Biometric Smart Card Clock Alignment for Sensor Noise Reduction
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Solution Overview
Problem
Smart cards using biometric authentication experience reduced reliability due to noise generated when the frequency of the external clock signal from the card reader is an odd-numbered multiple of the sensor clock signal, affecting sensor performance.
Innovation Solution
The smart card design includes a frequency measurement circuit to align the sensor clock signal with an even-numbered multiple of the external clock signal, using a sensor clock output circuit to generate a sensor clock signal with a specific frequency range, and a sensor circuit to output sensing data based on compensation image data, minimizing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the smart card uses an external clock signal from the card reader for communication, then the communication functionality is improved, but noise is generated in the sensor clock signal when the external clock frequency is an odd-numbered multiple of the sensor clock frequency, reducing reliability
Solution Approach 1:
The patent changes the frequency parameter of the sensor clock signal by selecting from multiple predetermined frequency ranges (e.g., 1-2.5MHz, 2.5-5MHz) based on the measured external clock frequency. This parameter adjustment ensures that the sensor clock frequency and external clock frequency do not have an odd-numbered multiple relationship, thereby eliminating noise generation while maintaining communication functionality.
Solution Approach 2:
The patent implements a feedback mechanism where the frequency measurement circuit continuously monitors the external clock signal frequency and provides this information to the sensor clock output circuit. The sensor clock output circuit then adjusts the sensor clock frequency accordingly based on this feedback, creating a closed-loop system that prevents noise generation while adapting to different external clock conditions.
2Reliability
If the sensor clock signal frequency is adjusted to avoid odd-numbered multiple relationships with the external clock signal, then noise reduction and reliability improvement are achieved, but the device complexity increases due to frequency measurement and selection circuits
Solution Approach 1:
The patent segments the frequency adjustment function by dividing the possible sensor clock frequencies into multiple predetermined ranges. Instead of continuously adjusting the frequency, the system selects from discrete frequency ranges (e.g., 1-2.5MHz, 2.5-5MHz), which simplifies the required circuitry while still achieving noise reduction. This segmentation approach reduces the complexity compared to continuous frequency tuning.
Solution Approach 2:
The patent applies partial action by only adjusting the sensor clock frequency when necessary (i.e., when the external clock frequency indicates potential noise generation). The system measures the external clock frequency and only changes the sensor clock frequency if needed, rather than continuously adjusting it. This selective adjustment reduces the complexity of the control logic while maintaining reliability.
Data Source
AI summary
A smart card includes a frequency measurement circuit configured to measure a first clock frequency of an external clock signal, a sensor clock output circuit configured to select a first range from a plurality of first clock ranges based on the first clock frequency and to output a sensor clock signal having a second clock frequency corresponding to the first range, and a sensor circuit configured to output sensing data for biometric authentication based on the sensor clock signal and first compensation image data.