SPAD Ranging Device Exposure Period Control for Frame Rate
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Solution Overview
Problem
The existing Time Of Flight (TOF) ranging method using a SPAD sensor is inefficient in generating histogram information along the depth direction, leading to a decrease in frame rate due to the sequential shifting of exposure periods.
Innovation Solution
A ranging device with a light receiving unit, exposure period control unit, information generation unit, and peak determination unit that sets exposure periods based on detected signal frequencies to quickly acquire distance information, allowing for faster data acquisition by prioritizing exposure periods corresponding to peak frequency detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If histogram information is acquired by performing measurement while sequentially shifting the exposure period, then distance information along the depth direction is obtained, but the time required to acquire distance information increases and frame rate decreases
Solution Approach 1:
The system performs preliminary measurements to identify the peak frequency position, then uses this information to prioritize subsequent measurements. By preparing and ordering exposure periods based on expected signal strength before actual measurement, the system avoids unnecessary sequential scanning and directly focuses on the most relevant depth ranges, thereby reducing acquisition time while maintaining measurement precision
Solution Approach 2:
The system dynamically changes the order and selection of exposure period parameters based on detected peak frequency. Instead of using a fixed sequential order, the exposure periods are reordered according to their expected contribution to the histogram, with periods corresponding to the peak frequency detected first. This parameter reordering optimizes the measurement sequence to achieve both precision and speed
2Loss of information
If exposure periods are sequentially shifted to generate histogram information, then complete depth range coverage is achieved, but the measurement time increases
Solution Approach 1:
The system extracts and prioritizes the most informative exposure periods based on peak frequency detection. Instead of treating all exposure periods equally in a sequential manner, it identifies and extracts the critical periods that contribute most to histogram accuracy, measuring them first while potentially reducing or skipping less informative periods, thus maintaining information completeness with reduced measurement time
Solution Approach 2:
The system performs partial measurements by focusing on a subset of exposure periods that are most relevant to the detected peak frequency. Rather than exhaustively measuring all possible exposure periods, it performs sufficient measurements on the prioritized periods to achieve the required histogram quality, accepting that some less important periods may be measured with reduced precision or skipped entirely
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 reduces the time required to acquire distance information along the depth direction, enhancing the frame rate and efficiency of the ranging process.
Implementation Method 1
a light receiving unit configured to detect an optical signal including light emitted from a light emitting unit and reflected by an object in a measurement target region and convert the optical signal into an electrical signal
Data Source
AI summary
A ranging device includes a light receiving unit of converting optical signal including light emitted from a light emitting unit and reflected by an object into pulse signal, a control unit of setting the light receiving unit to one of exposure periods corresponding classes defined according to time from emission to detection for each emission of light, an information generation unit of generating information indicating a relationship between the class and a frequency indicating the number of pulse signals, based on signal output from the light receiving unit during a frame, and a peak determination unit of determining a peak of the frequency in the information. When the peak is detected in the information acquired in a first frame, in the next second frame, the control unit sets as the exposure period in order from a period closer to a period corresponding to a class the peak is detected.