Two-Frequency Time-of-Flight 3D Image Sensor
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Solution Overview
Problem
Indirect time-of-flight 3D image sensors face limitations in measurement accuracy and flexibility due to pre-defined phase steps, leading to systematic errors and increased costs, and are unable to achieve high-speed depth measurement.
Innovation Solution
A 3D image system with a modulator generating two modulation signals with a predetermined frequency difference, allowing for flexible phase differences and multiple image acquisitions at different times to calculate object depth, reducing the need for complex phase shifters and calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pre-defined constant phase steps are used for depth measurement, then depth calculation can be performed with fixed acquisition sequences, but measurement accuracy deteriorates due to systematic wiggling errors and the system lacks flexibility
Solution Approach 1:
The patent applies dynamics by making the phase difference variable rather than fixed. The control unit dynamically adjusts the phase difference between illumination and sensor modulation signals based on desired measurement parameters, allowing the system to adapt to different measurement requirements while maintaining accuracy through optimized phase selection for each specific measurement scenario.
2Measurement precision
If four frame readouts with extensive calculations are used for depth estimation, then depth measurement can be performed, but measurement speed deteriorates and high speed 3D depth measurement becomes impossible
Solution Approach 1:
The patent extracts and eliminates the need for extensive post-acquisition calculations by performing phase modulation measurements in a optimized sequence that reduces computational burden. The system extracts only the necessary measurement data through intelligent acquisition timing and phase stepping, removing the requirement for processing four complete frame readouts while maintaining depth measurement capability.
3Measurement precision
If complex phase shifters are used to maintain highly precise unchanging phase steps, then phase precision can be maintained, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent replaces complex mechanical/electronic phase shifter hardware with a software-controlled timing approach. Instead of using physical phase shifters to maintain precise phase steps, the system uses the control unit to precisely time the modulation signals, substituting hardware complexity with programmable timing control that achieves the same phase precision without requiring complex phase shifter circuits.
4Measurement precision
If electronic calibration box is used to calculate wiggling error, then systematic errors can be corrected, but manufacturing time and expense increase
Solution Approach 1:
The patent implements self-service by enabling the 3DI sensor system to perform its own calibration and wiggling error correction without requiring external electronic calibration equipment. The control unit executes calibration routines using the sensor's own resources, allowing the system to correct systematic errors autonomously during manufacturing or operation, thereby eliminating the need for separate calibration boxes and reducing both time and expense.
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 enhances measurement accuracy and speed while reducing costs and complexity, enabling more flexible and precise depth measurement without the need for extensive calibration.
Implementation Method 1
at least one pixel of the pixel array is configured to receive the modulated light signal reflected from an object as a reflected modulated light signal and to demodulate the reflected modulated light signal using the second modulation signal
Implementation Method 2
Indirect time-of-flight (ToF) three-dimensional image (3DI) image sensors are based on continuously modulated light for scene illumination
Data Source
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Figure 3A~3B
Figure 4
AI summary
A three-dimensional image system includes a modulator configured to generate a first and a second modulation signal having a predetermined frequency difference, an illumination source configured to generate a light signal modulated by the first modulation signal, and a pixel array modulated by the second modulation signal. At least one pixel of the pixel array is configured to receive a reflected modulated light signal and generate a plurality of measurement signals based on a plurality of image acquisitions taken at different acquisition times. A controller is configured to control a phase difference between the first modulation signal and the second modulation signal by setting the first modulation frequency and the second modulation frequency to have a predetermined frequency difference greater than zero; and calculate a depth of the object based on the plurality of measurement signals, the depth being a distance from the 3DI system to the object.