ToF Pixel Circuit 5T Architecture Background Light Interference
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Solution Overview
Problem
Current time-of-flight (ToF) systems face challenges in accurately determining depth information due to limitations in phase shift measurement and interference from background light, particularly in discontinuous illumination methods.
Innovation Solution
The proposed solution involves a pixel circuit architecture with a 5T configuration, utilizing FETs to control the operation modes of photodiodes and perform correlated double sampling, and a 4-Tap image sensor arrangement to interleave phases and reduce background light interference, enabling accurate depth calculation through interpolation of electrical charges across multiple phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If discontinuous illumination method is used for ToF measurement, then power consumption is reduced and depth measurement capability is enabled, but background light interference increases and measurement precision deteriorates
Solution Approach 1:
The patent applies periodic action by modulating the light source continuously at a specific frequency and using synchronous demodulation to detect the phase shift of the reflected light. This periodic modulation allows the system to distinguish the modulated signal from unmodulated background light, thereby maintaining measurement precision while reducing background light interference effects
Solution Approach 2:
The patent implements feedback through correlated double sampling that measures both in-phase and quadrature components of the reflected light signal. By using these feedback measurements to calculate the phase shift and depth information, the system can accurately determine depth while compensating for background light interference
2Reliability
If continuous-wave illumination with phase shift measurement is used, then depth information can be obtained through phase detection, but background light interference reduces measurement reliability
Solution Approach 1:
The patent converts the harmful effect of background light into a beneficial measurement approach by using synchronous detection. The system measures the phase shift of the modulated signal relative to the modulation frequency, which allows it to extract depth information while inherently rejecting unmodulated background light that does not carry the modulation frequency signature
Solution Approach 2:
The patent introduces an intermediary approach by using correlation detection as a mediator between the reflected light signal and the depth measurement. The correlation operation selectively amplifies the modulated signal component while suppressing background light, thereby improving measurement reliability in the presence of background interference
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 the accuracy and reliability of depth measurement by minimizing background light interference and improving phase shift measurement, allowing for more precise time-of-flight calculations and 3D image generation.
Implementation Method 1
a photodiode capable of generating electrical current according to an incoming light signal
Data Source
AI summary
A pixel circuit includes: a photodiode capable of generating electrical current according to an incoming light signal; a control circuit coupled to the photodiode for selectively coupling a cathode of the photodiode to a first reference voltage to generate the electrical current according to a first control signal; and an output circuit coupled to the control circuit for selectively coupling a second reference voltage to a connecting terminal between the control circuit and the output circuit and to generate an output signal according to a reset signal and a select signal.