SPAD TOF Mode Control for Far-Target Depth Sensing
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Solution Overview
Problem
Existing TOF sensors face challenges in accurately measuring distances of objects far away due to background noise (dark count) from the SPAD, which is not mitigated by environmental filters, and increasing laser power poses eye safety issues.
Innovation Solution
The depth sensing is performed in two stages: a 'far target detection' stage to determine if the object is near or far, followed by a 'control logic' stage that adjusts the SPAD sensor's operation mode based on this determination, reducing the influence of dark count noise by turning the sensor on only when expected reflections are likely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser power is increased to improve signal strength for far targets, then measurement precision is improved, but object-affected harmful factors worsen due to eye safety issues
Solution Approach 1:
The system performs a preliminary far target detection stage before the main depth sensing stage. During this preliminary stage, the SPAD sensor operates in a first operation mode with higher sensitivity to detect if the target is far away. Based on this preliminary detection, the system then adjusts the sensor operation mode for the main sensing stage, avoiding the need to continuously operate at high sensitivity and thus reducing dark count noise while maintaining safety
Solution Approach 2:
The SPAD sensor operates in different operation modes dynamically adjusted based on target distance. The system switches between a first operation mode (higher sensitivity, lower threshold) for far target detection and a second operation mode (lower sensitivity, higher threshold) for near target detection. This dynamic adaptation allows optimal performance for each scenario without compromising safety or accumulating excessive dark count noise
2Measurement precision
If SPAD sensor operates continuously to detect all reflected light, then measurement precision is improved, but use of energy worsens due to unnecessary operation during non-reflection periods
Solution Approach 1:
The depth sensing process is divided into periodic stages: a far target detection stage followed by a main depth sensing stage. During the far target detection stage, the sensor operates in the first operation mode. If no far target is detected, the system transitions to the second operation mode for the main sensing stage. This periodic switching reduces energy consumption by avoiding continuous operation in the high-sensitivity first mode, while maintaining detection accuracy through appropriate mode selection
Solution Approach 2:
The system performs a preliminary check (far target detection) before committing to the main sensing operation. This preliminary action determines whether the sensor should operate in the energy-intensive first mode or the more efficient second mode, thereby optimizing energy usage based on actual scene requirements rather than continuous high-power operation
3Measurement precision
If SPAD sensor operates in high sensitivity mode to detect far targets, then measurement precision is improved, but reliability worsens due to increased dark count noise influence
Solution Approach 1:
The system dynamically adjusts the SPAD sensor operation mode based on detected target characteristics. When a far target is detected during the preliminary stage, the system switches to the second operation mode for main sensing, which has lower sensitivity and is less susceptible to dark count noise. This dynamic adaptation maintains measurement precision for far targets while improving reliability by reducing noise susceptibility during the main sensing phase
Solution Approach 2:
The depth sensing process is segmented into two distinct stages: far target detection and main depth sensing. Each stage uses appropriately optimized sensor operation modes. The first mode is optimized for detecting far targets with low signal strength, while the second mode is optimized for reliable measurement with reduced dark count influence. This segmentation allows each stage to operate at optimal sensitivity without compromising overall system reliability
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 method allows accurate depth sensing regardless of object distance, reducing energy consumption and increasing accuracy for far targets by minimizing dark count noise.
Implementation Method 1
a single-photon avalanche diode (SPAD) sensing circuit, configured to: receive a reflected light reflected from an object; and output a SPAD output signal based on the reflected light
Implementation Method 2
Time-of-Flight (TOF) is a method for measuring the distance between a sensor and an object, based on the time difference between the emission of a signal and a return of the signal to the sensor after being reflected by an object
Data Source
AI summary
A time-of-flight (TOF) detecting device is provided herein. The TOF detecting device includes a single-photon avalanche diode (SPAD) sensing circuit and a processing circuit. The SPAD sensing circuit is configured to: receive a reflected light reflected from an object; and output a SPAD output signal based on the reflected light. The processing circuit is coupled to the SPAD sensor and configured to: determine that whether the object is a near target or a far target based on the SPAD output signal; in response to the object is the near target or the far target being determined, adjust a mode of the SPAD sensing circuit; and determine a distance between the object and the TOF detecting device based on the mode.