Sequencer-Driven ADC for Low-Noise Capacitive Touch Sensing

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Solution Overview

Problem

Existing microcontrollers require high processor overhead and significant program memory to perform capacitive voltage division (CVD) conversion for capacitive touch sensors, achieving only coarse timing resolution and high noise levels.

Innovation Solution

An automated sequencer is introduced to control the charging/discharging of sensor and ADC sample-and-hold capacitances, implementing the CVD conversion process as a hardware function, allowing for precise timing and reduced processor load by initiating ADC conversion with optional second or differential conversions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If software is used to perform CVD conversion, then the microcontroller can interface with capacitive touch sensors, but processor overhead increases and timing resolution becomes coarse

Engineering Contradiction:

Improvecapacitive touch sensor interfacing capabilityVSAvoidprocessor overhead

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

An automated sequencer peripheral is introduced as an intermediary hardware component between the processor and capacitive touch sensors. The sequencer executes pre-programmed CVD conversion sequences, handling the complex timing and control operations without requiring significant processor intervention. This mediator approach maintains full capacitive touch sensor functionality while dramatically reducing processor overhead and complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If software performs CVD conversion, then capacitive touch detection is enabled, but program memory consumption increases

Engineering Contradiction:

Improvecapacitive touch sensor detectionVSAvoidprogram memory usage

Core Design Contradiction:

Ease of operationVSQuantity of substance

Solution Approach 1:

The patent replaces the software-based CVD conversion mechanism with a hardware-based automated sequencer. This substitution transfers the conversion logic from program memory (software instructions) to dedicated hardware circuitry with embedded sequencing logic. The result is enabled capacitive touch sensor detection with minimal program memory consumption, as the hardware sequencer operates autonomously based on simple trigger signals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If automated sequencer is used for CVD conversion, then timing precision improves and processor overhead reduces, but device complexity increases

Engineering Contradiction:

Improvetiming resolutionVSAvoidhardware architecture

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The automated sequencer is implemented as a segmented, modular peripheral with distinct functional blocks for pre-charge control, switching sequences, and ADC triggering. This segmentation allows precise timing control for each CVD conversion phase while keeping the overall architecture manageable. The modular design achieves high timing precision without excessive device complexity by dividing the conversion process into controllable stages.

Inventive Principle:

Principle #1Segmentation

4Device complexity

If standard ADC is used without pre-charge, then conversion is simpler, but measurement precision and noise performance deteriorate

Engineering Contradiction:

Improveconversion processVSAvoidcapacitance measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The automated sequencer implements preliminary pre-charge actions before the main ADC conversion. The sequencer controls switching sequences that pre-charge the capacitive touch sensor and internal sample-and-hold capacitor to known voltage levels, ensuring accurate capacitance measurement. This preliminary preparation phase, orchestrated by the hardware sequencer, significantly improves measurement precision and noise performance while maintaining manageable conversion complexity.

Inventive Principle:

Principle #10Preliminary action

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 resolution and reduces noise in capacitive touch sensing by converting the CVD process to a hardware function, minimizing processor overhead and improving timing precision, thereby improving the detection accuracy of capacitive sensors.

Implementation Method 1

a pre-charge unit operable to independently pre-charge the external sensor capacitor and an internal sample & hold capacitor of the ADC to a selected pre-charge voltage

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

parallel switch said internal and external capacitors to share a charge

Methodology Applied

Scientific EffectCharge sharing: Capacitance

Data Source

PatentUS9071264B2Microcontroller with sequencer driven analog-to-digital converter

Publication Date: 2015.06.30 MICROCHIP TECHNOLOGY INC

AI summary

An automated sequencer for a microcontroller is provided which makes a CVD conversion process a hardware function. The sequencer controls the charging/discharging of the sensor and ADC sample-and-hold capacitances, as well as the voltage division process. It also initiates the ADC conversion, with an optional second conversion for greater resolution, or a differential conversion.