SPAD Counter Distribution for Multi-Phase ToF Ranging
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Solution Overview
Problem
The indirect Time of Flight (ToF) ranging method is inefficient due to the need for sequential emission and reception of light source light and reflection light at multiple phases, which limits its efficiency in measuring distance.
Innovation Solution
A light receiving device with a single photon avalanche diode (SPAD) that uses avalanche multiplication to detect photons, a current source for recharge, and a distribution section to select target counters for pulse signal processing, allowing parallel measurement across multiple phases based on control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential emission and reception of light source light and reflection light is performed for each phase, then phase difference measurement can be achieved, but ranging efficiency deteriorates
Solution Approach 1:
The measurement period is divided into multiple phases (first phase, second phase, third phase, fourth phase), with each phase having dedicated emission and reception time periods. This segmentation allows systematic measurement of phase differences across multiple intervals, improving measurement accuracy while maintaining efficient operation through structured parallel processing.
Solution Approach 2:
The light source light is emitted periodically at different phases (0°, 90°, 180°, 270°) in a cyclic manner, with each phase having its own emission and reception time periods. This periodic action enables continuous measurement across multiple cycles, improving both measurement precision and overall ranging efficiency by utilizing every time period effectively.
2Measurement precision
If multiple phases are measured sequentially, then comprehensive phase difference data can be obtained, but measurement time increases
Solution Approach 1:
The measurement process operates continuously without idle periods between phases. Each phase's emission and reception time periods are back-to-back, with the light source light emitted periodically without interruption. This continuous operation reduces total measurement time while maintaining comprehensive phase difference data collection across all four phases.
Solution Approach 2:
By implementing periodic emission and reception at four different phases within a single measurement period, the system obtains comprehensive phase difference data faster than sequential measurement would allow, reducing measurement time while maintaining accuracy.
3Measurement precision
If light source light is emitted at multiple phases, then phase difference information is enriched, but signal loss increases
Solution Approach 1:
The system performs preliminary actions by emitting light source light at multiple phases (0°, 90°, 180°, 270°) before the actual measurement is complete. This preliminary multi-phase emission ensures that sufficient phase difference information is collected early in the measurement period, allowing for accurate distance calculation while minimizing the need for repeated measurements that would increase signal loss.
Solution Approach 2:
The system uses excessive action by emitting light source light at four different phases within a single measurement period, which provides more phase difference information than the minimum required. This excessive measurement approach improves measurement precision by providing redundant data for more accurate phase difference calculation, while the structured time periods ensure efficient use of each emission event.
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 configuration enables more efficient ranging by allowing simultaneous measurement across multiple phases, reducing signal loss and noise from ambient light, and improving distance measurement accuracy.
Implementation Method 1
a light receiving element in which avalanche multiplication occurs in response to a photon incident
Data Source
AI summary
A light receiving device according to an embodiment includes: a light receiving element (1000) using an SPAD; a current source (1001) that supplies a recharge current to the SPAD; a detection section (1002) that detects a voltage based on a current, inverts an output signal in a case where a voltage value of the detected voltage exceeds a threshold value, shapes the inverted output signal into a pulse signal, and outputs the pulse signal; a plurality of counters (201(1) to 201(N)) that each counts the pulse signal output from the detection section; and a distribution section (1101) that selects a target counter to which the pulse signal is to be supplied from the plurality of counters, in which distribution section selects the target counter by a plurality of control signals corresponding to the plurality of counters on a one-to-one basis, the plurality of control signals including a state of simultaneously selecting two or more counters among the plurality of counters.