TOF Depth Sensing Through Transmissive Cover

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Solution Overview

Problem

Existing optical time-of-flight (TOF) sensors in handheld devices, such as smartphones, face inaccuracies in depth measurements due to contamination like smudges on the cover glass, which reflect emitted light back towards the detection pixels.

Innovation Solution

The technique involves emitting light at multiple modulation frequencies through a transmissive cover and measuring the amplitude and phase shift values of the reflected signals. By decoupling these values, the method estimates the intensity of the signal reflected by the cover glass and the target object, allowing for the neutralization of spurious reflections and improvement of depth measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a transmissive cover is used to protect the TOF sensor, then the sensor is protected from environmental damage, but reflections from the cover (especially from smudges) cause inaccurate depth measurements

Engineering Contradiction:

Improvesensor protectionVSAvoiddepth measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent segments the reflected light signal into multiple frequency components using Fourier transform analysis. By measuring at multiple modulation frequencies and analyzing the spectral content, the system can separate the cover reflection component from the target reflection component, thereby resolving the measurement accuracy issue while maintaining sensor protection

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the modulation frequency parameter of the emitted light to differentiate between cover reflections and target reflections. By varying the frequency and analyzing the phase and amplitude responses at different frequencies, the system can identify and neutralize the cover reflection component, thus improving depth measurement accuracy while keeping the protective cover in place

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If multiple modulation frequencies are used to decouple reflections, then depth measurement accuracy is improved, but the complexity of the measurement system increases

Engineering Contradiction:

Improvedepth measurement accuracyVSAvoidmeasurement system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses periodic modulation of the light source at multiple known frequencies. This periodic action creates distinct spectral signatures for different reflection paths, allowing the system to separate cover reflections from target reflections through frequency domain analysis. The periodic nature of the modulation simplifies the mathematical analysis compared to using aperiodic or random frequency variations

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements a feedback mechanism where the measured phase and amplitude responses at multiple frequencies are used to calculate and subtract the cover reflection component from the total signal. This feedback loop continuously refines the depth measurement by compensating for the cover interference, achieving high accuracy without requiring complex hardware modifications

Inventive Principle:

Principle #23Feedback

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 significantly enhances the accuracy of depth measurements by effectively decoupling the reflections from the cover glass and the target, reducing errors caused by contamination and improving the overall performance of TOF sensors in handheld devices.

Implementation Method 1

emitting light from a module at a first modulation frequency and emitting light at a second modulation frequency

Methodology Applied

Scientific EffectLight: Light

Implementation Method 2

the light is emitted through a transmissive cover toward a target... an optical signal reflected by the target and an optical signal reflected by the transmissive cover

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

measuring first amplitude and phase shift values representing a combination of an optical signal reflected by the target and an optical signal reflected by the transmissive cover

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 4

TOF systems are based on a phase-measurement technique of emitted intensity-modulated light... Based on the phase information, the distance (or depth) to a point in the scene for each pixel in the sensor can be determined

Methodology Applied

Scientific EffectTime of flight: Time of Flight

Data Source

PatentUS12313779B2Depth sensing using optical time-of-flight techniques through a transmissive cover

Publication Date: 2025.05.27 AMS OSRAM ASIA PACIFIC PTE LTD

AI summary

Techniques for determining dynamically the intensity of the reflection from a transmissive cover and neutralizing it so as to improve the accuracy of depth measurements. Depth measurements of light modulation at multiple frequencies—which also can be used for depth disambiguation—are obtained and used to decouple the information to estimate the intensity of the signal reflected by the transmissive cover itself or a smudge on the transmissive cover, and the intensity of the signal reflected by the target object.