Capacitive Loading Mode Measurement Circuit with Parasitic Impedance Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive vehicle seat occupancy detection systems face systematic measurement errors due to parasitic impedances when determining the sense current of guard-sense capacitive sensors operated in loading mode, which affect the accuracy of object detection.
Innovation Solution
An impedance measurement circuit with a differential amplifier, demodulation means, and control loops to reduce the complex voltage difference between the sense and guard electrodes to zero volts amplitude and 0° phase shift, ensuring the sense current flows primarily into the sense measurement circuit, thereby minimizing systematic measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional impedance measurement circuit is used to determine sense current of a guard-sense capacitive sensor, then the measurement circuit is simple, but systematic measurement errors occur due to parasitic impedances
Solution Approach 1:
The patent implements feedback control by continuously measuring the complex voltage difference between sense and guard electrodes and adjusting the reference voltage accordingly. The control loops use the measured voltage difference to generate corrective signals that are fed back to the reference voltage source, dynamically compensating for parasitic impedance effects and maintaining measurement accuracy.
Solution Approach 2:
The patent introduces an intermediary reference voltage that is dynamically adjusted to compensate for parasitic impedances. This reference voltage acts as a mediator between the measurement circuit and the sensor, isolating the measurement from the effects of parasitic impedances and enabling accurate sense current determination.
2Adaptability or versatility
If guard electrode is kept at same electric potential as sense electrode to shape sensitivity regime, then sensitivity direction control is improved, but parasitic impedances affect measurement accuracy
Solution Approach 1:
The patent applies local quality by providing different potentials to different parts of the sensor system. The guard electrode potential is dynamically adjusted relative to the sense electrode based on local measurement conditions, allowing the sensitivity regime to be shaped while simultaneously compensating for local parasitic impedance effects through the control loops.
3Measurement precision
If periodic measurement voltage is applied to guard electrode with dynamic reference voltage, then parasitic impedance compensation is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic action by applying periodic measurement voltages to the guard electrode through the control loops. This periodic excitation enables the system to dynamically track and compensate for parasitic impedance variations, maintaining measurement precision through repeated measurement and correction cycles.
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 significantly reduces systematic measurement errors by compensating for parasitic impedances in real-time, allowing for accurate detection of object positions relative to the sense electrode.
Implementation Method 1
a differential amplifier that is configured to sense a complex voltage difference between the sense electrode and the guard electrode
Implementation Method 2
a periodic signal voltage source for providing a periodic measurement voltage to the guard electrode
Implementation Method 3
If a grounded object is approaching the sense electrode, the current flowing between the electrode and ground is increased, indicating a presence of the object
Data Source
AI summary
An impedance measurement circuit for determining a sense current of a guard-sense capacitive sensor operated in loading mode. The circuit includes a periodic signal voltage source for providing a periodic measurement voltage, a sense current measurement circuit, a differential amplifier that is configured to sense a complex voltage difference between the sense electrode and the guard electrode, a demodulator for obtaining, with reference to the periodic measurement voltage, an in-phase component and a quadrature component of the sensed complex voltage difference, and control loops for receiving the in-phase component and the quadrature component, respectively. An output signal of the first control loop and an output signal of the second control loop are usable to form a complex voltage that serves as a complex reference voltage for the sense current measurement circuit.