SPAD Array Activation for LiDAR Memory and Power Optimization
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Solution Overview
Problem
Existing Time of Flight (ToF) based ranging systems face challenges with high data volume and memory usage, and struggle with multi-target detection due to reliance on scatter points' positions for distance calculation.
Innovation Solution
A lidar system that selectively activates single photon avalanche diodes (SPADs) based on their proximity to the laser source, using a time-to-digital converter to generate histogram data, which reduces data volume and enables precise distance calculation without requiring scatter points' position determination, thereby improving memory efficiency and multi-target detection capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all SPADs are activated continuously for histogram data collection, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic activation of SPADs based on distance ranges. The logic circuit selectively activates specific SPADs corresponding to expected target distance ranges, rather than keeping all SPADs continuously active. This dynamic switching reduces power consumption while maintaining measurement precision for the relevant distance ranges.
Solution Approach 2:
The patent applies partial action by activating only a subset of SPADs necessary for the current measurement range. Instead of using the full SPAD array for all measurements, the system activates only those SPADs that correspond to the expected target distance, reducing overall power consumption while maintaining sufficient measurement precision.
2Productivity
If histogram data is collected from all SPADs simultaneously, then productivity is improved, but memory usage increases
Solution Approach 1:
The patent segments the SPAD array into multiple groups based on distance ranges, with each group associated with specific histogram data. Instead of collecting data from all SPADs into a single large histogram, the system creates separate histograms for different SPAD groups, reducing the memory required for each individual histogram while maintaining overall data collection efficiency.
Solution Approach 2:
The patent implements partial data collection by activating only specific SPADs for each measurement cycle based on the expected target range. This reduces the volume of histogram data that needs to be stored in memory, thereby reducing memory usage while maintaining productivity for the relevant measurement ranges.
3Measurement precision
If scatter points' positions are used for distance calculation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the distance calculation function directly from the SPAD activation pattern. Instead of using scatter points' positions and performing complex coordinate transformations, the system directly maps the activated SPAD indices to distance values based on pre-calibrated relationships, simplifying the device while maintaining measurement precision.
Solution Approach 2:
The patent introduces a lookup table or pre-calibrated mapping as an intermediary between SPAD activation and distance calculation. This intermediary stores the relationship between SPAD positions and corresponding distances, allowing direct distance retrieval without complex real-time calculations, thereby reducing device complexity while maintaining precision.
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 system achieves reduced power consumption, enhanced object recognition, and accurate depth measurement, particularly beneficial for applications like autonomous vehicles and 3D mapping, with improved memory efficiency and multi-target detection capabilities.
Implementation Method 1
The pixel circuit, positioned behind the optical module, generates electrical outputs based on the reflected laser signal. It comprises an array of single photon avalanche diodes (SPADs)
Implementation Method 2
The propagation time of the probing light, from emission to reception, is used to calculate the spatial distance between the object and the sensor
Data Source
AI summary
The present invention is direct to lidar systems and methods. According to an embodiment, the present invention provides a lidar system that comprises a laser source, an optical module, a pixel circuit with an array of single photon avalanche diodes (SPADs), a logic circuit, a time-to-digital converter (TDC). The laser source emits a pulsed laser, and the optical module receives the reflected laser signal. The pixel circuit, positioned behind the optical module, generates electrical outputs based on the reflected laser signal. The logic circuit activates and deactivates SPADs at different times, depending on their distances from the laser source. The TDC creates histogram data from the SPAD array, with each histogram data comprising multiple intensity values for different time bins. There are other embodiments as well.