Capacitance Detection Circuit Noise Cancellation for Touch Accuracy

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Solution Overview

Problem

Capacitive sensors in electronic devices face interference from screen noise, which affects touch detection accuracy and can saturate amplification circuits, reducing detection performance.

Innovation Solution

A capacitance detection circuit with an amplification circuit, a cancellation circuit, and a control circuit is used to convert capacitance signals into voltage signals and generate cancellation signals to counteract screen noise, ensuring accurate touch detection by isolating noise signals from useful signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If capacitance detection is performed using conventional circuits, then touch detection function is achieved, but screen noise causes detection accuracy degradation and amplification circuit saturation

Engineering Contradiction:

Improvecapacitance detection accuracyVSAvoidscreen noise influence

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies noise cancellation technology to convert the harmful screen noise into a beneficial signal processing mechanism. By detecting the noise signal through a dedicated noise detection electrode and generating a corresponding cancellation signal, the system transforms the harmful noise interference into a correctable error signal that can be subtracted from the detection result, thereby improving capacitance detection accuracy

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces a noise detection electrode as an intermediary element that specifically detects screen noise without being affected by touch signals. This intermediary component acts as a mediator between the screen noise source and the capacitance detection circuit, allowing the noise to be separately identified and cancelled before affecting the main detection accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If amplification circuit gain is increased to improve detection sensitivity, then weak touch signals are amplified, but screen noise causes circuit saturation

Engineering Contradiction:

Improvetouch signal detection sensitivityVSAvoidamplification circuit stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent segments the detection system into two independent paths: a main detection path for touch signals and a noise detection path for screen noise. By separating these functions into different electrodes and processing channels, the system can independently process and cancel noise before it reaches the amplification stage, allowing high gain operation without saturation

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs noise detection and cancellation in advance before the noise signal reaches the amplification circuit. By detecting the noise signal through the noise detection electrode and generating a cancellation signal beforehand, the system prevents noise-induced saturation at the amplifier, enabling higher gain settings for improved touch sensitivity

Inventive Principle:

Principle #10Preliminary 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

The proposed solution effectively reduces the influence of screen noise on capacitance detection, enhancing the accuracy and performance of touch control systems in electronic devices by canceling noise signals and maintaining effective detection signals.

Implementation Method 1

the controlled current source is configured to generate the second current signal according to a mirror image of the first current signal

Methodology Applied

Scientific EffectCurrent mirror:

Implementation Method 2

the cancellation circuit includes an inverter or a buffer, the control signal is a first voltage signal, the cancellation signal is a second voltage signal, and the inverter and the buffer are configured to generate the second voltage signal according to the first voltage signal

Methodology Applied

Scientific EffectInversion:

Implementation Method 3

Capacitive sensors are widely used in electronic products to implement touch detection. When a conductor, such as a finger, approaches or touches a detection electrode, a capacitance corresponding to the detection electrode changes.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11275468B2Capacitance detection circuit, touch control chip and electronic device

Publication Date: 2022.03.15 SHENZHEN GOODIX TECH CO LTD

AI summary

This application provides a capacitance detection circuit, which is configured to detect a capacitance between a sensing electrode in a screen and a first driving electrode to which a driving signal is input. The capacitance detection circuit includes: an amplification circuit, connected to the sensing electrode and configured to convert a capacitance signal between the sensing electrode and the first driving electrode into a voltage signal; a cancellation circuit, connected to the amplification circuit and configured to output a cancellation signal to the amplification circuit, where the cancellation signal is used to cancel a noise signal from the screen included in the voltage signal; and a control circuit, connected to a second driving electrode, in the screen, to which no driving signal is input, and configured to generate a control signal, where the control signal is configured to control the cancellation circuit to generate the cancellation signal.