Capacitive Image Sensor Noise Reduction via Calibration

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Capacitive fingerprint sensors face challenges in accuracy due to manufacturing uncertainties, leading to fixed pattern noise in captured images, which increases system cost and complexity, particularly in portable devices where space is limited.

Innovation Solution

A capacitive image sensor with an array of sensing units, sample-and-hold circuits, and signal conditioning circuits that utilize positive and negative waveforms to reduce noise by amplifying and digitizing output electric potentials, effectively canceling out fixed pattern noise and improving image quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If capacitive fingerprint sensors are manufactured with high-density semiconductor processes, then the sensor can be made compact for portable devices, but manufacturing uncertainties cause fixed pattern noise that degrades image quality

Engineering Contradiction:

Improvesensor sizeVSAvoidsensing element precision

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by performing calibration measurements before actual fingerprint sensing. The system pre-characterizes each sensing element's response to known stimuli and stores this calibration data for subsequent noise compensation during operation, thereby addressing manufacturing variations before they affect image quality

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of sensing element characterization by introducing calibration factors that adjust for manufacturing variations. By measuring and storing individual sensing element parameters during calibration and using these to compensate during operation, the system maintains image quality despite high-density manufacturing uncertainties

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If calibration data is stored to eliminate fixed pattern noise, then image quality improves, but memory storage space increases system cost

Engineering Contradiction:

Improvefingerprint image qualityVSAvoidmemory storage space

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent applies partial action by storing only essential calibration parameters rather than complete calibration datasets. The system stores compact calibration factors for each sensing element that capture the essential characteristics needed for noise compensation, reducing memory requirements while maintaining image quality

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent uses copying by creating simplified representations of calibration data in the form of lookup tables and compact parameter sets. These copied representations allow the system to store essential calibration information in reduced form, decreasing memory requirements while preserving the ability to compensate for fixed pattern noise

Inventive Principle:

Principle #26Copying

3Reliability

If optical fingerprint sensing is used, then reliability is high, but the form factor cannot be kept small due to embedded optical lens size

Engineering Contradiction:

Improveidentification reliabilityVSAvoidsensor form factor

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent replaces the optical mechanical system with an electrical field-based capacitive sensing system. By substituting optical components (lenses, light sources) with electrical sensing elements that detect capacitance changes from finger contact, the system achieves compact form factor while maintaining identification reliability through electronic rather than optical measurement

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

The solution enhances the accuracy of fingerprint images by reducing noise, thereby improving personal identification capabilities while minimizing storage requirements and system costs, making it suitable for compact portable applications.

Implementation Method 1

capacitive image sensor with an array of capacitive sensing units, each capacitive sensing unit for transforming a distance between a portion of a surface of an approaching finger and a top surface thereof into an output electric potential

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10162995B2Capacitive image sensor with noise reduction feature and method operating the same

Publication Date: 2018.12.25 SUNASIC TECH INC

AI summary

A capacitive image sensor with noise reduction feature and a method operating the capacitive image sensor are provided. The capacitive image sensor includes: a number of capacitive sensing units forming an array, each capacitive sensing unit for transforming a distance between a portion of a surface of an approaching finger and a top surface thereof into an output electric potential, wherein a value of the output electric potential is changed by a driving signal coupled on the finger; at least one sample-and-hold circuit for capturing and retaining different output electric potentials; at least one signal conditioning circuit, each comprising: at least one differential amplifier for amplifying a difference between two electric potentials retained by the sample-and-hold circuit; and a driving source, for providing the driving signal to the finger.