Capacitance Sensing Circuit for Variable Signal Extraction Under Noise

Solution Overview

Problem

Conventional capacitive touch technology requires complex and costly circuits with high dynamic range and resolution analog-to-digital converters to accurately sense capacitance changes, where the significant variable signal for capacitance sensing is often overshadowed by the fixed signal, leading to increased complexity and cost without adequate parsing of the variable signal.

Innovation Solution

A capacitance sensing circuit incorporating a front-end circuit with active components, a subtracting and summing circuit, and a capacitance judging circuit, which generates and processes signals to enhance noise resistance and signal-to-noise ratio, preventing analog-to-digital converter saturation and reducing the need for large capacitors, thereby lowering the requirements on dynamic range and resolution of the analog-to-digital converter.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an analog-to-digital converter with large dynamic range and high resolution is used to parse the analog output signal, then the capacitance sensing precision is improved, but the circuit complexity and manufacture cost are increased

Engineering Contradiction:

Improvecapacitance sensing precisionVSAvoidcircuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the analog output signal into a fixed signal component and a variable signal component. The fixed signal is removed or reduced, leaving primarily the variable signal that contains the capacitance variation information. This segmentation allows the use of a lower-resolution analog-to-digital converter while maintaining sensing precision, as the converter only needs to resolve the variable portion of the signal.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the variable signal from the analog output signal by removing or suppressing the fixed signal component. This extraction process isolates the capacitance variation information, allowing it to be processed by a simpler, lower-resolution converter without losing measurement precision.

Inventive Principle:

Principle #2Taking out (Extraction)

2Measurement precision

If an analog-to-digital converter with large dynamic range and high resolution is used to parse the analog output signal, then the capacitance sensing precision is improved, but the manufacture cost is increased

Engineering Contradiction:

Improvecapacitance sensing precisionVSAvoidmanufacture cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent segments the analog output signal into a fixed signal component and a variable signal component. The fixed signal is removed or reduced, leaving primarily the variable signal that contains the capacitance variation information. This segmentation allows the use of a lower-resolution analog-to-digital converter while maintaining sensing precision, as the converter only needs to resolve the variable portion of the signal.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the variable signal from the analog output signal by removing or suppressing the fixed signal component. This extraction process isolates the capacitance variation information, allowing it to be processed by a simpler, lower-resolution converter without losing measurement precision.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If the analog output signal is parsed with high dynamic range and high resolution, then the fixed signal portion is adequately processed, but the variable signal significant to capacitance sensing is not effectively parsed

Engineering Contradiction:

Improvesignal parsing accuracyVSAvoidvariable signal parsing effectiveness

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent extracts the variable signal from the analog output signal by removing or suppressing the fixed signal component. This extraction process isolates the capacitance variation information, allowing it to be processed by a simpler, lower-resolution converter without losing measurement precision.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent applies local quality by processing only the relevant portion of the signal (the variable signal containing capacitance information) with high precision, while the fixed signal portion is handled differently (removed or reduced). This selective processing approach optimizes resource allocation and improves the effectiveness of variable signal parsing.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10466847B2Capacitance sensing circuit and touch panel for sensing capacitance changes

Publication Date: 2019.11.05 SHENZHEN GOODIX TECH CO LTD

AI summary

A capacitance sensing circuit includes: a front-end circuit, a first subtracting and summing circuit and a capacitance judging circuit; wherein the front-end circuit is coupled to the detection circuit; the first subtracting and summing circuit is coupled between the front-end circuit and the capacitance judging circuit, and includes: a subtracting unit; a summing unit, coupled to the subtracting unit; a first converter, coupled between the summing unit and the capacitance judging unit; and a second converter, coupled between the first converter and the subtracting unit; and the capacitance judging circuit is configured to judge a capacitance change of the detection capacitor. According to the present application, resistance against noise may be improved.