Capacitive Tire Pressure Sensor Circuit Parasitic Capacitance
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Solution Overview
Problem
Existing electronic circuits for differential-capacitive sensors, such as tire pressure sensors, face challenges with high parasitic capacitance, high power consumption, and signal output dependency on specific circuit parameters like resistors, capacitors, clock frequency, or voltage, which affect the accuracy and efficiency of capacitance measurement.
Innovation Solution
A tire pressure monitoring system utilizing a switched capacitor circuit with non-overlapping clock phases, MEMS capacitors, a capacitance-to-voltage converter, and a sigma-delta converter, along with a common mode correction amplifier, to minimize parasitic capacitance, reduce power consumption, and generate a signal output independent of specific circuit parameters, achieving high signal-to-noise ratio and low power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electronic circuits are used to measure capacitance changes, then the measurement function is provided, but parasitic capacitances inundate the sensor capacitors causing signal attenuation and measurement precision degradation
Solution Approach 1:
The patent measures the parasitic capacitance values and uses them as calibration parameters in the measurement algorithm. By characterizing the parasitic capacitances and incorporating them into the measurement model, the harmful effect is converted into a correctable parameter, enabling accurate measurement despite the presence of parasitic capacitances
Solution Approach 2:
The patent transforms the capacitance measurement problem into a voltage measurement problem through capacitance-to-voltage conversion. By changing the measurement parameter from capacitance to voltage and using differential measurement techniques, the system achieves immunity to parasitic capacitance effects while maintaining high measurement precision
2Measurement precision
If high resolution capacitance measurement is implemented, then measurement precision is improved, but circuit power consumption increases
Solution Approach 1:
The patent implements periodic measurement cycles where the sensor is activated only when needed, with sleep modes between measurements. The system uses event-triggered measurement initiation and periodic calibration sequences, allowing high-precision measurement capability while minimizing average power consumption through duty cycling
Solution Approach 2:
The patent employs self-calibration techniques where the system automatically characterizes its own parasitic capacitances and measurement parameters without external intervention. This eliminates the need for frequent external calibration sessions that would consume additional power, allowing the system to maintain high measurement precision through autonomous self-adjustment
3Reliability
If signal output depends on specific circuit parameters, then circuit design is simplified, but measurement reliability decreases due to parameter sensitivity
Solution Approach 1:
The patent implements feedback mechanisms where measurement parameters are continuously monitored and adjusted. The system measures actual circuit parameters such as clock frequency and voltage levels and uses this information to compensate for variations in the measurement algorithm, ensuring reliable output despite parameter changes
Solution Approach 2:
The patent designs a measurement system that can operate with varying circuit parameters through software-based compensation. By implementing a universal measurement algorithm that adapts to different clock frequencies, voltage levels, and circuit configurations, the system achieves parameter independence while maintaining reliability across diverse operating conditions
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 effectively minimizes parasitic capacitance effects, achieves low power consumption, and provides a signal output independent of specific circuit parameters, resulting in a high signal-to-noise ratio and efficient capacitance measurement, suitable for integrated tire pressure monitoring systems.
Implementation Method 1
A capacitive pressure sensor, or capacitive accelerometer, conveys the state of the pressure measurement by varying the magnitude of its capacitance
Implementation Method 2
The system uses a capacitance-to-voltage converter connected to the MEMS sense capacitor
Implementation Method 3
a sigma-delta converter having a comparator with a first digital output state and a second digital output state
Implementation Method 4
tire pressure sensor MEMS capacitors, where the MEMS capacitors have at least one pair of sense capacitors that are measured differentially
Data Source
AI summary
A tire pressure monitoring system is provided that includes a switched capacitor circuit having a clock with two non-overlapping clock phases that control a state of analog switches of the switched capacitor circuit. The system uses tire pressure sensor MEMS capacitors that are measured differentially. A capacitance-to-voltage converter is connected to the MEMS sense capacitor, and a sigma-delta converter having a comparator with a first digital output state and a second digital output state is used. The first output state is a sum of reference voltages and the second output state is a difference of the reference voltages. An average value of the capacitance-to-voltage converter output is driven to a zero value and a digital output is provided of the average output states that is equal to a difference between the MEMS capacitors divided by their sum multiplied by a ratio of the reference voltages.