Sample-and-Hold Reference Circuit for Touch Sensor Noise Rejection

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Solution Overview

Problem

Existing touch and proximity detection systems face challenges in rejecting noise from voltage supplies, which affects the accuracy of measurements in human-machine interfaces, particularly when ground connections are not identical and noise sources like industrial noise and capacitive coupling are present.

Innovation Solution

A touch controller with a measurement circuit and a voltage reference circuit that uses a switched circuit with capacitors to sample and hold signals, generating a divided voltage reference that drives the shield buffer to reduce noise, allowing for effective noise rejection from the voltage supply.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a voltage reference circuit is used to provide reference voltage to measurement circuits, then measurement stability is improved, but noise from the voltage supply is coupled into the measurement channels

Engineering Contradiction:

Improvemeasurement stabilityVSAvoidsupply noise coupling

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The voltage reference circuit is segmented into multiple independent capacitors (first capacitor, second capacitor, third capacitor) that can be independently controlled and charged. This segmentation allows the circuit to selectively charge specific capacitors based on which measurement channel is active, thereby isolating noise from inactive channels while maintaining stable reference voltage for the active channel.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between different capacitor configurations based on the active measurement channel. Switches are controlled to connect different capacitors to different channels at different times, creating a dynamic reference voltage distribution system that adapts to the measurement requirements and minimizes noise coupling to each active channel.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If multiple channels are measured simultaneously in a proximity sensor, then measurement coverage is improved, but noise from voltage supply affects all channels

Engineering Contradiction:

Improvemulti-channel measurement capabilityVSAvoidnoise affecting all channels

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The reference voltage distribution is segmented into multiple independent capacitor banks, each potentially serving different measurement channels. This allows the system to provide stable reference voltage to multiple channels while isolating the noise impact to only the channel currently being measured, rather than all channels being affected simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit employs periodic switching between different capacitor configurations for different channels. By sequentially charging and discharging different capacitors in a periodic manner synchronized with the measurement cycles, the system maintains multi-channel measurement capability while ensuring that noise from the voltage supply affects only the currently active channel at any given time.

Inventive Principle:

Principle #19Periodic action

3Adaptability or versatility

If ground connections are made non-identical for different components, then system flexibility is improved, but ground loops and noise coupling increase

Engineering Contradiction:

Improveground connection flexibilityVSAvoidground loops and noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The voltage reference circuit creates equipotential conditions at critical measurement points by providing a stable, low-impedance reference voltage through capacitors. This local equipotentializing effect compensates for the non-identical ground connections elsewhere in the system, preventing ground loops and noise coupling while maintaining the flexibility of having different ground connections for different components.

Inventive Principle:

Principle #12Equipotentiality

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 achieves a significant reduction in noise, providing a 40-dB improvement in noise rejection, enhancing the accuracy of touch and proximity measurements in human-machine interfaces by isolating channels from supply noise.

Implementation Method 1

a first capacitor connected to a point between the first switch and the second switch, a second capacitor connected to the first capacitor and to the first switch

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a measurement circuit, configured to receive a signal from an active channel in a proximity sensor, and to sample and hold the signal to measure the signal

Methodology Applied

Scientific EffectSample and hold:

Data Source

PatentUS10521045B2Reference noise rejection improvement based on sample and hold circuitry

Publication Date: 2019.12.31 MICROCHIP TECHNOLOGY INC

AI summary

A touch controller may include a measurement circuit, configured to receive a signal from an active channel in a proximity sensor, and to sample and hold the signal to measure the signal. The touch controller may include a driven shield buffer. The touch controller may include a voltage reference circuit configured to generate a divided voltage reference, provide the divided voltage reference to the measurement circuit, and drive the divided voltage reference through a switched circuit to the driven shield buffer to hold channels in the proximity sensor during measurement of the active channel.