SPAD ToF Histogram Restoration for Distance Accuracy

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Solution Overview

Problem

In ToF sensors using SPADs, there is a discrepancy between the actual photon amount incident on the diodes and the signal output, leading to reduced distance measurement accuracy.

Innovation Solution

A distance measuring device with a light projecting section, light receiving section, integration section, and restoration section that converts a first histogram into a second histogram to improve measurement accuracy by restoring the signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a ToF sensor uses SPADs to measure distance by histogram of flight time, then distance measurement can be achieved, but there is a discrepancy between actual photon amount and signal output leading to reduced measurement accuracy

Engineering Contradiction:

Improvedistance measurement accuracyVSAvoidphoton amount information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent applies feedback by using the detected signal to estimate the state of the light receiving section (such as saturation level or detection efficiency), and then using this estimated state to correct the histogram data. The restoration section feeds back the corrected histogram to improve the accuracy of distance measurement, creating a closed-loop system that compensates for the information loss.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes parameters of the histogram data based on the estimated state of the light receiving section. By adjusting histogram parameters (such as amplitude or distribution) according to the detected photon amount discrepancy, the system restores the accurate photon amount information that was lost during detection, thereby improving measurement precision.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If the light receiving section detects a large number of photons, then more signal is obtained, but the detection efficiency decreases due to saturation or dead time effects

Engineering Contradiction:

Improvephoton detection quantityVSAvoiddetection accuracy

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent performs preliminary estimation of the light receiving section's state (such as saturation level) before final distance calculation. By estimating the detection efficiency based on the detected signal characteristics, the system prepares correction factors in advance that are then applied to restore the accurate photon amount, preventing the loss of measurement precision that would otherwise occur due to saturation effects.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If the SPAD operates at high detection efficiency, then more photons are detected, but the dynamic range is reduced leading to saturation at higher light levels

Engineering Contradiction:

Improvephoton detection efficiencyVSAvoiddynamic range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent dynamically changes the interpretation parameters of the detected signal based on the estimated state of the light receiving section. By adjusting histogram parameters according to the detected photon amount and estimated efficiency, the system maintains accurate measurement across a wide dynamic range, effectively adapting to different light levels without saturation.

Inventive Principle:

Principle #35Parameter changes

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 solution enhances distance measurement accuracy by restoring the signal to a waveform closer to the original, thereby suppressing inaccuracies in distance measurement.

Implementation Method 1

a light source that emits pulsed irradiation light

Methodology Applied

Scientific EffectLight emission: Light

Implementation Method 2

measures a distance to an object using a plurality of planarly arranged single photon avalanche diodes (SPADs)

Methodology Applied

Scientific EffectPhoton detection: Photoelectric Effect

Implementation Method 3

a restoration section that converts the first histogram into a second histogram on a basis of a state of the light receiving section

Methodology Applied

Scientific EffectSignal restoration:

Data Source

PatentUS20250314752A1Distance measuring device, distance measuring method, and recording medium recording program

Publication Date: 2025.10.09 SONY GROUP CORP

AI summary

A distance measuring device according to an embodiment includes a light projecting section that emits pulsed irradiation light, a light receiving section in which a plurality of pixels each detecting incidence of a photon is arranged, an integration section that creates a first histogram for each of the pixels by using a detection signal output from each of the pixels, and a restoration section that converts the first histogram into a second histogram on the basis of a state of the light receiving section.