Capacitive Sensor Charge-Transfer Circuit for Stable Capacitance Sensing
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Solution Overview
Problem
Capacitive sensor systems face challenges in accurately measuring capacitance changes due to interference and inefficiencies in charging and discharging processes, which affect their ability to detect touch or proximity effectively.
Innovation Solution
A capacitive sensor system operates in both charging and transferring modes, utilizing a switching unit to charge the sensor to predetermined voltages and a current mirror to discharge and transfer charges to a sample capacitor, enhancing anti-interference ability and stability through the use of bandgap voltage references.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitive sensor is charged by repeatedly cycling through charging and transferring modes, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The system employs periodic charging and transferring modes to repeatedly charge the capacitive sensor and transfer charges to a sample capacitor. This periodic cycling allows multiple measurements to be accumulated, improving measurement accuracy through repeated sampling while managing the time trade-off through structured measurement cycles.
2Measurement precision
If a current mirror is used to transfer charges with high precision, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
A current mirror is introduced as an intermediary device between the capacitive sensor and the sample capacitor. The current mirror accurately replicates and transfers charges by mirroring the discharge current, ensuring high measurement accuracy while isolating the complex charge transfer mechanism from the main measurement circuit.
3Reliability
If bandgap voltage references are used to stabilize voltages, then anti-interference ability is improved, but device complexity increases
Solution Approach 1:
Bandgap voltage references are used to pre-stabilize the charging voltages before the actual measurement process begins. This beforehand cushioning against voltage variations and interference ensures that the measurement process starts with stable, predictable voltage conditions, improving reliability and anti-interference ability.
4Productivity
If the switching unit rapidly switches between charging modes, then productivity is improved, but reliability decreases due to potential interference
Solution Approach 1:
The switching unit operates in periodic cycles, alternating between charging modes and transferring modes. This structured periodic action allows rapid switching between modes while maintaining measurement stability through consistent, repeatable measurement cycles that can be averaged to reduce interference effects.
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 system effectively measures capacitance by repeatedly cycling through charging and transferring modes, improving accuracy and reducing interference, thereby enhancing the detection of touch or proximity with improved stability across temperature and process variations.
Implementation Method 1
The transferring unit includes a current mirror that discharges the capacitive sensor with a discharging current until a voltage at a first end of the capacitive sensor decreases to a first predetermined voltage and transfers a number of electric charges to a sample capacitor by mirroring the discharging current
Implementation Method 2
capacitance between the two electrodes of the capacitive sensing plate are measured by repeatedly charging the capacitive sensing plate
Implementation Method 3
In the first phase, the switching unit arranges the capacitive sensor to be charged by a first supply voltage from the first end of the capacitive sensor until a voltage difference between the first and second ends of the capacitive sensor reaches a first predetermined voltage
Data Source
AI summary
A system operable between a charging mode and a transferring mode for measuring capacitance of a capacitive sensor, includes a switching unit configured to, in a first phase of the charging mode, arrange the capacitive sensor to be charged by a first supply voltage from a first end of the capacitive sensor until a voltage difference between the first end and an opposite second end of the capacitive sensor reaches a first predetermined voltage, and in a second phase of the charging mode, disconnect the first end of the capacitive sensor from the first supply voltage and couple the second end of the capacitive sensor (10) to a second supply voltage to raise a voltage at the first end of the capacitive sensor to a second predetermined voltage.