ToF Photonic Mixer Charge Routing Against Cover Glass Reflections

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Solution Overview

Problem

Existing ToF imaging systems face accuracy issues due to interfering elements like cover glass reflecting infrared light, causing mixed measurements and depth ambiguities.

Innovation Solution

A ToF imaging system with a photonic mixer device using photo-sensitive elements and a control circuitry to direct charge carriers to specific elements or a drain gate, suppressing stray light and resolving depth ambiguities by controlling charge distribution through defined correlation functions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the sensor is placed underneath the cover glass to enable face authentication, then the device can perform security functions, but the infrared light is reflected by the glass causing mixed measurements and depth ambiguities

Engineering Contradiction:

Improveface authentication capabilityVSAvoiddepth measurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent divides the charge carrier collection into separate buckets (first and second charge buckets) with different integration times. The first bucket collects charge carriers during a first integration time period, and the second bucket collects charge carriers during a second integration time period. This segmentation allows the system to distinguish between reflected light from the cover glass and light from objects behind it, resolving depth ambiguities while maintaining face authentication capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs a preliminary depth measurement to determine the depth of the cover glass before conducting the actual face authentication measurement. Based on this preliminary information, the system adjusts the integration times for the first and second charge buckets to exclude the cover glass depth range from the final measurement. This preliminary action enables the system to compensate for the interfering reflections while maintaining accurate depth measurement for authentication.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If the integration time is extended to capture more light for accurate measurement, then the signal strength increases, but the depth ambiguity caused by reflections is worsened

Engineering Contradiction:

Improvesignal strengthVSAvoiddepth ambiguity

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent segments the total integration time into two distinct periods: a first integration time period for the first charge bucket and a second integration time period for the second charge bucket. By using different integration times for different buckets, the system captures sufficient light signal while being able to distinguish between reflections at different depths, thus maintaining signal strength without worsening depth ambiguity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs periodic modulation of the light source and synchronous detection with the photonic mixer device. The light source is modulated at a specific frequency, and the system performs correlated double sampling with integration times synchronized to the modulation period. This periodic action allows the system to extract accurate depth information from the modulated signal while filtering out ambient light and reflections, maintaining signal strength without introducing depth ambiguity.

Inventive Principle:

Principle #19Periodic action

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 effectively suppresses stray light reflections from cover glass, enabling accurate depth measurements by controlling charge distribution and disambiguating depth ranges, thus improving imaging accuracy.

Implementation Method 1

a photonic mixer device for performing Time-of-Flight (ToF) measurements

Methodology Applied

Scientific EffectTime-of-flight measurement: Time of Flight

Implementation Method 2

intended to detect a phase difference between an emitted light and a reflected light

Methodology Applied

Scientific EffectPhase detection:

Implementation Method 3

charge carriers generated in the photo-sensitive elements by received light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentEP4067940B1Time-of-flight imaging system and method and computer program for operating a time-of-flight imaging system

Publication Date: 2025.09.24 INFINEON TECHNOLOGIES AG

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AI summary

Examples relate to a Time-of-Flight (ToF) imaging system, and to a method and computer program for operating a ToF imaging system. The ToF imaging system comprises a photonic mixer device (20) for performing ToF measurements using at least one photo-sensitive element. Each photo-sensitive element comprises at least a first element (22) with a modifiable first charge level, a second element (24) with a modifiable second charge level, and a gate (26) for transferring charges to a fixed potential. The ToF imaging system comprises control circuitry (30) configured to provide a control signal for the photonic mixer device. The control signal is configured to drive the at least one photo-sensitive element such that charge carriers generated in the photo-sensitive elements by received light are directed either to the first element, the second element or the gate, or such that charge carriers generated in the photo-sensitive elements by received light are directed either to the first element, the second element, the gate, or to the first and the second element.