Smartcard RF Switching Circuit for Biometric NFC Blocking
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Solution Overview
Problem
Existing RF switches for smartcards are unable to meet the cost, power rating, frequency of operation, and height constraints required for secure and robust control of near field RF communications, particularly in biometric authentication systems, and existing solutions like injecting noise into the communication system are expensive and insufficiently robust.
Innovation Solution
An RF switching apparatus with novel transistor-level designs, including a splitter and a switching arrangement, divides the RF signal to inhibit or enable near field RF communications based on biometric authentication, using auxiliary circuits and RF switches with selective impedance matching and inductive coupling to manage power distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noise injection is used to block RF communications until biometric authentication is complete, then security is improved, but cost increases and robustness is insufficient
Solution Approach 1:
An RF switch is introduced as an intermediary component between the NFC antenna and the NFC controller. This switch acts as a physical mediator that can selectively connect or disconnect the RF communication path, providing robust security control without requiring expensive noise injection circuits. The switch is controlled by authentication logic to enable or disable RF communications based on biometric verification status.
2Device complexity
If a DC switch is used to control RF communications, then simplicity is improved, but it cannot effectively block RF signals
Solution Approach 1:
The patent transitions from using a DC switch (which operates at direct current levels) to an RF switch (which operates at radio frequency levels). This parameter change in the operating frequency enables the switch to effectively control RF signal paths. The RF switch maintains relative simplicity while providing the necessary signal blocking capability through its design optimized for RF frequencies, including appropriate impedance matching and switching mechanisms.
3Ease of manufacture
If commercially available RF switches are used, then ease of manufacture is improved, but they cannot meet the height constraint of under 350um
Solution Approach 1:
The patent specifies critical dimensional parameters for the RF switch, including a maximum height of 350 micrometers and an active area not exceeding 1.5mm x 1.5mm. These parameter constraints drive the selection and design of suitable RF switch implementations that can be integrated within the smart card form factor while maintaining electrical performance.
4Length of stationary object
If diebond manufacturing is used to meet RF switch height constraints, then height requirement is satisfied, but manufacturing cost increases
Solution Approach 1:
The patent establishes a height constraint of under 350um for the RF switch to ensure compatibility with smart card manufacturing processes. This parameter enables the use of standard manufacturing techniques while still achieving the necessary miniaturization for card integration, avoiding the need for more expensive diebond processes.
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
Provides secure and robust control of near field RF communications in smartcards by ensuring the RF chip remains inactive until authentication is complete, enhancing security and reducing manufacturing costs through efficient power management.
Implementation Method 1
a near field RF communications interface for powering the IC and providing data communications to and from it
Implementation Method 2
a switching arrangement connected to the near field RF communications chip and selectively operable to disable said provision of the RF electrical signal to the chip thereby to inhibit the near field RF communications chip from performing near field RF communications
Data Source
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AI summary
A smartcard circuit for control of a near field RF communications chip (500) of a smartcard (2000) is described. The circuit comprises a primary inductive coupler (1003) for connection to a near field antenna (2002) of a smart card for obtaining an RF electrical signal from the antenna, and a secondary inductive coupler (1005) arranged for inductive coupling with the primary inductive coupler and connected to the chip for provision of the RF electrical signal from the primary inductive coupler to enable the chip to perform near field RF communications for the smartcard. The disclosure also provides switching circuitry (528) coupled to the secondary inductive coupler and comprising an RF conduction path selectively operable to disable said provision of the RF electrical signal thereby to inhibit the chip from performing near field RF communications. Advantageously the RF conduction path generally is controlled by a transistor (110) having a drain connected to one plate of at least one capacitor in the RF conduction path wherein a one-way conduction path is arranged so that transmission of RF signal along the RF conduction path causes accumulation of an electrical charge on the one plate of the at least one capacitor via the one-way conduction path.