Time-Resolving Image Sensor for Low-Power 3D Depth Measurement
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Solution Overview
Problem
Current 3D imaging technologies, such as Time-of-Flight (TOF), stereoscopic imaging, and structured light methods, face limitations including high power consumption, reduced resolution at short distances, vulnerability to ambient light, and unsuitability for low-power portable devices like smartphones due to requirements for large pixels, high bit resolution sensors, and complex computational processes.
Innovation Solution
A low-power 3D imaging system using a time-resolving sensor with a pinned photodiode (PPD) as a time-to-charge converter, synchronized with a SPAD array to determine time-of-flight and reject ambient light, enabling 3D-depth measurements with a binary output and reduced ADC processing power, suitable for integration in portable devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TOF-based range imaging is used for 3D imaging, then distance measurement capability is improved, but power consumption increases and ambient light vulnerability worsens
Solution Approach 1:
The patent uses periodic light pulse projection instead of continuous illumination, where the light source emits short pulses at regular intervals. The sensor integrates photon detections over multiple periods, allowing distance measurement through time-of-flight calculation while reducing average power consumption compared to continuous operation modes
Solution Approach 2:
The patent converts the harmful effect of ambient light into a beneficial signal by using phase-modulated light pulses. The sensor detects the phase difference between transmitted and reflected modulated light, allowing it to distinguish structured light from ambient light and extract distance information even in bright environments
2Measurement precision
If high bit resolution sensors are used for 3D imaging, then measurement precision is improved, but device complexity and processing power requirements increase
Solution Approach 1:
The patent uses binary output (1-bit resolution) from the sensor, recording only whether photons were detected above a threshold during each integration period. This partial action approach sacrifices fine depth resolution but dramatically reduces sensor complexity and processing requirements, making the system suitable for portable devices
Solution Approach 2:
The patent replaces complex analog-to-digital conversion and high-resolution sensing mechanisms with a simple binary detection system. The sensor output is converted to binary values representing distance ranges, eliminating the need for high-bit ADCs and complex processing circuits
3Measurement precision
If large pixel size is used for TOF imaging, then photon detection capability is improved, but device area and portability worsen
Solution Approach 1:
The patent implements continuous integration of photon detection signals over multiple light pulse periods. The sensor accumulates detection events continuously, allowing smaller pixels to achieve the same effective sensitivity as larger pixels would provide in single-shot measurements, thereby reducing overall sensor area
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 system achieves efficient 3D-depth measurements with high ambient light rejection and low power consumption, suitable for portable devices like smartphones, while maintaining spatial resolution and reducing latency and motion blur.
Implementation Method 1
a time-resolving sensor with a pinned photodiode (PPD) as a time-to-charge converter
Implementation Method 2
synchronized with a SPAD array to determine time-of-flight and reject ambient light
Implementation Method 3
a first ratio of a magnitude of the first signal of the pair to a sum of the magnitude of the first signal and a magnitude of the second signal of the pair may be proportional to a time of flight of the one or more detected photons
Data Source
AI summary
An image sensor includes a time-resolving sensor and a processor. The time-resolving sensor outputs a first signal and a second signal pair in response detecting one or more photons that have been reflected from an object. A first ratio of a magnitude of the first signal to a sum of the magnitude of the first signal and a magnitude of the second signal is proportional to a time of flight of the one or more detected photons. A second ratio of the magnitude of the second signal to the sum of the magnitude of the first signal and the magnitude of the second signal is proportional to the time of flight of the one or more detected photons. The processor determines a surface reflectance of the object where the light pulse has been reflected based on the first signal and the second signal pair and may generate a grayscale image.