Capacitive Position Sensor Switched Capacitor Filter
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Solution Overview
Problem
Capacitive proximity sensors in contactless smartcards face reduced sensitivity due to poor ground connection, leading to inadequate 2-dimensional sensing for online handwriting recognition, and existing solutions either degrade sensitivity or increase measurement time, limiting effective detection of handwritten characters.
Innovation Solution
A capacitive position sensor system utilizing a switched capacitor filter structure with multiple capacitors per sensing element, where each sensing element comprises two capacitors with weighted summing, allowing for noise filtering and efficient position determination in one or two dimensions, reducing the need for drive signals and increasing sample rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the integration capacitor is increased to improve sensor sensitivity, then the sensitivity is improved, but the measurement time is extended
Solution Approach 1:
The sensor array is divided into multiple independently controllable sensing elements that can be measured in parallel. Each sensing element has its own switched capacitor integrator circuit, allowing simultaneous measurement across the entire sensor array rather than sequential measurement, thus improving sensitivity without extending total measurement time.
Solution Approach 2:
The system uses periodic switching of the integrator circuits with optimized timing sequences. By carefully controlling the switching periods and phases of different sensing elements, the system achieves high measurement precision while maintaining fast sampling rates through efficient time-multiplexed operation.
2Device complexity
If only one sensor is measured at a time to simplify the measurement process, then the circuit complexity is reduced, but the total effective sensor area is reduced to the size of an individual sensor
Solution Approach 1:
Multiple sensing elements are merged into a single measurement system where their outputs are combined through the switched capacitor integrator architecture. The system measures multiple sensors simultaneously by combining their signals in the frequency domain through periodic switching, effectively utilizing the entire sensor array area while maintaining manageable circuit complexity through shared integration resources.
Solution Approach 2:
The system transitions from spatial measurement (measuring one sensor at a time) to frequency-domain measurement (measuring multiple sensors simultaneously through periodic switching). By converting the measurement problem into the frequency domain through time-periodic switching, the system achieves parallel measurement capability without proportionally increasing circuit complexity.
3Reliability
If a large integration capacitor is used to filter noise, then the noise filtering is improved, but the amount of measurements that can be executed within one second is reduced
Solution Approach 1:
The integration function is segmented across multiple smaller integrator circuits operating in parallel rather than using one large integrator. Each integrator processes signals from specific sensing elements simultaneously, providing adequate noise filtering through integrated switching sequences while maintaining high measurement throughput through parallel operation.
Solution Approach 2:
The system uses periodic switching sequences with optimized duty cycles to achieve effective noise filtering without requiring large integration capacitance. By carefully designing the switching periods and using correlated double sampling techniques, the system filters noise while maintaining fast measurement rates through efficient use of measurement windows.
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 enhances sensor sensitivity and reduces noise impact, enabling faster and more accurate position detection in contactless smartcards, supporting efficient online handwriting recognition without increasing measurement time.
Implementation Method 1
each sensing element comprising a first capacitor having a first electrode and a second electrode and a second capacitor having a first electrode and a second electrode, wherein each first electrode is coupled via a switch to a voltage supply to form a switched capacitor filter
Data Source
AI summary
A capacitive position sensor system for determining the position of an object, in particular on a surface of a contactless smartcard, is provided. The object is positioned within a sensitive area of the capacitive position sensor system and changes the capacitance of capacitors being arranged underneath the object. The capacitive position sensor system comprises a set of sensing elements being arranged in the form of a column. Each sensing element includes a first capacitor having a first electrode and a second electrode and a second capacitor having a first electrode and a second electrode. A specific weighting factor is assigned to each capacitor. A control unit is adapted to determine the position of the object in one dimension by analyzing the results of a plurality of sensed voltage levels for the first capacitors and the second capacitors of a plurality of integration cycles.