Two-Tap Image Sensor Circuit for ToF Overflow Detection

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Solution Overview

Problem

Existing image sensors using indirect Time-of-Flight (ToF) technology face increased area burden due to the need for multiple analog-to-digital converters and are prone to information errors from electronic saturation in pixel units.

Innovation Solution

An image sensor with a 2-tap pixel structure and an overflow detection circuit that detects electronic saturation through a simple structure, utilizing a current path to ground voltage when pixel signal voltages drop below a threshold, and performs logic operations on tap pixel signals to prevent errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple analog-to-digital converters are used in indirect ToF technology, then measurement precision is improved, but device complexity and area increase

Engineering Contradiction:

Improvedepth measurement precisionVSAvoidanalog-to-digital converter quantity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the overflow detection function from the complex analog-to-digital conversion process and implements it through a dedicated overflow detection circuit that monitors pixel signal voltages. This allows the system to detect saturation conditions without requiring multiple ADCs, thereby maintaining measurement precision while reducing device complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an overflow detection circuit as an intermediary component between the pixel array and the signal processing unit. This circuit monitors the voltage levels of pixel signals and detects overflow conditions, serving as a mediator that prevents information errors without requiring additional analog-to-digital converters.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If pixel signal voltage threshold is used for overflow detection, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveoverflow detection accuracyVSAvoidoverflow detection circuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the detection parameter from complex signal analysis to simple voltage level monitoring. By monitoring whether the pixel signal voltage drops below a predetermined threshold, the system achieves reliable overflow detection through a straightforward parameter change approach, avoiding complex circuit structures.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If direct ToF with small pulse width is used, then measurement precision is improved, but luminous flux decreases

Engineering Contradiction:

Improvedistance measurement precisionVSAvoidluminous flux

Core Design Contradiction:

Measurement precisionVSIllumination intensity

Solution Approach 1:

The patent employs periodic action by using modulated light in indirect ToF measurement. Instead of using short pulse widths that reduce luminous flux, the system uses periodic modulation of the light source and detects the phase difference of the reflected modulated light, achieving precise distance measurement while maintaining adequate luminous flux.

Inventive Principle:

Principle #19Periodic action

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

Prevents information errors by accurately detecting overflow in pixel units, reducing the risk of electronic saturation and improving the precision of depth measurement in image sensors.

Implementation Method 1

detecting overflow of the first tap pixel based on a first tap pixel signal outputted from the first tap pixel and overflow of the second tap pixel based on a second tap pixel signal outputted from the second tap pixel by detecting when a voltage of the first tap pixel signal or a voltage of the second tap pixel signal drops below a predetermined voltage

Methodology Applied

Scientific EffectVoltage threshold detection:

Implementation Method 2

distances may be measured by irradiating light from a light source near an image sensor and measuring the time taken for the light to be reflected off an object and returned

Methodology Applied

Scientific EffectTime of Flight: Time of Flight

Implementation Method 3

electrons are generated in a pixel circuit by a majority current that is created through an application of a substrate voltage, and the generated electrons are detected by using a potential difference between electric fields

Methodology Applied

Scientific EffectMajority current generation:

Implementation Method 4

the generated electrons are detected by using a potential difference between electric fields

Methodology Applied

Scientific EffectElectric field detection: Electric Field

Data Source

PatentUS12413872B2Image sensor and image processing system

Publication Date: 2025.09.09 SK HYNIX INC

AI summary

Disclosed is an image sensor including a first tap pixel, a second tap pixel, and an overflow detection circuit suitable for detecting overflow of the first tap pixel based on a first tap pixel signal outputted from the first tap pixel and overflow of the second tap pixel based on a second tap pixel signal outputted from the second tap pixel, and forming a current path from an overflow current source to a ground voltage terminal when a voltage of the first tap pixel signal or a voltage of the second tap pixel signal drops below a predetermined voltage.