ToF Sensor Phase Detection Using CDS and Mask Signal
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Solution Overview
Problem
Current time-of-flight depth measurement technologies face challenges in enhancing the accuracy and reliability of distance measurements due to issues with voltage reset and capacitive coupling effects in depth sensors.
Innovation Solution
The method involves generating a periodic amplitude-modulated optical signal, detecting the phase difference between emitted and reflected signals, and using correlated double sampling (CDS) to compensate for reset voltage levels, along with a mask signal to reduce capacitive coupling effects during shuttering and resetting operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a periodic amplitude-modulated optical signal is radiated to measure distance using phase difference detection, then distance measurement capability is achieved, but reset voltage levels and capacitive coupling effects reduce measurement accuracy
Solution Approach 1:
The patent applies preliminary action by performing a reset operation on the sensing node before the actual photo-detection process. A reset control signal is generated to reset the voltage level at the sensing node during a shuttering duration, ensuring that the node starts from a known state. This preliminary reset action eliminates residual charge effects from previous measurements, thereby improving measurement accuracy and reliability.
Solution Approach 2:
The patent implements feedback through correlated double sampling (CDS). The system detects both the reset voltage level and the signal voltage level, then uses the reset level as a reference to compensate for the actual measurement. This feedback mechanism subtracts the reset voltage influence from the measured signal, effectively eliminating systematic errors and enhancing measurement precision.
2Measurement precision
If the sensing node voltage level is reset during shuttering duration, then capacitive coupling effects are reduced, but additional control signals and processing steps are required
Solution Approach 1:
The patent merges multiple functions into the mask signal. The mask signal simultaneously serves as a shutter control signal and a reset control signal, coordinating both the shuttering operation and the sensing node reset operation. This consolidation reduces the number of separate control signals needed and simplifies the overall control architecture while maintaining measurement precision.
Solution Approach 2:
The mask signal acts as an intermediary between the shutter control and reset control operations. By using the mask signal to generate both the first photo-detection control signal (for shuttering) and the reset control signal (for voltage reset), the system coordinates these operations through a single intermediary signal, reducing complexity while ensuring proper timing and synchronization.
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 improves the accuracy of distance measurements by effectively compensating for reset voltage levels and reducing capacitive coupling, leading to more reliable depth data.
Implementation Method 1
Radio-frequency (RF) modulated light sources can be used in conjunction with phase detectors. Photonic Mixer Devices (PMD) work by modulating the outgoing beam with an RF carrier, then measuring the phase shift of that carrier on the receiver side.
Implementation Method 2
A time-of-flight (ToF) depth sensor can measure the distance to an object by detecting the delay time corresponding to the phase difference between a radiated optical signal to the object and a reflected optical signal from the object.
Implementation Method 3
The illumination can use infrared light and an image sensor having a band-pass filter to make the illumination unobtrusive.
Data Source
AI summary
A method of measuring the distance to an object by radiating a periodic amplitude-modulated optical signal to the object and detecting the phase difference between the radiated optical signal and a reflected optical signal from the object includes: generating a first photo-detection control signal to control the periodic amplitude-modulation of the radiated optical signal; generating a mask signal activated at least during a shuttering duration for resetting the voltage level at a sensing node; and generating a second photo-detection control signal based on Boolean combination of the first photo-detection signal and the mask signal such that the second photo-detection signal is deactivated or masked at least during the shuttering duration.