Sensing Circuit Parasitic Capacitance Reduction via Electrode Segmentation

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Solution Overview

Problem

The accuracy of fingerprint identification in electronic devices is compromised by parasitic capacitors between sensing wires, which affect the sensing accuracy and resolution.

Innovation Solution

The method involves dividing sensing electrodes into two groups and applying different sensing signals to each group at non-overlapping time periods, ensuring that the voltage levels of reference signals are equal to minimize the influence of parasitic capacitance on sensing accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If sensing signals are provided to multiple sensing electrodes simultaneously, then sensing coverage is improved, but parasitic capacitance between sensing wires increases and degrades sensing accuracy

Engineering Contradiction:

Improvesensing coverageVSAvoidsensing accuracy

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The sensing electrodes are divided into two groups (first group and second group), with each group connected to separate sensing wires. This segmentation allows the system to maintain comprehensive sensing coverage while reducing parasitic capacitance effects by processing groups sequentially rather than simultaneously, thus resolving the contradiction between coverage and accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sensing circuit operates in alternating time periods: during a first time period, sensing signals are provided to the first group of sensing electrodes; during a second time period, sensing signals are provided to the second group. This periodic action enables full sensing coverage while eliminating simultaneous signal interference and parasitic capacitance effects on accuracy.

Inventive Principle:

Principle #19Periodic action

2Productivity

If multiple sensing electrodes are activated at the same time, then fingerprint recognition speed is improved, but parasitic capacitance interference increases

Engineering Contradiction:

Improvefingerprint recognition speedVSAvoidparasitic capacitance interference

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The system uses periodic action by alternating between two time periods: the first time period for sensing with the first group of electrodes, and the second time period for sensing with the second group. This approach maintains high productivity through rapid alternation while eliminating parasitic capacitance interference that would occur with simultaneous activation.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The sensing operation continues without interruption by seamlessly alternating between the two groups of sensing electrodes. The first group is sensed during the first time period, then the second group is sensed during the second time period, maintaining continuous useful action for fingerprint recognition while avoiding parasitic capacitance issues.

Inventive Principle:

Principle #20Continuity of useful action

3Measurement precision

If sensing resolution is increased, then fingerprint identification accuracy is improved, but the effect of parasitic capacitors becomes more significant

Engineering Contradiction:

Improvefingerprint identification accuracyVSAvoidparasitic capacitor effect

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

By segmenting the sensing electrodes into two separate groups with dedicated sensing wires, the system can achieve high sensing resolution for accurate fingerprint identification while minimizing parasitic capacitor effects. Each group can be optimized for high resolution without the interference that would result from simultaneous operation of all electrodes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The periodic alternation between sensing the first group and the second group allows each group to be measured with high precision without the presence of other active sensing signals. This eliminates parasitic capacitance coupling between simultaneously active sensing wires, enabling high-resolution fingerprint identification.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS11900718B2Method of operating a sensing circuit to reduce effect of parasitic capacitors between sensing wires of the sensing circuit

Publication Date: 2024.02.13 INNOLUX CORP

AI summary

A sensing circuit has a plurality of sensing units and a plurality of sensing electrodes. The sensing electrodes are divided into a first group and a second group. The sensing electrodes of the first group are electrically connected to a portion of the sensing units, and the sensing electrodes of the second group are electrically connected to another portion of the sensing units. A first sensing signal is provided to the sensing electrodes of the first group in a first time period, and a second sensing signal is provided to the sensing electrodes of the second group in a second time period. The first time period and the second time period start at different times and are not overlapped with each other.