Capacitive Proximity Sensor Circuit for False Touch Discrimination

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Solution Overview

Problem

Conventional capacitive proximity-sensing technology fails to distinguish between objects held above the sensor and those in contact with device components, leading to incorrect proximity detection, such as a user touching the mobile phone casing being misinterpreted as head proximity.

Innovation Solution

A capacitive proximity sensing circuit employing guard electrodes and dual capacitive sensors, where one sensor is positioned on each side of the guard electrode to measure capacitance and produce distinct output signals, allowing differentiation between proximity above the sensor and proximity at a remote location on the device.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional capacitive proximity-sensing technology is used, then the device can detect capacitance changes, but it cannot distinguish between objects held above the sensor and objects in contact with device components

Engineering Contradiction:

Improveproximity detection accuracyVSAvoidspatial location information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The capacitive sensing system is segmented into multiple independent sensing zones with separate readout circuits. Each sensing zone (e.g., near the display, near the buttons, near the camera) operates independently and can be individually evaluated to determine the spatial location of conductive objects, thereby distinguishing between objects held above the sensor and objects in contact with device components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system transitions from a single capacitive measurement to multiple capacitive measurements across different spatial dimensions. By distributing sensors and guard electrodes throughout the device housing and comparing readings from multiple locations, the system adds spatial dimensionality to the detection, enabling differentiation of object positions beyond simple proximity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If a single capacitive sensor is used, then the circuit is simple, but it produces false positives when objects touch remote device components

Engineering Contradiction:

Improveproximity detection reliabilityVSAvoidsensor circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system uses feedback from multiple guard electrodes and sensors distributed across the device to continuously monitor capacitance changes at different locations. By comparing feedback signals from multiple zones and using logical evaluation to determine which zone experienced the capacitance change, the system achieves reliable proximity detection while filtering out false positives from remote contacts.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If optical sensors are used for proximity detection, then accurate detection can be achieved, but the cost increases and integration becomes difficult

Engineering Contradiction:

Improveproximity detection accuracyVSAvoidintegration complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The capacitive sensing system serves multiple functions: it detects proximity of conductive objects, identifies spatial location of objects, enables touch detection on various device surfaces, and provides feedback for user interface control. By making the capacitive sensing system multi-functional, the invention replaces the need for separate optical sensors while achieving comparable or superior functionality.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention replaces optical sensing mechanisms with electrical capacitive sensing. Instead of using light emission and detection (optical system), the system uses electrical field interaction with conductive objects to detect proximity and location, thereby substituting a complex optical system with a simpler electrical sensing system that can be easily integrated into the device.

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

Enables accurate distinction between user proximity above the sensor and proximity at other locations on the device, reducing false positives and improving the reliability of proximity detection.

Implementation Method 1

conventional capacitive proximity-sensing technology is unable to distinguish between an object held above the sensor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

A capacitive proximity sensing circuit employing guard electrodes and dual capacitive sensors

Methodology Applied

Scientific EffectElectrostatic shielding: Faraday Cage

Data Source

PatentUS9236861B2Capacitive proximity sensor with enabled touch detection

Publication Date: 2016.01.12 STMICROELECTRONICS INT NV

AI summary

A capacitive proximity sensor circuit capable of distinguishing between instances of detected user proximity includes one or more guard electrodes, a first sensor, and a second sensor. The capacitive proximity sensor is installed in a device such that a first sensor faces a first component of the device, and the second sensor faces a second component of the device. The first and second sensors measure a capacitance to detect proximity of a user relative to the respective sensor. The guard electrode is provided to mitigate stray capacitance to reduce error in the capacitance measurements obtained by the first and second sensors.