Switched Capacitor Power Supply for RFID Card Read Reliability
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Solution Overview
Problem
RFID cards with RF secure microcontrollers face issues with reduced current supply from the antenna coil at increased communication distances, leading to voltage fluctuations and read errors due to decreased current driving performance.
Innovation Solution
Incorporating a switched capacitor circuit that executes series charging and parallel discharging to maintain high current driving performance for the demodulator and internal circuits, even at extended communication distances, and adjusting current driving performance based on transmission signal data to reduce read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the communication distance between the card reader/card writer and the RFID card is increased, then the coverage area is improved, but the current from the antenna coil decreases leading to voltage fluctuations and read errors
Solution Approach 1:
The patent applies dynamics by making the current driving performance of the switched capacitor adjustable rather than fixed. The control circuit dynamically changes the current driving performance based on the communication distance, allowing the system to adapt to varying load conditions and maintain reliable operation at extended distances while preserving coverage area
Solution Approach 2:
The patent changes the parameter of current driving performance by controlling the effective load of the rectifying circuit. By adjusting the current driving performance of the switched capacitor through control circuits, the system can maintain stable voltage levels and reduce read errors even when operating at increased communication distances
2Stability of the object's composition
If the current driving performance of the switched capacitor is increased to maintain voltage stability, then the power supply stability is improved, but the magnetic field changes detected by the card reader decrease leading to read errors
Solution Approach 1:
The system dynamically adjusts the current driving performance based on communication distance rather than maintaining a fixed high performance. This allows the magnetic field changes to remain detectable by the card reader while still providing sufficient voltage stability for reliable operation at extended distances
Solution Approach 2:
The control circuit uses feedback from the communication distance information to adjust the current driving performance of the switched capacitor. This feedback mechanism ensures that the current driving performance is optimized for each specific communication scenario, maintaining both power supply stability and magnetic field detectability
3Stability of the object's composition
If a shunt regulator is used to reduce voltage fluctuations, then the power source voltage stability is improved, but the current driving performance for magnetic field detection decreases at increased distances
Solution Approach 1:
Instead of using a fixed shunt regulator, the patent employs a switched capacitor with controllable current driving performance. The control circuit adjusts the switched capacitor's performance based on communication distance, providing both voltage stability and sufficient current for magnetic field detection at extended distances
Solution Approach 2:
The patent changes the parameter of current driving performance by controlling the effective load of the rectifying circuit through the switched capacitor. This allows the system to maintain stable voltage levels while preserving enough current driving performance for reliable magnetic field detection even at increased communication distances
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
Ensures reliable operation of RFID cards at longer communication distances by maintaining high current driving performance and reducing read errors through effective load detection and adjustment.
Implementation Method 1
Power is supplied to the IC card by receiving an RF signal from a reader/writer called a card reader/card writer by an antenna coil of the IC card
Implementation Method 2
rectifying the RF signal by a rectifying circuit
Implementation Method 3
a change in the current of the antenna coil ANT can be detected as a change in the magnetic field of the antenna coil ANT by the card reader/card writer
Data Source
AI summary
A semiconductor integrated circuit has a rectifying circuit, a switched capacitor, a switched-capacitor drive circuit, a demodulator, and an internal circuit. The switched capacitor executes series charging and parallel discharging to/from a plurality of capacitors using an output rectified voltage. When the current driving performance at the time of supplying a power source voltage is set to a high state, so that a receiving operation in a card is executed reliably even at a long communication distance. Transmission signal data from a card is supplied to a switched-capacitor current driving performance increase disable circuit, and the current driving performance at the time of supplying the power source voltage in the switched capacitor is changed to be low. The change is detected as a magnetic field change in an antenna by an apparatus.