Optical Range Calculation With Photonic Mixer Phase Correction
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Solution Overview
Problem
Conventional LiDAR systems face limitations in spatial resolution and distance measurement accuracy due to high bandwidth requirements and susceptibility to errors from harmonics and multiple reflections, particularly in indirect Time of Flight (iToF) systems.
Innovation Solution
An optical range calculation apparatus and method that utilize a photonic mixer cell and signal processing circuit to calculate phase and amplitude corrections using a priori knowledge of the light source's waveform model, employing a lookup table to correct measured phase and amplitude angles, reducing the impact of harmonics and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indirect Time of Flight (iToF) systems use high modulation frequencies to achieve low stochastic distance measurement errors, then measurement precision is improved, but the unambiguous measurement range decreases
Solution Approach 1:
The patent employs multiple periodic modulation frequencies to illuminate the scene. By using a first modulation frequency for initial measurements and a second, higher modulation frequency for refined measurements, the system achieves both extended unambiguous range and high measurement precision. The periodic nature of the modulation allows for phase-based distance calculation while managing the trade-off between frequency and range.
Solution Approach 2:
The measurement process is segmented into multiple stages using different modulation frequencies. The system first performs coarse measurements with a lower frequency to establish the unambiguous range, then performs fine measurements with a higher frequency to achieve precise distance measurement. This segmentation allows the system to overcome the fundamental limitation of single-frequency iToF systems.
2Measurement precision
If iToF systems use multiple phase-stepped samples to determine phase angle and distance, then measurement capability is improved, but the system becomes susceptible to errors from multiple reflections and propagation paths
Solution Approach 1:
The patent implements a feedback mechanism where the system analyzes the received signals for consistency across multiple phase-stepped samples. By comparing measurements taken at different phases and frequencies, the system can identify and reject measurements that show signs of multiple reflections or propagation path errors, thereby improving reliability while maintaining measurement capability.
Solution Approach 2:
By using multiple periodic modulation frequencies, the system creates distinct phase relationships for direct and reflected paths. This allows the signal processing to differentiate between primary reflections and multiple-bounce reflections, reducing the impact of erroneous measurements from complex propagation paths.
3Measurement precision
If Flash LiDAR systems sample in the time domain at very high sampling rates to calculate distance directly, then distance measurement capability is improved, but the bandwidth requirement and silicon area increase, limiting the number of channels
Solution Approach 1:
The patent replaces direct time-domain sampling with a modulation-based phase measurement approach. Instead of requiring high-speed time-domain sampling circuits, the system uses amplitude modulation of the light source and phase-sensitive detection at photodiodes. This substitution dramatically reduces the bandwidth and area requirements while maintaining distance measurement capability through phase angle calculation.
Solution Approach 2:
The system changes the measurement parameter from direct time-of-flight sampling to phase angle measurement through modulation. By measuring the phase shift of modulated light rather than directly sampling the time delay, the system achieves distance measurement with much lower bandwidth requirements and reduced silicon area, enabling higher channel counts on integrated circuits.
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
Enhances the accuracy of phase and amplitude calculations in LiDAR systems, reducing errors from harmonics and multiple reflections, thereby improving spatial resolution and distance measurement precision.
Implementation Method 1
detect light reflected from an object in the scene using a detection device, for example an array of photodiodes
Implementation Method 2
illuminate a scene with light using the illumination source, and detect light reflected from an object in the scene
Data Source
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AI summary
An optical range calculation apparatus (100) comprises a light source configured to emit light in accordance with an indirect time of flight measurement technique. A photonic mixer cell (102) is configured to generate and store a plurality of electrical output signals respectively corresponding to a plurality of predetermined phase offset values applied (112) in accordance with the indirect time of flight measurement technique. A signal processing circuit (110, 124) is configured to process the plurality of electrical output signals in accordance with the indirect time of flight measurement technique in order to calculate a measurement vector and a measured phase angle from the measurement vector. The signal processing circuit (110, 124) is configured to calculate a phase angle correction value using reference illumination data and to apply the calculated phase angle correction value in order to correct the measured phase angle, and the signal processing circuit is configured to calculate a range using the corrected measured phase angle.