Capacitance Detection Circuit With Base Capacitance Offsetting

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Capacitive touch screens with flexible screens face challenges in self-capacitance detection due to high base capacitance and small capacitance variations, leading to low sensitivity and accuracy, as the small signal is easily submerged in noise and causes detection circuit saturation.

Innovation Solution

A circuit with a control module, driving module, offsetting module, and charge transfer module is used to positively or negatively charge the capacitor, offset the base capacitance, and transfer charges to generate an output voltage, improving capacitance variation detection sensitivity by eliminating the influence of base capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the detection electrode is placed closer to the system ground in flexible screens, then the base capacitance increases, but the capacitance variation becomes smaller and is submerged in noise

Engineering Contradiction:

Improvedetection stabilityVSAvoidcapacitance variation detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary anti-action by introducing an offsetting module that proactively compensates for the high base capacitance before detection. The offsetting module generates an offset signal that counteracts the base capacitance effect, allowing the detection circuit to focus on the small capacitance variation signal without being overwhelmed by the large base capacitance background.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent uses an intermediary approach by introducing a differential amplifier and offsetting module as intermediate components between the capacitor and the detection output. These intermediaries process the signal to extract the small capacitance variation from the large base capacitance, improving detection accuracy without changing the fundamental capacitor structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If a high circuit gain is used to detect small capacitance variation, then the detection sensitivity improves, but the detection circuit saturates due to high base capacitance

Engineering Contradiction:

Improvecapacitance variation detection sensitivityVSAvoidcircuit saturation issue

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the base capacitance component from the total capacitance signal using the offsetting module. By separating and compensating for the base capacitance, the detection circuit can then focus on amplifying only the small capacitance variation signal without the risk of saturation from the large base capacitance.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional approach by not directly amplifying the total capacitance signal, but rather by first compensating for the base capacitance and then amplifying the residual variation signal. This inversion of the detection sequence prevents circuit saturation while maintaining high sensitivity.

Inventive Principle:

Principle #13The other way round (Inversion)

3Length of moving object

If the sensing area is reduced using metal-mesh detection electrode, then the device thickness is reduced, but the capacitance variation becomes smaller and harder to detect

Engineering Contradiction:

Improvescreen thicknessVSAvoidcapacitance variation magnitude

Core Design Contradiction:

Length of moving objectVSMeasurement precision

Solution Approach 1:

The patent substitutes the mechanical approach of increasing sensing area with an electrical signal processing approach. Instead of making the detection electrode larger to increase capacitance variation, the patent uses electronic offsetting and differential amplification to enhance the detectability of the small capacitance variation signal from the compact metal-mesh electrode.

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

This solution enhances the sensitivity and accuracy of self-capacitance detection by reducing the impact of base capacitance, allowing for better detection of capacitance variations and improving the overall accuracy of touch control operations.

Implementation Method 1

a capacitor will be formed between a detection electrode and system ground, which is known as the self-capacitance detection

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11326907B2Circuit and method for capacitance detection, touch chip and electronic device

Publication Date: 2022.05.10 SHENZHEN GOODIX TECH CO LTD

AI summary

A circuit and method for capacitance detection, a touch chip, and an electronic device are provided. The circuit includes a control module, a driving module, an offsetting module, and a charge transfer module, the driving module being configured to positively charge a capacitor to be detected through a first charging branch circuit, or negatively charge the capacitor to be detected through a second charging branch circuit under the control of the control module; the offsetting module being configured to offset base capacitance of the capacitor to be detected through a first offsetting branch circuit under the control of the control module, or offset the base capacitance of the capacitor to be detected through a second offsetting branch circuit under the control of the control module; the charge transfer module being configured to transfer a charge on the capacitor to be detected to generate an output voltage.