iToF Range Calculation Using Dual-Frequency Phase De-Aliasing
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Solution Overview
Problem
Existing LiDAR systems face limitations in unambiguous measurable range and resolution due to distance aliasing and high computational demands in indirect time of flight measurement techniques, particularly in iToF systems, which require high modulation frequencies for accurate distance measurement.
Innovation Solution
An optical range calculation apparatus and method that employs alternating modulation frequencies to generate phase angle measurements, using a range de-aliasing unit to calculate an extended phase angle, thereby increasing the unambiguous measurable range without compromising signal-to-noise ratio, through simple computational techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high modulation frequency is used in iToF systems, then measurement precision is improved, but unambiguous measurable range is reduced
Solution Approach 1:
The patent applies periodic action by using multiple modulation frequencies in alternating periods. The system switches between a first modulation frequency (higher) and a second modulation frequency (lower) across different time periods, allowing phase angle measurements to be taken at both frequencies. This periodic alternation enables the system to achieve both high precision (when using higher frequency) and extended unambiguous range (when using lower frequency), resolving the contradiction between measurement precision and measurable range.
2Length of stationary object
If computational techniques are used to de-alias phase angles, then unambiguous measurable range is extended, but computational overhead increases
Solution Approach 1:
The patent applies parameter changes by utilizing the phase angle measurements obtained at two different modulation frequencies. The system changes the modulation frequency parameter between measurement periods and uses the difference in phase angles (which corresponds to the difference in unambiguous ranges) to calculate the true extended phase angle. This approach extends the measurable range while keeping computational requirements manageable, as it relies on straightforward phase angle comparison and calculation rather than complex de-aliasing algorithms.
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 effectively extends the unambiguous measurable range and maintains signal quality by de-aliasing phase angles, allowing for more accurate and efficient distance measurements with reduced computational overhead.
Implementation Method 1
illuminate a scene with light using the illumination source, and detect light reflected from an object in the scene
Implementation Method 2
process light reflected by features of the scene... application of a time-of-flight (ToF) calculation in order to determine the distance
Implementation Method 3
detect light reflected from an object in the scene using a detection device, for example an array of photodiodes... converted to an electrical signal
Data Source
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AI summary
An apparatus (100) comprises a light source that emits light modulated selectively at first and second modulation frequencies. A photonic mixer cell (102) generates and stores a plurality of electrical output signals respectively corresponding to phase offset values applied in accordance with an indirect time of flight technique and in respect of the selected modulation frequency. A signal processing circuit processes a first number of the electrical output signals at the first modulation frequency to calculate a first measurement phase angle (ϕ1) from a calculated first measurement vector, and a second number of the electrical output signals at the second modulation frequency to calculate a second measurement phase angle (ϕ2) from a second calculated measurement vector. A phase angle difference (Δϕ) between the first and second measurement phase angles (ϕ1, ϕ2) is then calculated and a correction value (ϕcorr) applied to the phase angle difference (Δϕ) to yield an extended range phase angle (ϕext) for calculating a range.