Capacitance Measuring Circuit Using Current Source Compensation

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Solution Overview

Problem

In capacitive touch panels and large-sized capacitive touch devices, the large parasitic capacitance requires a larger compensation capacitor, increasing the volume and cost of detection apparatuses, as existing technologies rely on compensation capacitors to cancel out basic capacitance.

Innovation Solution

A capacitance measuring circuit using a current source instead of a compensation capacitor, where the current circuit area is smaller, and the charge amount is proportional to the current input/output time, allowing for reduced current provision and smaller circuit area by controlling switching time and increasing input/output time.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a compensation capacitor is used to cancel off basic capacitance in capacitive touch panels, then the capacitance detection accuracy is improved, but the area and cost of the integrated circuit increase due to the large size of the compensation capacitor required for in-cell or large-sized touch panels

Engineering Contradiction:

Improvecapacitance detection accuracyVSAvoidintegrated circuit area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent replaces the traditional compensation capacitor (electrical component) with a current source circuit that generates compensation charge through current integration over time. This substitution eliminates the need for large-area capacitors while achieving the same capacitance compensation function, directly resolving the contradiction between detection accuracy and circuit area.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental parameter from capacitor value (fixed physical property) to current magnitude and integration time (controllable electrical parameters). By adjusting the current source strength and switching time, the compensation amount can be dynamically controlled to match the basic capacitance, achieving accurate detection without requiring large physical capacitor area.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the capacitance of the compensation capacitor is increased to match the large parasitic capacitance in in-cell touch panels, then the capacitance compensation effectiveness is improved, but the volume and cost of the detection apparatus increase

Engineering Contradiction:

Improvecapacitance compensation effectivenessVSAvoiddetection apparatus volume

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The patent substitutes the volume-dependent compensation capacitor with a current source-based compensation mechanism. The compensation charge is generated by integrating current over time (Q=I×t), replacing the volume-based charge storage (Q=C×V) approach. This eliminates the direct relationship between compensation effectiveness and physical volume.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If a large compensation capacitor is used to cancel off the large basic capacitance in large-sized capacitive touch panels, then the capacitance variation detection range is improved, but the detection apparatus cost increases

Engineering Contradiction:

Improvecapacitance variation detection rangeVSAvoiddetection apparatus cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent transforms the fixed capacitor value approach into a dynamic current integration approach. By controlling the current magnitude and integration duration, the compensation can be adapted to different touch panel sizes and capacitance ranges without changing physical component sizes, thereby maintaining detection range while reducing manufacturing cost.

Inventive Principle:

Principle #35Parameter changes

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 approach reduces the area and cost of the integrated circuit by minimizing the current required, enabling effective detection of capacitance variations without the need for large compensation capacitors.

Implementation Method 1

the charge amount provided by the current circuit will be proportional to the current input/output time

Methodology Applied

Scientific EffectCharge accumulation through current integration: Capacitance

Data Source

PatentUS10514403B2Capacitance measuring circuit and capacitance measuring method

Publication Date: 2019.12.24 RAYDIUM SEMICON

AI summary

A circuit and method of measuring capacitance are disclosed. The capacitance measuring circuit includes an integrator circuit, a first control circuit, a second control circuit and a processor circuit. The capacitance measuring method includes steps of: using a current source and a charging/discharging time to generate a first charge amount related to a second charge amount of a capacitor to be detected; generating a third charge amount and generating a fourth charge amount according to the first charge amount and the third charge amount; generating a fifth charge amount and generating a remaining charge amount according to the fifth charge amount and fourth charge amount; using an integrator to convert the remaining charge amount into a first voltage and generating a judging result according to whether the first voltage meets a second voltage; and calculating the judging result to obtain a capacitance variation of the capacitor to be detected.