Touch Switch Input Noise Reduction via Analog Switch Capacitor Control

Solution Overview

Problem

Conventional touch switches face issues with input noise due to insufficient area for GND or VDD pads on PCBs, leading to button bouncing and wear, which increases noise and requires larger error tolerance in timers/counters.

Innovation Solution

A device comprising a microcontroller, noise reduction device, analog switch, and RC circuit, where the noise reduction device is connected to ground or voltage to charge or discharge the equivalent capacitor of a turned-off analog switch to zero or a specific value, reducing noise and optimizing PCB layout.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If pads for GND and VDD are disposed around the touch switch on the PCB to reduce noise, then noise is reduced, but the area occupied by the layout on the PCB increases

Engineering Contradiction:

ImprovenoiseVSAvoidPCB layout area

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The invention extracts the noise reduction function from the PCB layout (GND and VDD pads) and relocates it to the analog switch component itself by adding a noise reduction device with a capacitor connected to the switch terminal. This removes the need for extensive PCB pad areas while maintaining noise reduction effectiveness.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces a noise reduction device comprising a capacitor as an intermediary element between the analog switch and ground. This capacitor acts as a local noise sink that eliminates the need for large PCB ground pads by providing noise discharge path directly at the component level.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Area of stationary object

If the area for GND or VDD is insufficient on the PCB, then PCB layout space is saved, but considerable noise is generated

Engineering Contradiction:

ImprovePCB layout areaVSAvoidnoise

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The invention extracts the noise reduction function from the PCB layout (GND and VDD pads) and relocates it to the analog switch component itself by adding a noise reduction device with a capacitor connected to the switch terminal. This removes the need for extensive PCB pad areas while maintaining noise reduction effectiveness.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces a noise reduction device comprising a capacitor as an intermediary element between the analog switch and ground. This capacitor acts as a local noise sink that eliminates the need for large PCB ground pads by providing noise discharge path directly at the component level.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If software parameters are adjusted and larger error tolerance is set in timer/counter to accommodate input noise, then system reliability is maintained, but the timer/counter requires a larger number of bits

Engineering Contradiction:

Improvesystem reliabilityVSAvoidtimer/counter bit width

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention applies preliminary action by discharging the capacitor before each touch signal measurement to eliminate residual charges that could cause noise. This pre-clearing action ensures accurate measurement without requiring increased timer/counter precision or larger bit widths.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention replaces the software-based noise handling approach (adjusting parameters and increasing timer precision) with a hardware-based solution (capacitor discharge mechanism). This hardware intervention directly eliminates noise at the source, avoiding the need for more complex timer/counter configurations.

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 effectively reduces input noise in touch switches, saving PCB layout space and improving user interface performance by minimizing noise and error tolerance requirements.

Implementation Method 1

an equivalent capacitor 220 has already existed. The amount of charges stored in the equivalent capacitor 220 depends on where the equivalent capacitor 220 appears and on the operation time of the analog input unit 210

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a device and a method for reducing input noise using a noise reduction device turned on and connected to a ground or a voltage so that a plurality of charges stored in an equivalent capacitor of a turned off analog switch are released or accumulated to zero or a specific value

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS7671669B2Device and method for reducing input noise

Publication Date: 2010.03.02 HOLTEK SEMICON INC

AI summary

A device and a method for reducing input noise providing at least a microcontroller. The microcontroller comprises: at least a noise reduction device, at least an analog switch and at least a signal output unit. The noise reduction device connected to the ground or a voltage is turned on to charge or discharge a stray capacitor existing on a turned off analog switch so that the amount of charge stored in the stray capacitor is zero or a specific value. Thereby, the noise in a touch switch is reduced and the cost of layout on the PCB is saved.