Ambient Light Sensor Dark Current Compensation via Segmented Reference Array

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Ambient light sensors face challenges in accurately measuring illumination levels due to dark current, a temperature-dependent electric current that interferes with photodiode readings, especially at low light conditions.

Innovation Solution

The implementation of an ambient light sensor design that includes a larger array of sensor elements and a smaller array of reference elements, with a light blocking element shielding the reference elements from illumination, and a current mirror system to compensate for dark current, along with a gain setting element to manage current and prevent overheating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a photodiode array is used to measure ambient light, then the sensor can detect illumination levels, but dark current interferes with measurements especially at low light conditions

Engineering Contradiction:

Improveillumination measurement accuracyVSAvoiddark current interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The photodiode array is segmented into sensor elements and reference elements. The reference elements are specifically designed to measure only dark current while sensor elements measure both light and dark current, allowing separation and subtraction of the dark current component from the total measurement.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Reference elements act as an intermediary measurement channel that captures the dark current component separately. This intermediary measurement allows the system to compensate for dark current interference by subtracting the reference element signal from the sensor element signal.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the number of sensor elements is increased to improve measurement accuracy, then sensitivity improves, but device complexity and area increase

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidsensor array complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The array is segmented into sensor elements and reference elements with different functions. This segmentation allows the system to achieve accurate dark current compensation without requiring every element to be a full sensor element, thereby reducing overall device complexity while maintaining measurement precision.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Reference elements are created as simplified copies of sensor elements that lack the light-sensitive functionality. These copied reference structures provide the necessary dark current measurement capability without the full complexity of complete sensor elements, reducing overall device complexity.

Inventive Principle:

Principle #26Copying

3Measurement precision

If reference elements are made fully shielded from light, then dark current measurement accuracy improves, but crosstalk from adjacent sensor elements increases

Engineering Contradiction:

Improvedark current measurement accuracyVSAvoidcrosstalk between elements

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The blocking element is designed with local quality variations - it provides complete light shielding for the reference element while being positioned and sized to minimize interference with adjacent sensor elements. This localized optimization allows effective dark current measurement while reducing crosstalk.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The blocking element creates an asymmetric arrangement where the reference element is fully shielded while sensor elements maintain their light-receiving capability. This asymmetric design allows the reference element to measure only dark current without receiving light, while the asymmetry in positioning and sizing minimizes crosstalk to adjacent elements.

Inventive Principle:

Principle #4Asymmetry

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 design significantly reduces crosstalk and improves sensitivity at low illumination levels by effectively canceling out dark current, enhancing the accuracy and reliability of ambient light measurements.

Implementation Method 1

each reference element comprising a blocking element to shield the reference element from being illuminated

Methodology Applied

Scientific EffectLight blocking/shielding: Absorption (EM radiation)

Implementation Method 2

each sensor element configured to provide a signal when being illuminated by light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11199442B2Ambient light detector, detector array and method

Publication Date: 2021.12.14 OSRAM OPTO SEMICON GMBH & CO OHG

AI summary

An ambient light detector, a detector array and a method are disclosed. An ambient light sensor includes a first plurality of sensor elements, where each sensor element is configured to provide a signal in response to a level of illumination and a second plurality of reference elements, each reference element configured to provide a reference signal and each including a blocking element configured to shield the respective reference element from being illuminated, where the first plurality is larger than the second plurality and the first plurality of sensor elements and the second plurality of reference elements are arranged in an array, and where a sensor element and a reference element are laterally arranged on or in a common layer substrate sharing at least one common first contact.