SPAD Photon Timing With Multi-Phase TDC Histograms
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Solution Overview
Problem
SPAD-based photon detectors face challenges in achieving higher time-of-arrival (ToA) or time-of-flight (ToF) resolution due to the need for increased memory size, which results in higher costs and power consumption, and the requirement for larger on-chip histogram memories that are difficult to implement effectively.
Innovation Solution
The system divides time intervals into multiple subsets with phase-shifted many-to-one mappings of time references to memory locations, allowing for finer resolution histograms to be generated using a smaller memory by updating counts based on the phase of the avalanche timing output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the memory size is increased to achieve finer resolution or more measurement certainty, then the measurement precision is improved, but the area requirements and power consumption increase
Solution Approach 1:
The patent divides the time interval into multiple subsets (first subset and second subset) and divides the memory locations into corresponding groups. By segmenting both time and memory, the system achieves finer resolution through multi-phase sampling without requiring a proportionally larger memory structure. Each segment operates with a phase-shifted mapping, allowing the same memory to serve multiple resolution levels.
Solution Approach 2:
The patent introduces a temporal dimension by implementing phase-shifted mappings across different time subsets. Instead of increasing memory size linearly with resolution requirements, the system uses time-multiplexed phase shifts to effectively expand the measurement capability. The phase shifting adds a temporal layer to the memory addressing scheme, allowing finer resolution to be achieved through time-based differentiation rather than pure spatial expansion.
2Measurement precision
If the memory size is increased to achieve finer resolution or more measurement certainty, then the measurement precision is improved, but the power consumption increases
Solution Approach 1:
By segmenting the time intervals into multiple subsets and using phase-shifted mappings, the patent allows the same memory structure to be reused across different time phases. This segmentation enables finer measurement precision without requiring a larger, more power-hungry memory system. The memory is activated and updated in a distributed manner across time subsets rather than requiring continuous high-power operation of a larger memory array.
Solution Approach 2:
The patent employs periodic phase-shifting of the time reference mappings across different time subsets. This periodic action allows the system to cycle through different mapping phases, effectively using the same memory resources repeatedly with different phase offsets. The periodic reuse of memory locations with phase shifts achieves accumulated measurement precision without the continuous power demand that would result from a permanently larger memory structure.
3Area of stationary object
If a TDC or histogram memory with too few memory locations is used, then the area requirements and power consumption are reduced, but the resolution is too coarse and uncertainty increases
Solution Approach 1:
The patent segments the measurement process into multiple time subsets, each with its own phase-shifted mapping to memory locations. This segmentation allows a smaller memory to achieve the effective resolution of a larger memory by distributing measurements across multiple time-phased passes. Each segment contributes to the overall precision through its phase-shifted sampling of the time-of-flight data.
Solution Approach 2:
The patent adds a temporal phase dimension to the memory addressing scheme. By phase-shifting the mapping between time references and memory locations across different time subsets, the system effectively multiplies the resolution capability of the base memory structure. This dimensional approach to addressing allows finer resolution to be achieved through time-based phase differentiation rather than requiring proportionally more memory locations.
4Measurement precision
If larger on-chip histogram memories are implemented to achieve finer resolution, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent divides the histogram collection process into multiple time subsets with phase-shifted mappings, allowing a smaller, simpler memory structure to achieve the resolution of a larger memory. The segmentation approach distributes the complexity across time rather than concentrating it in a single large memory structure, making the implementation more manageable and less complex.
Solution Approach 2:
The patent uses periodic phase-shifting of time references to memory locations across different time subsets. This periodic action creates a systematic, repeating pattern that simplifies the control logic compared to managing a large complex memory structure. The regular phase-shifting cycle provides a predictable, manageable complexity pattern that is easier to implement and control than the irregular complexity of a large monolithic histogram memory.
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 approach enables the generation of histograms with higher resolution while reducing memory size and power consumption, making it feasible for cost-effective and efficient implementation in SPAD-based photon detectors.
Implementation Method 1
a SPAD configured to generate an avalanche timing output signal in response to a photon arrival
Data Source
AI summary
A method of building a moving average histogram of photon times of arrival includes, for each time interval in first and second subsets of time intervals, latching a time reference corresponding to a time of receipt of an avalanche timing output signal of a single-photon avalanche diode (SPAD), and advancing a count stored at a memory address corresponding to the latched time reference. The memory address corresponds to a range of time references. The method further includes reading and clearing a first set of counts after the first subset of time intervals; phase-shifting the sequence of time references with respect to a set of memory addresses after the first subset of time intervals; reading and clearing a second set of counts after the second subset of time intervals; and building the moving average histogram using at least the first and second sets of counts.