Capacitive Sensing Device with Transimpedance Amplifier
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Solution Overview
Problem
Capacitive sensing devices for detecting vehicle seat occupancy face challenges in maintaining sensitivity and accuracy while preventing high-frequency interference and reducing costs, particularly in designs that integrate with seat heating elements.
Innovation Solution
A capacitive sensing device featuring a transimpedance amplifier with a microcontroller and multiplexer configuration, along with protection capacitors and a low-pass filter, which maintains an alternating voltage reference and switches the antenna electrode to measure current effectively, reducing high-frequency interference and using digital signal processing to generate the alternating reference voltage, thereby enhancing sensitivity and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transimpedance amplifier with multiplexer is used to maintain alternating voltage reference, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the reference voltage generation and measurement functions into a single transimpedance amplifier circuit with an integrated multiplexer. The same amplifier maintains the alternating voltage reference on the reference voltage node while also measuring the current through the antenna electrode, eliminating the need for separate reference voltage sources and measurement circuits.
Solution Approach 2:
The transimpedance amplifier serves multiple functions simultaneously: it maintains the alternating voltage reference, measures the current through the antenna electrode, and works with the multiplexer to switch between different measurement configurations. This multi-functionality reduces the overall number of components needed in the system.
2Reliability
If protection capacitors and low-pass filters are added to filter high-frequency interference, then reliability is improved, but device complexity increases
Solution Approach 1:
The protection capacitor acts as an intermediary element that provides a low-impedance path for high-frequency interference currents, diverting them away from the sensitive measurement circuitry. The low-pass filter serves as a mediator between the antenna electrode and the transimpedance amplifier, allowing desired frequency components to pass while blocking harmful high-frequency interference.
3Ease of manufacture
If digital signal processing is used to generate alternating reference voltage, then manufacturing cost is reduced, but measurement precision may be affected
Solution Approach 1:
The patent replaces traditional analog oscillators or function generators with a digital signal processing approach implemented in a microcontroller. The microcontroller generates the alternating reference voltage through digital techniques, which simplifies the hardware requirements and reduces manufacturing costs while maintaining adequate signal quality for capacitive sensing applications.
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 provides a cost-effective capacitive sensing device that maintains sensitivity and accuracy by filtering out high-frequency interference and utilizing digital signal processing, enabling reliable detection of seat occupancy with reduced measurement offsets and improved performance.
Implementation Method 1
an antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode
Implementation Method 2
a transimpedance amplifier configured to maintain the alternating voltage equal to an alternating reference voltage on a reference voltage node by injecting a current into the antenna electrode and to measure the current
Data Source
AI summary
A capacitive sensing device includes an antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode and a control and evaluation circuit that includes a transimpedance amplifier configured to maintain the alternating voltage equal to an alternating reference voltage on a reference voltage node by injecting a current into the antenna electrode and to measure the current. The control and evaluation circuit includes a microcontroller and a multiplexer configured and arranged to switch the antenna electrode alternately to a current input of the transimpedance amplifier and to the alternating reference voltage node. The microcontroller is configured to control the multiplexer. The multiplexer and the transimpedance amplifier and a low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement. The current input node of the transimpedance amplifier is AC-coupled to the reference voltage node by a protection capacitor.