Indirect ToF Pixel Readout With Decoupling for Dark Current Reduction

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Solution Overview

Problem

Existing 3D image acquisition technologies face challenges in distinguishing signals from objects from undesired background signals and ambient light, particularly in outdoor conditions, and suffer from high dark current and power consumption in pixel array sensors, especially in non-silicon based devices.

Innovation Solution

Implementing decoupling circuits between storage nodes and floating diffusions in time-of-flight pixel circuits to allow high voltage swings for increased full well capacity while limiting overdrive, thereby managing dark current and reducing parasitic leakage currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If long exposure times are used for demodulation signaling in pixel arrays, then signal detection capability is improved, but power consumption increases

Engineering Contradiction:

Improvesignal detection capabilityVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The pixel array is divided into multiple blocks, with each block containing multiple pixels that share common readout circuitry. This segmentation allows independent control of exposure times for different pixel blocks, enabling shorter exposure times to be used while maintaining adequate signal detection capability through coordinated readout of multiple pixels within each block.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic control of exposure times for different pixel blocks based on signal strength and noise characteristics. The exposure time is adjusted in real-time during the imaging process, allowing the system to optimize between signal detection capability and power consumption by extending exposure only when necessary and using shorter exposure times when signals are strong.

Inventive Principle:

Principle #15Dynamics

2Quantity of substance

If high voltage swings are applied to storage nodes, then full well capacity is increased, but dark current and parasitic leakage currents increase

Engineering Contradiction:

Improvefull well capacityVSAvoiddark current and parasitic leakage currents

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

A feedback circuit is introduced as an intermediary between the storage node and the floating diffusion. This feedback circuit monitors the voltage at the storage node and adjusts the feedback voltage to compensate for dark current and parasitic leakage currents, allowing high voltage swings to be applied to the storage node to increase full well capacity while maintaining low dark current at the floating diffusion.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the voltage at the storage node is continuously monitored and compensated. The feedback voltage is adjusted dynamically to counteract the effects of dark current and parasitic leakage, enabling the system to maintain high full well capacity without suffering from increased dark current.

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If multiple cameras are used for stereo imaging, then 3D image capability is improved, but device size and complexity increase

Engineering Contradiction:

Improve3D image capabilityVSAvoiddevice complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical approach of using multiple physical cameras with a single camera equipped with a divided pixel array. The pixel array is segmented into multiple blocks that can be independently controlled to simulate the functionality of multiple cameras, thereby achieving 3D imaging capability while reducing device complexity and size.

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 effectively reduces dark current and power consumption, enabling efficient 3D image capture with improved signal differentiation and reduced power usage, particularly in devices with size and power constraints.

Implementation Method 1

a photodetector configured to photogenerate charge in response to incident light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS12526549B2Readout architectures for dark current reduction in indirect time-of-flight sensors

Publication Date: 2026.01.13 OMNIVISION TECHNOLOGIES INC

AI summary

A pixel circuit includes a photodiode configured to photogenerate charge in response to reflected modulated light incident upon the photodiode. A first floating diffusion is configured to store a first portion of charge photogenerated in the photodiode. A first transfer transistor is configured to transfer the first portion of charge from the photodiode to the first floating diffusion in response to a first phase signal. A first storage node is configured to store the first portion of charge from the first floating diffusion. A first decoupling circuit has a first output responsive to a first input. The first input is coupled to the first floating diffusion and the first output is coupled to first storage node. A voltage swing at the first output is greater than a voltage swing at the first input.