Capacitive Sensor Signal Processing Circuit Self-Capacitance Correction

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Solution Overview

Problem

Capacitive position detection sensors face issues with detection sensitivity due to the effect of self-capacitances of receiving conductors, which affect the accuracy of position detection, especially in mobile devices like smartphones where power consumption and integration complexity are concerns.

Innovation Solution

A signal processing circuit that includes a capacitor circuit, a gate circuit, and a voltage supply control circuit to detect changes in capacitance as voltage signals, allowing for the generation of a signal indicative of self-capacitance, thereby correcting for the effects of self-capacitances and improving detection sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an IV conversion section using an op-amp is used to convert weak current to voltage, then the current signal can be processed at appropriate signal levels, but power consumption increases and circuit integration becomes difficult

Engineering Contradiction:

Improvesignal levelVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent extracts the problematic IV conversion section (op-amp, capacitor, resistor) from the circuit and replaces it with a direct voltage sampling approach. The gate circuit connects the receiving conductor directly to the capacitor circuit, eliminating the need for current-to-voltage conversion while maintaining signal processing capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the electronic IV conversion mechanism (op-amp based) with a direct capacitive coupling mechanism. Instead of converting current to voltage through active components, the system directly samples the voltage change on the receiving conductor through the gate circuit and capacitor, substituting an active electronic conversion process with a passive capacitive coupling process.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If multiple receiving electrodes share a single IV conversion section, then circuit complexity is reduced, but detection timing accuracy deteriorates when pointers move quickly

Engineering Contradiction:

Improvecircuit complexityVSAvoiddetection timing

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The patent divides the signal processing function by providing a separate capacitor circuit for each receiving conductor. Instead of sharing a single IV conversion section, each receiving conductor (R1, R2, R3, R4) has its own dedicated capacitor circuit (C1, C2, C3, C4) that can be independently controlled by the gate circuit, enabling simultaneous or rapid sequential sampling without timing conflicts.

Inventive Principle:

Principle #1Segmentation

3Use of energy by moving object

If the capacitor circuit directly samples voltage from the receiving conductor, then power consumption and circuit size are reduced, but self-capacitance effects degrade detection sensitivity

Engineering Contradiction:

Improvepower consumptionVSAvoiddetection sensitivity

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent introduces the gate circuit as an intermediary between the receiving conductor and the capacitor circuit. The gate circuit controls the timing and connection of the sampling process, allowing the capacitor to charge/discharge through the gate in response to pointer proximity. This intermediary structure enables precise control of the sampling process while maintaining the low-power, direct-voltage-sampling approach.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution enhances detection sensitivity by correcting for self-capacitance effects, enabling timely and accurate position detection in capacitive position detection sensors, particularly suitable for mobile devices with reduced power consumption and smaller circuit scale.

Implementation Method 1

detects as a change in voltage signal taking place in the capacitor circuit the change in capacitance taking place between the conductor and a pointer

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

receives a signal from the active capacitive pen with a sensor electrode (conductor) through electric field coupling

Methodology Applied

Scientific EffectElectric field coupling: Electric Field

Data Source

PatentUS9678597B2Signal processing circuit, signal processing method, position detector, and electronic device for position detection sensor including sensor self-capacitance correction

Publication Date: 2017.06.13 WACOM CO LTD

AI summary

A signal processing circuit is connected to one of a plurality of conductors of a position detection sensor having a self-capacitance and configured to generate a signal indicative of the self-capacitance for use in correcting a pointer position detection signal. The circuit includes a capacitor circuit and detects a change in capacitance between the conductor and a pointer (e.g., a finger) as a change in voltage in the capacitor circuit. The signal processing circuit further includes: a gate circuit which controls the connection between the capacitor circuit and the conductor; and a voltage supply control circuit which temporarily sets, to a defined voltage level, a first end of the gate circuit to which the conductor is connected and sets a defined potential difference between the first end and another (second) end of the gate circuit to which the capacitor circuit is connected.