SPAD Range-Gated Imaging With Clocked Recharge Timing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In range gate cameras using SPAD sensors, the recharge period during high brightness conditions results in undetected photons, leading to reduced image quality due to missed exposure of reflected light from specific distance ranges.
Innovation Solution
An image capturing apparatus with a photoelectric conversion element featuring avalanche photodiodes, a counter, memory, and a switch that employs a clocked recharging method to synchronize light emission and exposure timing, allowing for continuous photon detection even during high illuminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional passive recharging method is used in SPAD sensors, then the sensor can operate under high brightness conditions, but photons incident during the recharge period are not detected, causing image quality deterioration
Solution Approach 1:
The patent implements a clocked recharging method where the avalanche photodiode is periodically switched between a first state (for photon detection) and a second state (for recharging) using a clock signal. This periodic switching ensures that the photodiode alternates between detecting photons and recharging, preventing missed detections during recharge periods while maintaining operation under high brightness conditions.
Solution Approach 2:
The patent uses a feedback mechanism where the output signal from the avalanche photodiode is fed back to control the switching between detection and recharge states. The feedback signal, combined with the clock signal, controls the switch to ensure proper timing of photon detection versus recharging, thereby maintaining detection accuracy even when photons incident during recharge periods would otherwise be missed.
2Measurement precision
If the recharge period is extended to ensure complete photon detection, then measurement precision improves, but the exposure period for reflected light from specific distance ranges is reduced or lost
Solution Approach 1:
The patent employs periodic switching between detection and recharge states with precise timing control. By using clock signals to synchronize the switching timing with the light emission timing, the system ensures that the photodiode is in the detection state during the critical exposure period for reflected light from target distance ranges, while still allowing adequate recharge time between cycles.
Solution Approach 2:
The patent performs preliminary recharging of the avalanche photodiode before the expected arrival of reflected light from the target distance range. By pre-recharging the photodiode in advance and using clock signals to timing the detection window, the system ensures the photodiode is ready to detect photons when they arrive, while maintaining sufficient exposure time for the target range.
3Measurement precision
If a clocked recharging method is used to detect photons during recharge periods, then photon detection accuracy improves, but the complexity of the control circuit increases
Solution Approach 1:
The patent uses a multi-functional switch that serves both as a control element for the avalanche photodiode's detection/recharge states and as a timing synchronization element with the light emission system. The same switch and clock signal mechanism that enables precise photon detection timing also coordinates with the light emission timing, reducing the need for separate control circuits.
Solution Approach 2:
The patent employs feedback from the avalanche photodiode's output signal to control the switching timing, which simplifies the control circuit by using the photodiode's own signal to trigger the appropriate state changes. This feedback mechanism eliminates the need for complex external timing circuits, as the photodiode's output naturally provides the timing reference needed for synchronized operation.
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
Enables clear image capture of targeted distance ranges even under high brightness conditions by ensuring all photon events are counted, improving image quality by synchronizing light emission and exposure periods.
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
Data Source
Figure 1
Figure 2
Figure 3
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.