Capacitive Sensor Compensation Circuit for Parasitic Capacitance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Capacitive sensor devices face challenges in resolving small changes in capacitance due to the dominance of parasitic and mutual capacitances, which limits the dynamic range and resolution of capacitance changes detected by the sensors.

Innovation Solution

A compensation circuit is implemented to minimize the effects of parasitic and mutual capacitances by supplying a calibrated compensation current that cancels out the baseline capacitance, allowing for a greater number of discrete levels to represent the dynamic range of capacitance changes, thereby improving the resolution and utilization of the capacitance sensing circuit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If capacitance sensing is used to detect changes in capacitance, then the sensor can detect proximity or contact of objects, but the resolution is impaired when capacitance changes are small relative to parasitic and mutual capacitances

Engineering Contradiction:

Improvecapacitance change resolutionVSAvoidparasitic capacitance interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and separates the parasitic capacitance component from the total measured capacitance. By measuring the baseline capacitance without an object present and subtracting it from the total capacitance measurement, the system isolates only the relevant capacitance change caused by the object, thereby eliminating the harmful effect of parasitic capacitance on measurement resolution

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the measurement parameter from absolute capacitance value to capacitance change differential. By measuring the difference between baseline capacitance (without object) and current capacitance (with object), the system transforms the measurement into a relative parameter that automatically compensates for parasitic capacitance, improving the resolution of small capacitance changes

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If parasitic and mutual capacitances are present in the sensor, then the sensor can operate with standard capacitance sensing, but the dynamic range and resolution of capacitance changes are limited

Engineering Contradiction:

Improvecapacitance sensing resolutionVSAvoidcapacitance measurement system

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs a preliminary measurement of baseline capacitance before actual sensing operations. By establishing the baseline capacitance value in advance (when no object is present) and storing it for reference, the system prepares the measurement system to compensate for parasitic capacitance during subsequent measurements, improving resolution without adding complexity to the ongoing sensing operation

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

The solution enhances the ability to detect and resolve small capacitance changes, improving the dynamic range and accuracy of capacitance sensing, allowing for more precise detection of inputs such as finger proximity on touch-sensor pads and other capacitive sensing applications.

Implementation Method 1

a transmit signal is applied to a transmit electrode to induce a current at a receive electrode capacitively coupled with the transmit electrode

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

the ability to resolve changes in capacitance may be impaired if the changes in capacitance to be detected by the sensor are small relative to the capacitance of the sensor... parasitic or mutual capacitances may be represented by a larger proportion of the discrete capacitance levels

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentUS8093914B2Compensation circuit for a TX-RX capacitive sensor

Publication Date: 2012.01.10 PARADE TECHNOLOGIES LTD

AI summary

A capacitive sensor may include a transmit electrode and a receive electrode capacitively coupled with the transmit electrode. A capacitance sensing circuit senses a capacitance between the transmit and receive electrodes by applying a signal to the transmit electrode and rectifying a current waveform induced at the receive electrode. A compensation circuit reduces the effect of a mutual and parasitic capacitances of the transmit and receive electrode pair by adding a compensation current to the rectified current.