Ambient Light Sensor Pinned Photodiode Screen Interference

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Solution Overview

Problem

Conventional ambient light sensing devices in multifunction mobile phones face integration challenges due to screen light interference, leading to precision loss and thermal noise accumulation during measurements.

Innovation Solution

Implementing a method with synchronized acquisition phases controlled by periodic disruptive light source extinction phases, using pinned photodiodes to accumulate and transfer charges without introducing thermal noise, and integrating these phases to obtain precise ambient light measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional ambient light sensing devices are integrated behind the display screen, then the device can be integrated in multifunction mobile phones, but the light measurement is impeded by the screen light which masks the ambient optical signal

Engineering Contradiction:

Improveintegration capabilityVSAvoidambient light measurement precision

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The display screen is controlled to periodically extinguish during acquisition phases, creating alternating illumination and extinction phases. This periodic action allows the photodetector to measure ambient light during extinction phases when the screen is off, while maintaining integration capability during illumination phases.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The harmful screen light is temporarily removed during acquisition phases by extinguishing the display. This extraction of the disruptive light source enables clean ambient light measurements without requiring physical separation of the sensing device from the display.

Inventive Principle:

Principle #2Taking out (Extraction)

2Ease of operation

If MOS transistor switching is used for charge transfer in acquisition phases, then the device can operate with standard transistor switching, but thermal noise (kT/C noise) is introduced and accumulated during successive integrations

Engineering Contradiction:

Improvetransistor switching operationVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The mechanical/electrical transistor switching mechanism is replaced with a passive charge transfer mechanism using pinned photodiodes. The transfer is achieved through potential barrier modulation rather than active transistor switching, eliminating the introduction of thermal noise while maintaining charge transfer functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

A pinned photodiode structure acts as an intermediary between the light-sensitive pixel and the integration node. This intermediary enables charge transfer through potential barrier modulation without requiring MOS transistor switching, thus avoiding thermal noise generation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If successive acquisition phases are integrated to improve measurement accuracy, then complete ambient light measurement is achieved, but thermal noise from MOS transistor switching is accumulated during integrations

Engineering Contradiction:

Improveambient light measurement accuracyVSAvoidthermal noise accumulation

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The noisy MOS transistor switching is replaced with passive charge transfer through pinned photodiodes for each successive acquisition phase. This substitution prevents thermal noise accumulation while allowing multiple phases to be integrated for improved measurement accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables accurate, noise-free ambient light measurements by synchronizing acquisition phases with disruptive light source extinction phases, reducing thermal noise and improving measurement precision in devices with integrated light-emitting display screens.

Implementation Method 1

an accumulation of charges photogenerated by at least one photosensitive pixel including a pinned photodiode

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

the transfer of the accumulated photogenerated charges to an integration node... a lowering of an electrostatic potential barrier enabling diffusion of the photogenerated charges to the integration node

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS11994424B2Method for measuring ambient light and corresponding integrated device

Publication Date: 2024.05.28 STMICROELECTRONICS (CROLLES 2) SAS

AI summary

In an embodiment a method for measuring ambient light includes successively synchronizing optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases, accumulating, in each acquisition phase, photo-generated charges by at least one photosensitive pixel comprising a pinned photodiode, wherein an area of the pinned photodiode is less than or equal to 1/10 of an area of the at least one photosensitive pixel, transferring, for each pixel, the accumulated photo-generated charges to a sensing node, converting, for each pixel, the transferred charges to a voltage at a voltage node and converting, for each pixel, the transferred charges to a digital number.