Time-of-Flight Sensor Gating for Ambient Light Noise Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Ambient light noise deteriorates the signal-to-noise ratio in time-of-flight (ToF) measurements, limiting the accuracy of depth maps, and increasing illumination power is constrained by eye safety regulations.
Innovation Solution
A time-of-flight apparatus with a light source that emits short-duration light pulses, a photo-detection portion with elements like SPADs or CMOS sensors, and a measurement circuitry that drives and drains electrons during specific time intervals to enhance signal detection while managing saturation and ambient light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If illumination power is increased to improve signal detection, then signal-to-noise ratio improves, but eye safety regulations are exceeded
Solution Approach 1:
The patent applies periodic pulsed illumination instead of continuous light emission. The light source emits light in short pulses with controlled duration and frequency, allowing the system to accumulate sufficient signal over multiple pulses while keeping instantaneous power within eye safety limits. This periodic action enables improved signal-to-noise ratio through temporal integration without exceeding safety thresholds.
Solution Approach 2:
The patent implements preliminary gating of the photo-detection element before the actual measurement. A reset phase is performed beforehand to clear any residual charge or noise from the detector, ensuring that the subsequent measurement captures only the relevant reflected light signal. This preliminary action prepares the detection system to maximize signal capture while maintaining safety constraints.
2Measurement precision
If photo-detection element is continuously active to capture all light, then ambient light is detected, but noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent employs periodic gating of the photo-detection element that is synchronized with the pulsed illumination. The detector is activated only during the expected arrival time of reflected light pulses and remains inactive during other periods. This temporal gating allows the system to capture the reflected signal while rejecting ambient light that occurs outside the gated intervals, thereby improving signal-to-noise ratio.
Solution Approach 2:
The patent extracts and isolates the relevant signal from the total light input by using time-gated detection. Only the portion of light that arrives within the specific time window corresponding to the expected flight time of the pulsed illumination is detected and processed. Ambient light occurring outside this window is effectively excluded, separating the useful signal from harmful noise.
3Measurement precision
If photo-detection time interval is extended to capture more signal, then signal-to-noise ratio improves, but saturation occurs and measurement accuracy decreases
Solution Approach 1:
The patent uses multiple short pulsed illuminations with corresponding periodic detection intervals rather than a single extended measurement period. Each pulse generates a separate detection window, allowing the system to accumulate signal from multiple pulses while resetting the detector between pulses to prevent saturation. This periodic approach maintains measurement accuracy by clearing residual charge while improving signal-to-noise ratio through temporal integration.
Solution Approach 2:
The patent performs a reset operation before each measurement interval to clear any residual charge from the photo-detection element. This preliminary action prevents carryover effects from previous measurements that could cause saturation, ensuring that each measurement starts with a clean state. The reset phase is carefully timed to allow complete charge clearance while minimizing the total measurement cycle time.
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
Improves the signal-to-noise ratio without exceeding eye safety limits by reducing pulse duration and employing gated electron drainage, enhancing the accuracy of depth measurements.
Implementation Method 1
a photo-detection portion for detecting at least the light pulse reflected from the scene within a first photo-detection time interval, wherein the photo-detection portion includes at least one photo-detection element
Data Source
AI summary
A time-of-flight apparatus has a light source for emitting a light pulse to a scene; a photo-detection portion for detecting at least the light pulse reflected from the scene within a first photo-detection time interval, wherein the photo-detection portion includes at least one photo-detection element; and a measurement circuitry configured to: drive, within a measurement time interval including the first photo-detection time interval, the at least one photo-detection element for detecting the light pulse reflected from the scene, and drain, within the measurement time interval and after the first photo-detection time interval, electrons from the at least one photo-detection element.