Fractional Correlation ToF Ranging Pixel Saturation

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Solution Overview

Problem

In time-of-flight (ToF) ranging, existing methods face challenges in accurately measuring phase delay due to pixel saturation and noise interference, particularly under high ambient light conditions, where the integration time is often too long, leading to invalid range measurements.

Innovation Solution

The method involves fractional correlation by reducing the correlation time to a fraction of a signal period, allowing for photon accumulation within less than half a period, thereby mitigating pixel saturation and minimizing noise influence, and using zero-force synthesis to generate orthogonal signals for accurate phase delay calculation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the correlation time is extended to improve photon accumulation and signal quality, then the measurement precision is improved, but pixel saturation occurs under high ambient light conditions

Engineering Contradiction:

Improvephase delay measurement precisionVSAvoidpixel saturation

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent implements dynamic adjustment of the correlation time parameter based on ambient light conditions. The system transitions from a fixed correlation time approach to a dynamic one where the correlation time is adapted in real-time according to the detected ambient light intensity, allowing optimal performance across varying environmental conditions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the correlation time parameter from a fixed value to a variable parameter that is adjusted based on ambient light intensity. By modifying this key parameter dynamically, the system prevents pixel saturation during bright conditions while maintaining sufficient integration time for accurate phase measurement during normal conditions

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the correlation time is reduced to prevent pixel saturation, then the harmful effects from ambient light are reduced, but the signal quality and measurement precision deteriorate

Engineering Contradiction:

Improveambient light interferenceVSAvoidphase delay measurement precision

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The system dynamically adjusts the correlation time based on real-time detection of ambient light intensity. When ambient light is high, the correlation time is reduced to prevent saturation; when ambient light is low, the correlation time is increased to improve signal quality and measurement precision

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements a feedback mechanism where the ambient light intensity is continuously monitored and used to adjust the correlation time parameter. This closed-loop control ensures that the system automatically adapts to changing environmental conditions, preventing saturation while maintaining measurement accuracy

Inventive Principle:

Principle #23Feedback

3Reliability

If the integration time is extended to improve signal accumulation, then the measurement reliability is improved, but noise interference increases under high ambient light conditions

Engineering Contradiction:

Improverange measurement reliabilityVSAvoidnoise interference

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the integration time from a fixed parameter to a dynamically adjusted parameter based on ambient light conditions. This parameter change allows the system to optimize the trade-off between signal accumulation and noise rejection in different environmental scenarios

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11709268B1Method of multi-phase correlations vector synthesis ranging by fractional correlation

Publication Date: 2023.07.25 PARK CHUN SOO

AI summary

In N-phase correlations vector synthesis time-of-flight (ToF) ranging employing N correlators, the correlation time at each signal cycle is reduced to mitigate pixel saturation by sun light or strong reflected light as well as to minimize the influence of external noise. Typically, the correlation time, during which the received signal is correlated with the transmitting signal, is set to be one full cycle in each transmitting signal period. In this invention, reducing the correlation time to1N,12⁢N, or⁢ 1k⁢Nof a full cycle period in each transmitting signal period is disclosed, where k is a real number greater than 1, but k is not 2. Depending on the intensity of the ambient light, the correlation time is flexibly and optimally selected. Multiple fractional correlations produced by a reduced correlation time are integrated over multiple signal periods to obtain more reliable signals of the correlation vectors.