Capacitive Sensing with Sinusoidal Demodulation for Odd-Harmonic Noise

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Solution Overview

Problem

Capacitive sensors are prone to external noise, particularly at odd harmonics of the operation frequency, which affects their sensitivity and accuracy in detecting touch or hover events.

Innovation Solution

The integration of a mixer and a signal generator that generates a rectified sinusoidal waveform to attenuate odd harmonics, reducing sensitivity to noise and increasing the signal-to-noise ratio by operating within the linear range and preventing analog saturation, thereby enhancing noise immunity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional capacitive sensing is used, then the sensing channel can detect capacitance changes, but the sensing channel becomes sensitive to external noise at odd harmonics of the operation frequency

Engineering Contradiction:

Improvecapacitance measurement accuracyVSAvoidexternal noise sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies sinusoidal demodulation to convert the harmful effect of odd harmonic noise into a beneficial filtering mechanism. By modulating the sensing channel with a sinusoidal signal at the operation frequency and demodulating the output, the system selectively attenuates odd harmonics while preserving the fundamental frequency capacitance measurement. This transforms the noise sensitivity problem into a frequency-selective measurement advantage, where the demodulation process inherently rejects the harmful odd harmonic components that previously degraded measurement precision.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the operational parameters of the sensing channel by introducing sinusoidal modulation at a specific operation frequency. The sensing channel is configured to operate at this frequency, and the demodulation process is tuned to this same frequency. This parameter change creates a frequency domain separation where the desired capacitance signal at the fundamental frequency can be distinguished from noise at odd harmonics, thereby improving measurement accuracy while reducing noise sensitivity through frequency-selective detection.

Inventive Principle:

Principle #35Parameter changes

2Speed

If the sensing channel operates at high frequency to improve response speed, then the sensitivity to odd harmonics increases, reducing the signal-to-noise ratio

Engineering Contradiction:

Improvesensing response speedVSAvoidsignal-to-noise ratio

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent converts the harmful high-frequency noise sensitivity into a beneficial frequency-selective measurement capability. By implementing sinusoidal demodulation at the operation frequency, the system exploits the frequency domain characteristics to separate the desired signal from odd harmonic noise. The demodulation process inherently provides frequency filtering, allowing high-speed operation while maintaining a high signal-to-noise ratio by rejecting the harmful odd harmonic components that become more prominent at higher frequencies.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces sinusoidal modulation and demodulation as intermediary processes between the high-frequency sensing operation and the final measurement. The modulation stage converts the capacitance variations into frequency-domain signals, and the demodulation stage recovers the capacitance information while filtering out odd harmonic noise. This intermediary frequency-domain processing enables the system to operate at high speeds while maintaining reliability by using the modulation/demodulation pair as a mediator that separates signal from noise in the frequency domain.

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

This approach effectively reduces noise sensitivity to odd harmonics, improving the signal-to-noise ratio and enhancing the accuracy of capacitance sensing systems without major modifications to the existing sensing channel.

Implementation Method 1

a mixer that is configured to modulate a sensed input to reduce noise and increase the signal-to-noise ratio

Methodology Applied

Scientific EffectSinusoidal demodulation:

Implementation Method 2

a signal generator that generates a rectified sinusoidal waveform

Methodology Applied

Scientific EffectRectified sinusoidal waveform generation:

Data Source

PatentUS11307712B2Systems, methods, and devices for capacitive sensing with sinusoidal demodulation

Publication Date: 2022.04.19 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

Systems, methods, and devices improve the sensitivity of capacitive sensors. Devices may include an attenuator configured to receive an input from at least one sense electrode of a capacitive sensing device. The attenuator may be included in a sensing channel of a capacitive sensor. Devices may further include a signal generator coupled to an input of the attenuator. The signal generator may include one or more processors configured to generate a sinusoidal signal based, at least in part, on one or more noise characteristics of a scan sequence associated with one or more transmit electrodes of the capacitive sensing device, and provide the sinusoidal signal to the input of the attenuator.