Sensor Electrode Heating Circuit for Parasitic-Capacitance Reduction
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Solution Overview
Problem
Existing sensor devices suffer from decreased detection sensitivity due to parasitic capacitances of high-side and low-side switches, which complicates their configuration and hinders effective capacitance detection.
Innovation Solution
A sensor device with a simplified configuration that includes a sensor electrode, an electrostatic detection circuit, a high-side switch, a low-side switch, and a controller, where the controller controls the switches to be in conductive or open states for heating and capacitance detection, respectively, and applies a predetermined voltage to minimize parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-side switch and low-side switch are used to control heating element, then heating control is achieved, but parasitic capacitances of the MOSFETs decrease detection sensitivity
Solution Approach 1:
The patent segments the control function by using a high-side switch for heating control and a separate decoupling circuit with decoupling MOSFET for capacitance detection. This segmentation allows the heating control function to be maintained while the detection function is isolated from the parasitic capacitances of the main power switches, thereby resolving the contradiction between reliable heating control and detection sensitivity.
Solution Approach 2:
The decoupling MOSFET acts as an intermediary element between the high-side switch and the heating element. During detection mode, this intermediary component is turned on to provide a low-impedance path that isolates the detection circuit from the parasitic capacitances of the high-side and low-side switches, enabling sensitive capacitance detection while maintaining the heating control functionality.
2Measurement precision
If decoupling MOSFET is added to reduce parasitic capacitance effects, then detection sensitivity is improved, but device complexity increases
Solution Approach 1:
The decoupling MOSFET is designed to serve multiple functions: it acts as a switch for capacitance detection, provides decoupling during detection mode, and can be integrated with the existing high-side and low-side switch control logic. This multi-functionality approach reduces the need for entirely separate detection circuitry, thereby improving detection sensitivity while minimizing the increase in overall device complexity.
Solution Approach 2:
The decoupling MOSFET is dynamically controlled by the gate controller to be in different states (on or off) depending on the operating mode (detection or heating). This dynamic behavior allows the circuit to optimize performance for each mode without requiring permanently active additional components, thus improving detection sensitivity while keeping the circuit relatively simple during heating operations.
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 achieves good detection sensitivity by minimizing parasitic capacitances, resulting in a sensor device with improved performance and a simpler design.
Implementation Method 1
an electrostatic detection circuit configured to detect a capacitance between the sensor electrode and an object
Implementation Method 2
the controller controls the high-side switch and the low-side switch to be in electrical conduction with each other when supplying the power for heating
Data Source
AI summary
To provide a sensor device having good detection sensitivity and simple configuration, a sensor device includes: a sensor electrode operable as a heating element; an electrostatic detection circuit for detecting capacitance of the sensor electrode; a high-side MOSFET provided between a power source for supplying power for heating and the sensor electrode; a low-side MOSFET provided between the sensor electrode and a reference potential point; a node positioned between high-side MOSFET or low-side MOSFET and the sensor electrode; and a controller for controlling high-side MOSFET and low-side MOSFET, wherein the controller controls high-side MOSFET and low-side MOSFET to be in electrical conduction with each other when supplying power for heating from the power source to the sensor electrode, and controls high-side MOSFET and low-side MOSFET to be in an open state and applies a predetermined voltage to the node when detecting the capacitance with the electrostatic detection circuit.