Mode-Changeable Smart Card Power Circuit for Stable Load Modulation
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Solution Overview
Problem
The communication between a card reader and a smart card becomes unstable due to the operation of the voltage regulator in contactless smart card systems, which affects the reliability of the smart card system.
Innovation Solution
A mode-changeable power supply circuit for smart cards that includes a rectifier to convert AC voltage, a voltage regulator operating in low dropout (LDO) mode to maintain internal voltage stability, and a clamp circuit to connect the rectifier's output to ground, allowing the voltage regulator to switch between modes based on load modulation activation, thereby reducing noise and maintaining communication stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage regulator stabilizes the rectified voltage, then voltage regulation is achieved, but noise and distortion are introduced in the transmission signal
Solution Approach 1:
The voltage regulator dynamically adjusts its operation mode based on whether the load modulator is activated. During load modulation when transmission signals are present, the voltage regulator switches to a mode that minimizes noise and distortion generation. During non-modulation periods, it switches to a mode that provides strong voltage regulation. This dynamic adaptation eliminates the harmful noise and distortion while maintaining effective voltage regulation when needed.
Solution Approach 2:
The harmful noise and distortion generation is extracted or removed from the voltage regulator's operation during load modulation by switching to a special operation mode. The regulator controller detects the load modulator's activation state and accordingly switches the voltage regulator to a mode that excludes the noise-generating mechanisms from operation during critical transmission periods, while maintaining voltage regulation capability during non-critical periods.
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 mode-changeable power supply circuit effectively reduces noise and distortion in the transmission signal, enhancing the reliability and accuracy of communication between the card reader and smart card by maintaining a stable internal voltage and minimizing the impact of load modulation on the voltage regulator's operation.
Implementation Method 1
a rectifier to rectify a signal received through the antenna to output a rectified voltage
Implementation Method 2
The smart card converts an electromagnetic wave radiated from the card reader into a voltage signal through electromagnetic induction
Data Source
AI summary
A smart card includes an antenna to transmit and to receive a radio frequency signal, a rectifier to rectify a signal received through the antenna to output a rectified voltage, a voltage regulator to operate in a first operation mode for stabilizing a level of the rectified voltage and a second operation mode for generating an internal voltage using the rectified voltage, a regulator converter to control the voltage regulator to operate the voltage regulator in one of the first operation and the second operation according to a mode selection signal, a clamp circuit to connect an output terminal of the rectifier to a ground according to the mode selection signal, a load modulator to vary a resistance of the antenna to perform a load modulation, and a regulator controller to generate the mode selection signal according to whether the load modulator is activated or deactivated.