Capacitive Touch Interface Circuit for Low-Power Smart Cards
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Solution Overview
Problem
Existing smart cards lack a user interface for entering credentials securely, leading to increased risk of credential interception due to reliance on external devices, and existing touch-based interfaces face challenges with high power consumption and limited sensitivity.
Innovation Solution
A smart card with a touch-based user interface that includes a first capacitor, a second capacitor, and an analog-to-digital converter, where a third capacitor is used to maintain voltage within an optimal conversion range, enabling efficient and accurate touch position capturing, reducing power consumption and supporting multi-channel touch sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a touch-based user interface is implemented on a smart card, then credential entry security is improved, but power consumption increases
Solution Approach 1:
The patent implements a multi-phase sampling strategy that dynamically changes the operational parameters of the capacitive sensor. During idle periods, sampling is reduced or suspended to minimize power consumption. When touch events are detected or anticipated, the sampling rate increases to capture accurate touch position data. This parameter adjustment resolves the contradiction by adapting power usage to actual operational needs rather than maintaining constant high-power operation.
Solution Approach 2:
The system employs periodic sampling of the capacitive sensor at strategically timed intervals rather than continuous monitoring. The sampling occurs at phases optimized for detecting touch events while allowing power-saving modes during intervals between expected interactions. This periodic approach maintains security functionality while significantly reducing average power consumption compared to continuous operation.
2Reliability
If a touch-based user interface is implemented on a smart card, then secure credential entry is enabled, but device complexity increases
Solution Approach 1:
The smart card's existing capacitive sensor, originally designed for basic position detection, is repurposed to serve multiple functions including touch event detection, position measurement, and credential entry validation. By making the sensor multi-functional rather than adding dedicated separate components, the patent enables secure credential entry while minimizing the increase in device complexity. The same hardware infrastructure supports both original and new functions.
Solution Approach 2:
The system leverages the smart card's existing processing capabilities and capacitive sensing infrastructure to handle touch interface operations without requiring extensive additional control logic or external processing assistance. The card's embedded system self-manages the touch detection, sampling, and credential verification processes using its own resources, thereby limiting the complexity increase to only what is strictly necessary for the touch interface functionality.
3Measurement precision
If multi-channel touch sensors are supported, then touch position capturing accuracy is improved, but power consumption increases
Solution Approach 1:
The system implements selective activation of sensor channels based on operational requirements. Rather than continuously sampling all capacitive sensor channels at full resolution, the system activates only the necessary subset of channels and sampling rates required for the current task. This partial action approach maintains measurement precision when needed while avoiding the excessive power consumption that would result from full-channel continuous operation.
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 enables fast and accurate touch position capturing with reduced power consumption and supports multi-channel touch sensors, enhancing the security and usability of smart cards by allowing secure credential entry directly on the card.
Implementation Method 1
The electronic device comprises a first capacitor, a second capacitor, and an analog-to-digital converter. The first capacitor and the second capacitor are switchably coupled to each other; the first capacitor is switchably coupled to an input of the analog-to-digital converter.
Data Source
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AI summary
An electronic device (200, 300) for use in a touch-based user interface is provided, the electronic device comprising a first capacitor (108), a second capacitor (110), a third capacitor (202), and an analog-to-digital converter (104), wherein: the first capacitor and the second capacitor are switchably coupled to each other; the first capacitor is switchably coupled to an input of the analog-to-digital converter; the second capacitor is coupled to the input of the analog-to-digital converter; the third capacitor is coupled to the first capacitor; the third capacitor is switchably coupled to the second capacitor; the third capacitor is switchably coupled to the input of the analog-to-digital converter. A corresponding method of manufacturing an electronic device for use in a touch-based user interface is provided.