Dual-Frequency Pulsed ToF Measurement for Extended Range and Lower Memory Use
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Solution Overview
Problem
Existing Time-of-Flight (ToF) systems face challenges in extending the maximum unambiguous range while maintaining distance precision and reducing memory requirements, particularly in indirect ToF systems with continuous modulated signals and direct ToF systems with discrete pulses.
Innovation Solution
Emitting a first and second pulsed signal with different frequencies, storing detected signals in a memory spanning each frequency's period, and determining a virtual distance difference to calculate the actual distance, allowing for extended unambiguous range and reduced memory usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the modulation frequency is lowered to extend the maximum unambiguous range, then the maximum unambiguous range is extended, but the distance precision is lowered
Solution Approach 1:
The patent segments the distance measurement into two independent parts: a coarse distance measurement using low-frequency modulation to determine the unambiguous range, and a fine distance measurement using high-frequency modulation to determine precision. The final distance is calculated by combining these two measurements, effectively resolving the contradiction between range and precision.
Solution Approach 2:
The patent introduces a frequency dimension to the measurement system by using multiple modulation frequencies simultaneously. This allows the system to achieve both extended range (through low frequency) and high precision (through high frequency) by operating in the frequency domain rather than being constrained to a single frequency trade-off.
2Measurement precision
If the bin width is reduced to improve precision, then the distance precision is improved, but the memory size increases significantly
Solution Approach 1:
The patent segments the histogram into two parts: a coarse histogram with fewer bins for low-frequency measurements (extending range) and a fine histogram with more bins for high-frequency measurements (improving precision). By processing measurements at different frequencies separately and combining results, the system achieves high precision without requiring a single massive histogram for all distances.
Solution Approach 2:
The patent dynamically adjusts the histogram bin configuration based on the modulation frequency being used. When high-frequency modulation is applied for precision measurements, the system uses a finer bin structure; when low-frequency modulation is used for range extension, the system uses a coarser bin structure. This dynamic adaptation allows high precision with reduced memory requirements.
3Length of stationary object
If the number of histogram bins is increased to extend maximum range, then the maximum detectable range is extended, but the device complexity increases
Solution Approach 1:
The patent segments the range measurement into coarse and fine components, using low-frequency modulation for coarse range estimation (requiring fewer bins) and high-frequency modulation for fine range refinement (requiring more bins). This segmentation allows the system to achieve extended range without maintaining a single complex high-bin-count histogram for all distances.
Solution Approach 2:
The patent changes the modulation frequency parameter to control the balance between range and complexity. By switching between low and high frequencies, the system can adapt the effective histogram resolution and memory requirements, achieving extended range with manageable device complexity through parameter variation rather than fixed high complexity.
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 method extends the maximum unambiguous range, maintains precision independent of distance, and reduces memory requirements, enhancing system performance and cost-effectiveness.
Implementation Method 1
Time-of-Flight (ToF) based systems may be used to provide depth and/or distance information for two- or three-dimensional imaging or scanning
Implementation Method 2
using the detected signals to identify a portion of the first pulsed signal reflected by the target and a portion of the second pulsed signal reflected by the target
Data Source
AI summary
We disclose a method of measuring a distance to or from a target, the method comprising: operating an emitter to generate a first pulsed signal and a second pulsed signal in a field of view of the emitter in which a target may be present, the first pulsed signal having a first pulse frequency and the second pulsed signal having a second pulse frequency, the first pulse frequency being different from the second pulse frequency; operating a detector to detect signals for a pre-determined duration after said first pulsed signal is generated and for a pre-determined duration after said second pulsed signal is generated; storing said detected signals in a memory spanning a period of the first pulsed signal and a period of the second pulsed signal, respectively; using the detected signals to identify a portion of the first pulsed signal reflected by the target and a portion of the second pulsed signal reflected by the target; determining a first virtual distance based on a difference between a reference signal and the detection of the portion of the first pulsed signal reflected by the target; determining a second virtual distance based on a difference between the reference signal and the detection of the portion of the second pulsed signal reflected by the target; and determining the distance to the target based on a virtual difference corresponding to a difference between the first virtual distance and the second virtual distance.