Capacitive Sensor Electrode Circuit With N-Channel MOSFET Switching

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Solution Overview

Problem

Conventional sensor devices using P-channel MOSFETs for switches result in higher ON resistance and power consumption, which is inefficient.

Innovation Solution

A sensor device utilizing N-channel MOSFETs for high-side, low-side, and decoupling switches, with a voltage regulator to maintain a higher voltage at the node between the decoupling switch and the sensor electrode, and a control circuit to manage these switches, reducing parasitic capacitance and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If P-channel MOSFETs are used for switches in the sensor device, then the device can be manufactured with conventional designs, but the ON resistance and power consumption increase

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidpower consumption

Core Design Contradiction:

Ease of manufactureVSUse of energy by moving object

Solution Approach 1:

The patent changes the key parameter of MOSFET type from P-channel to N-channel. This parameter change fundamentally alters the electrical characteristics, reducing ON resistance and power consumption while maintaining the switching functionality required for the sensor device operation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes P-channel MOSFETs with N-channel MOSFETs in the switching circuitry. This substitution leverages the superior electrical properties of N-channel MOSFETs (lower ON resistance, lower power consumption) to replace the conventional P-channel design, achieving improved energy efficiency without compromising the switching mechanism.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If P-channel MOSFETs are used for switches, then the circuit design is conventional and simple, but the ON resistance becomes higher

Engineering Contradiction:

Improvecircuit design complexityVSAvoidON resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent changes the MOSFET type parameter from P-channel to N-channel, which directly improves the ON resistance characteristic. Although this requires adjusting the gate drive voltage (from negative to positive relative to source), the overall circuit complexity remains manageable due to the well-understood characteristics of N-channel MOSFETs.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If N-channel MOSFETs are used for all switches, then power consumption is reduced, but voltage control becomes more complex

Engineering Contradiction:

Improvepower consumptionVSAvoidvoltage control

Core Design Contradiction:

Use of energy by moving objectVSEase of operation

Solution Approach 1:

The patent changes the MOSFET type to N-channel, accepting the trade-off of requiring positive gate-to-source voltage for turn-on (as opposed to negative for P-channel). This parameter change is manageable through standard gate drive circuitry and results in significant power consumption reduction due to lower ON resistance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a voltage supply circuit that acts as an intermediary to provide the appropriate gate drive voltage for the N-channel MOSFETs. This intermediary circuit ensures proper voltage control and timing for switch operation, simplifying the overall control mechanism despite the change from P-channel to N-channel devices.

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

The sensor device achieves low power consumption and improved detection sensitivity by minimizing parasitic capacitance and power usage, while facilitating production and reducing product cost and unevenness.

Implementation Method 1

the high-side switch, the decoupling switch, and the low-side switch are N-channel MOSFETs

Methodology Applied

Scientific EffectMOSFET operation: Conduction (electrical)

Implementation Method 2

reducing parasitic capacitance and power consumption

Methodology Applied

Scientific EffectParasitic capacitance: Capacitance

Implementation Method 3

an electrostatic detection circuit configured to detect a capacitance between the sensor electrode and an object

Methodology Applied

Scientific EffectElectrostatic detection: Electrostatics

Data Source

PatentUS20250298485A1Sensor device

Publication Date: 2025.09.25 ALPS ALPINE CO LTD

AI summary

To provide a sensor device having low power consumption, sensor device includes: sensor electrode operable as heating element; electrostatic detection circuit for detecting capacitance between sensor electrode and an object; high-side switch connected to power source for supplying power for heating to sensor electrode; decoupling switch; low-side switch; voltage supply circuit for supplying voltage to a node between decoupling switch and one end of sensor electrode such that voltage of the node becomes higher than voltage of reference potential point; electronic element composed of resistor or switch provided between connection point of high-side switch and decoupling switch and reference potential point; and controller for controlling high-side switch, decoupling switch, and low-side switch, wherein the source of the high-side switch and the source of the decoupling switch are connected to the connection point and are connected to the reference potential point via the electronic element.