Capacitance-to-Voltage Conversion With Leakage Current Cancellation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional capacitance-to-voltage converters in automotive systems, such as tire pressure monitoring, face measurement errors due to substrate leakage currents caused by electrostatic discharge protection circuits, especially at high temperatures, which are exacerbated by environmental factors like dirt and humidity.
Innovation Solution
A method involving a capacitance-to-voltage converter with a reference capacitor and sampling amplifier on an integrated readout circuit that cancels out leakage currents by applying a reference voltage with alternating polarity to a series-connected sensor and reference capacitor, and charging a sampling capacitor accordingly, ensuring differential output for noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ESD protection circuits are used to protect input pins from electrostatic discharge, then ESD protection is achieved, but substrate leakage currents increase with temperature causing measurement errors
Solution Approach 1:
The patent converts the harmful leakage current into a measurable signal by applying alternating polarity reference voltages. The leakage current appears symmetrically during positive and negative half-cycles, allowing it to be distinguished from the asymmetric capacitive signal and subsequently removed through differential processing.
Solution Approach 2:
The patent changes the polarity parameter of the reference voltage alternately between positive and negative half-cycles. This parameter change causes the leakage current to manifest symmetrically while the capacitive signal manifests asymmetrically, enabling differentiation and removal of the leakage component.
2Ease of manufacture
If standard ESD protection circuits are used, then cost is reduced, but leakage currents falsify the voltage to be digitized
Solution Approach 1:
The patent converts the harmful leakage current from standard ESD protection circuits into a symmetric signal component that can be identified and removed through alternating polarity measurement and differential processing.
Solution Approach 2:
The measurement system itself generates the alternating polarity reference voltages that cause the leakage current to manifest symmetrically, enabling the system to self-diagnose and self-correct for the leakage effect without external intervention or specialized components.
3Productivity
If the sampling capacitor is connected to the sampling amplifier, then the voltage is ready for digitizing, but leakage currents cause temperature-dependent measurement errors
Solution Approach 1:
The patent applies periodic alternating polarity reference voltages to the series connection of sensor and reference capacitors. This periodic action causes leakage currents to manifest symmetrically during positive and negative half-cycles, enabling their removal through differential processing of the sampled voltages.
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
This approach effectively cancels out leakage current effects, providing precise capacitance measurements even at high temperatures and reducing the need for specialized ESD protection circuits, thus enhancing measurement accuracy and cost-effectiveness.
Implementation Method 1
a) applying a reference voltage to the series connected sensor capacitor and reference capacitor, and charging the sampling capacitor to the potential at the interconnection node between the sensor capacitor and the reference capacitor
Data Source
AI summary
A method of capacitance-to-voltage conversion with an external sensor capacitor (CP) and a capacitance-to-voltage converter (14) implemented on an integrated readout circuit that includes a reference capacitor (CR), a sampling capacitor (CS) and a sampling amplifier (22) and which has input terminals (16) to which the sensor capacitor (CP) is connected. The method comprises the steps of a) applying a reference voltage (Vref) to the series connected sensor capacitor (CP) and reference capacitor (CR) and charging the sampling capacitor (CS) to the potential at the interconnection node (A) between the sensor capacitor (CP) and the reference capacitor (CR), b) connecting the sampling capacitor (CS) to inputs of the sampling amplifier. The method further comprises the steps of c) applying the reference voltage (Vref) to the series connected sensor capacitor (CP) and reference capacitor (CR) with a polarity opposite to that in step a) and charging the sampling capacitor (CS) to the potential at the interconnection node (A) between the sensor capacitor (CP) and the reference capacitor (CR) and d) connecting the sampling capacitor (CS) to the inputs of the sampling amplifier in a polarity opposite to that in step b).