SPAD Image Sensor Memory Segmentation for Power Reduction

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Solution Overview

Problem

Existing image sensing devices face challenges in reducing unnecessary power consumption, particularly when storing time-to-digital converter (TDC) data corresponding to single photon avalanche diode (SPAD) pulses.

Innovation Solution

The proposed image sensing device incorporates a pixel configured to generate SPAD pulses, a time-to-digital converter (TDC) to generate TDC data representing the time of flight, and a TDC memory that stores this data in a unit memory determined by the number of SPAD pulse occurrences, thereby minimizing the number of unit memories in operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If all unit memories are kept in operation to store TDC data, then data storage capacity is sufficient, but power consumption increases

Engineering Contradiction:

Improvestorage capacityVSAvoidpower consumption

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

The memory is divided into multiple unit memories (first unit memory, second unit memory, etc.), each capable of independently storing TDC data. This segmentation allows the system to activate only the necessary number of unit memories based on the count of SPAD pulses, rather than keeping all unit memories operational simultaneously, thus reducing power consumption while maintaining sufficient storage capacity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically adjusts the number of active unit memories based on the number of SPAD pulse occurrences. When the count of SPAD pulses is low, fewer unit memories are activated; when the count is high, more unit memories are activated. This dynamic adaptation optimizes the balance between storage capacity and power consumption.

Inventive Principle:

Principle #15Dynamics

2Quantity of substance

If the number of unit memories is increased to handle high SPAD pulse counts, then data storage capability improves, but device complexity increases

Engineering Contradiction:

Improvedata storage capabilityVSAvoidmemory structure complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The memory structure is segmented into multiple independent unit memories, each with a standardized architecture. This segmentation allows the system to scale storage capability by activating more unit memories rather than designing a single complex memory structure, thereby managing device complexity through modular repetition of simple units.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system activates only the necessary number of unit memories based on the actual count of SPAD pulses, rather than always maintaining all unit memories in a ready state. This partial action approach provides sufficient storage capability when needed while avoiding the complexity of maintaining a large number of always-ready memory units.

Inventive Principle:

Principle #16Partial or excessive action

3Measurement precision

If the SPAD remains active to detect all incident light, then detection accuracy is maintained, but power consumption increases

Engineering Contradiction:

Improvedetection accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The SPAD is dynamically controlled to operate only when necessary for detecting incident light within a predetermined time period. The system activates the SPAD based on the need to detect photons and turns it off when the storage capacity is full or when detection is not required, thereby maintaining detection accuracy during active periods while reducing power consumption during inactive periods.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The SPAD operates in periodic intervals rather than continuously, being activated only during periods when incident light detection is required and deactivated during periods when storage is full or detection is unnecessary. This periodic operation maintains measurement precision when needed while significantly reducing overall power consumption.

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

This approach reduces peak current consumption by minimizing the number of unit memories operating during TDC data storage and minimizes power consumption by turning off the SPAD when the storage capacity is full.

Implementation Method 1

a pixel configured to generate a pixel signal having a single photon avalanche diode (SPAD) pulse by detecting incident light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

a time-to-digital converter (TDC) configured to generate time-to-digital converter (TDC) data representing a time of flight (TOF) for the SPAD pulse

Methodology Applied

Scientific EffectTime of flight measurement: Time of Flight

Data Source

PatentUS12323723B2Image sensing device and imaging device including the same

Publication Date: 2025.06.03 SK HYNIX INC

AI summary

An image sensing device includes a pixel configured to generate a pixel signal having a single photon avalanche diode (SPAD) pulse by detecting incident light, a time-to-digital converter (TDC) configured to generate time-to-digital converter (TDC) data representing a time of flight (TOF) for the SPAD pulse, and a TDC memory configured to store the TDC data in a unit memory that is determined from among a plurality of unit memories according to the number of occurrences of the SPAD pulse.