SPAD Sensor Pixel-Wise Inter-Correlation Noise Filtering

Solution Overview

Problem

Current direct time-of-flight (DTOF) 3-D ranging sensors are prone to inaccurate range measurements due to noise sources like dark-count rate and background illumination, which existing methods attempt to mitigate by increasing the footprint and power consumption with redundant Single-Photon Avalanche Diodes, limiting their implementation and image resolution.

Innovation Solution

A 3-D range sensing system utilizing a pulse modulated light source and a DTOF sensor array with a pixel-wise inter-correlation photon detection system, where photon detection signals from a center pixel and adjacent pixels are processed to filter out false events based on predetermined thresholds, reducing noise effects and enhancing signal-to-noise ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If redundant Single-Photon Avalanche Diodes (SPADs) are added to filter false photon count events, then measurement precision is improved, but device area and power consumption increase significantly

Engineering Contradiction:

Improvedepth measurement accuracyVSAvoidsensor footprint

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The sensor array is divided into multiple pixels, each independently performing photon detection and inter-correlation processing. This segmentation allows noise filtering to be distributed across pixels rather than requiring a large number of redundant SPADs in each pixel, thereby reducing the footprint while maintaining measurement precision through pixel-wise inter-correlation of photon arrival times.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If redundant Single-Photon Avalanche Diodes (SPADs) are added to filter false photon count events, then measurement precision is improved, but power consumption increases

Engineering Contradiction:

Improvedepth measurement accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by stationary object

Solution Approach 1:

The sensor array is divided into multiple pixels, each independently performing photon detection and inter-correlation processing. This segmentation allows noise filtering to be distributed across pixels rather than requiring a large number of redundant SPADs in each pixel, thereby reducing power consumption while maintaining measurement precision through pixel-wise inter-correlation of photon arrival times.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces the mechanical/redundant hardware approach (adding more SPADs) with a signal processing approach (inter-correlation of photon arrival times). This substitution eliminates the need for additional physical components that would consume power, achieving noise filtering through computational methods instead of hardware redundancy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Area of stationary object

If the sensor array size is limited to reduce footprint and power consumption, then device area and power are reduced, but image resolution decreases

Engineering Contradiction:

Improvesensor footprintVSAvoidimage resolution

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical/redundant hardware approach (adding more SPADs) with a signal processing approach (inter-correlation of photon arrival times). This substitution eliminates the need for additional physical components that would consume power, achieving noise filtering through computational methods instead of hardware redundancy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary processing step (inter-correlation of photon arrival times from adjacent pixels) that enhances the information content from a limited number of pixels. This intermediary process allows the system to achieve higher effective resolution and noise immunity without increasing the physical sensor array size.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Measurement precision

If DTOF sensors operate in high-sensitivity mode to improve depth resolution, then measurement precision is improved, but susceptibility to noise increases

Engineering Contradiction:

Improvedepth resolutionVSAvoidnoise susceptibility

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary processing step (inter-correlation of photon arrival times from adjacent pixels) that enhances the information content from a limited number of pixels. This intermediary process allows the system to achieve higher effective resolution and noise immunity without increasing the physical sensor array size.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The inter-correlation process provides feedback by comparing photon arrival times across adjacent pixels and using this information to filter false events. This feedback mechanism allows the system to maintain high sensitivity for depth resolution while actively suppressing noise through the correlation of signals from multiple pixels.

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

The system effectively reduces the impact of noise, improving the signal-to-noise ratio and enabling more accurate depth measurements while maintaining a compact footprint and low power consumption, suitable for applications requiring long-range and high-resolution 3-D sensing.

Implementation Method 1

a direct time of flight (DTOF) sensor array comprising a plurality of single-photon avalanche diodes (SPADs)

Methodology Applied

Scientific EffectSingle-Photon Avalanche Diode detection: Avalanche Breakdown

Implementation Method 2

the time-of-flight (TOF) technique does not require any mechanical parts and may capture a 3-D range map close to a very high frame rate

Methodology Applied

Scientific EffectTime of flight: Time of Flight

Implementation Method 3

determining, either directly (direct TOF (DTOF)) or indirectly (indirect TOF (ITOF)), the delay between the light pulses emitted by an illuminator and a received reflected signal detected by a TOF 3-D ranging sensor

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentUS11726187B2High resolution low power inter-correlation SPAD assisted time-of-flight sensor

Publication Date: 2023.08.15 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An apparatus and method for providing a filtering false photon count events for each pixel in a DTOF sensor array are disclosed herein. In some embodiments, the apparatus includes: a light source configured to emit a modulated signal towards the object; a direct time of flight (DTOF) sensor array configured to receive a reflected signal from the object, wherein the DTOF sensor array comprises a plurality of single-photon avalanche diodes (SPADs); and processing circuitry configured to receive photon event detection signals from a center pixel and a plurality of pixels orthogonally and diagonally adjacent to the center pixel and output a valid photon detection signal, in response to determining whether a sum of the received photon event detection signals is greater than a predetermined threshold.