emitting unit configured to perform pulse light emission for illuminating a subject in synchronization with the clock signal, and a control unit configured to perform a plurality of exposure operations by the counter according to timing of the pulse light emission and a predetermined image-capturing distance range for capturing images of a subject existing in the predetermined image-capturing distance range, and configured to shift relative timing of the clock signal and the pulse light emission by a predetermined phase for each predetermined exposure operation.