Capacitive Sensing Circuit Using One Oscillator for Accurate Detection

Solution Overview

Problem

Conventional capacitive sensing devices require multiple oscillators to detect capacitance variations, leading to complex circuits, increased costs, and potential detection errors due to inconsistent oscillator characteristics.

Innovation Solution

A capacitive sensing device utilizing a single oscillator, driver, switch, counter, and timer to alternately connect and disconnect a reference capacitor with a sensing capacitor, allowing for the detection of capacitance variations through oscillation signal counting and timing, eliminating the need for precise oscillator matching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple oscillators are used to detect capacitance variations, then detection capability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvecapacitance variation detectionVSAvoidcircuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges multiple oscillator functions into a single oscillator by time-division multiplexing. The single oscillator alternately connects to the reference capacitor and sensing capacitor through a switch, effectively performing the work of multiple oscillators while reducing circuit complexity and cost.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent implements periodic switching between the reference capacitor and sensing capacitor using a single oscillator. The switch alternately connects the oscillator to different capacitors in periodic intervals, enabling capacitance comparison through time-division multiplexing without requiring multiple simultaneous oscillators.

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If multiple oscillators are used to detect capacitance variations, then detection capability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvecapacitance variation detectionVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent merges multiple oscillator functions into a single oscillator by time-division multiplexing. The single oscillator alternately connects to the reference capacitor and sensing capacitor through a switch, effectively performing the work of multiple oscillators while reducing circuit complexity and cost.

Inventive Principle:

Principle #5Merging (Combining)

3Measurement precision

If multiple oscillators are used with inconsistent characteristics, then detection capability is maintained, but measurement precision deteriorates

Engineering Contradiction:

Improvedetection accuracyVSAvoidoscillator characteristic consistency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent merges multiple oscillator functions into a single oscillator by time-division multiplexing. The single oscillator alternately connects to the reference capacitor and sensing capacitor through a switch, effectively performing the work of multiple oscillators while reducing circuit complexity and cost.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces a switch as an intermediary component that mediates between the single oscillator and the two capacitors. This switch enables precise control of the oscillator's connection to different capacitors, ensuring accurate capacitance comparison without requiring multiple oscillators with consistent characteristics.

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

Simplifies the circuit design, reduces costs, and enhances detection accuracy by using a single oscillator to sense touch inputs, minimizing errors from environmental factors.

Implementation Method 1

The oscillator includes an input and an output, and the input is coupled to a reference capacitor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The counter is coupled to the output of the oscillator and configured to count value for the oscillation signal

Methodology Applied

Scientific EffectFrequency counting:

Implementation Method 3

The timer is coupled to the counter and configured to count operation periods respectively when the switch connects the reference capacitor with the sensing capacitor and when the switch disconnects the reference capacitor with the sensing capacitor

Methodology Applied

Scientific EffectTime measurement:

Data Source

PatentUS8878556B2Sensing device and method

Publication Date: 2014.11.04 NUVOTON

AI summary

A sensing device includes an oscillator, a driver, a switch, a counter and a timer. The oscillator includes an input coupled to a reference capacitor. The driver alternately sources and sinks current in accordance with an oscillation signal outputted by the oscillator. The switch connects or disconnects the reference capacitor with a sensing capacitor. The counter counts value for the oscillation signal. The timer counts operation periods respectively when the switch connects the reference capacitor with the sensing capacitor and when the switch disconnects the reference capacitor with the sensing capacitor, and the counter counts values corresponding to conditions of the switch connecting and disconnecting the reference capacitor with the sensing capacitor during the operation periods, respectively.