Time-of-flight sensing with pulsed illumination and gated detection

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Solution Overview

Problem

Indirect time-of-flight (TOF) sensing systems face issues such as aliasing, depth ambiguity, ambient light saturation, and ambient light shot noise due to the harmonic nature of emitted light and the inability to effectively manage ambient light noise in pixel-level charge collection.

Innovation Solution

The implementation of an illumination module that emits light with periodic narrow pulses or a single high peak power pulse at a low duty cycle, combined with sensor modulation characteristics, allows for effective cross-correlation analysis to determine time-of-flight information, reducing aliasing and ambient light interference by selectively suppressing sensor modulation beyond a distance of interest.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If continuous modulation illumination is used for TOF sensing, then depth measurement capability is achieved, but ambient light saturation and shot noise occur

Engineering Contradiction:

Improvedepth measurement capabilityVSAvoidambient light saturation and shot noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The illumination module emits light in periodic pulse trains rather than continuous modulation. Each pulse train consists of multiple pulses at a specific repetition frequency. This periodic pulsed illumination allows the sensor to gate integration only during expected signal arrival windows, rejecting ambient light that arrives continuously, thereby reducing saturation and shot noise while maintaining depth measurement capability

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system pre-calculates and pre-sets the integration window timing based on the pulse repetition frequency and expected depth range. The sensor module is configured to integrate signals only during specific time windows that correspond to when reflected pulses are expected to arrive, before ambient light accumulation becomes problematic. This preliminary timing configuration prevents ambient light saturation before it occurs

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If high modulation frequency is used, then depth resolution is improved, but aliasing and depth ambiguity increase

Engineering Contradiction:

Improvedepth resolutionVSAvoidaliasing and depth ambiguity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The system uses periodic pulse trains with controlled repetition frequencies rather than continuous high-frequency modulation. By adjusting the pulse repetition frequency and integrating over multiple pulse periods, the system achieves effective depth resolution improvement without the aliasing problems of continuous high-frequency modulation. The periodic structure allows unambiguous depth determination within each period while extending the effective measurement range

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs continuous integration of the modulated signal over multiple pulse repetition periods. This continuous integration accumulates signal energy from multiple pulses, improving signal-to-noise ratio and depth resolution. The integration continues as long as the phase relationship between transmitted and received pulses remains consistent, providing continuous useful measurement action without the discontinuities that cause aliasing

Inventive Principle:

Principle #20Continuity of useful 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

This approach enhances the accuracy of depth measurement by minimizing aliasing and ambient light noise, improving the overall performance of TOF sensing systems by maintaining cross-correlation characteristics while being more practical to implement with readily available illumination modules.

Implementation Method 1

The emitted light reflects off of the one or more objects and is received by pixels in the sensor module

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

The emitted light reflects off of the one or more objects and is received by pixels in the sensor module to generate corresponding electrical charge

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 3

Based on the received light (e.g., the generated electrical charge), the sensor module can perform time-of-flight sensing calculations or operations to determine depth and other scene information

Methodology Applied

Scientific EffectTime of flight: Time of Flight

Data Source

PatentUS12123952B2Imaging system with time-of-flight sensing

Publication Date: 2024.10.22 SEMICON COMPONENTS IND LLC

AI summary

A time-of-flight (TOF) sensing system may include an illumination module and a sensor module. The illumination module may emit light having a reduced illumination duty cycle such as a high peak power and low width illumination pulse. The emitted light may reflect off of one or more objects as reflected light. The sensor module may include pixels operable based on a sensor modulation signal to generated image charge portions in response to the reflected light. The sensor modulation signal may be selectively suppressed after a period of time corresponding to a distance of interest. Processing circuitry in the TOF sensing system may obtain TOF information based on a phase difference between the emitted light and the image charge portions determined by cross-correlation data. By using the illumination pulse and the selective sensor modulation suppression, TOF sensing may exhibit reduced aliasing issues and improved ambient light rejection.