USB Clock Generator Without Crystal Oscillator for Smart Cards
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Solution Overview
Problem
Conventional smart card readers are expensive and slow due to their reliance on inaccurate RC oscillators, which are not suitable for the thin dimensions of smart cards, and the use of crystals is not feasible due to size and cost constraints, making it difficult to achieve the required clock accuracy for USB communication.
Innovation Solution
A clock signal generator that uses a control circuit to synchronize with sync signals, generate a frequency control signal, and produce a clock signal without a crystal oscillator, utilizing a current controller and oscillator to achieve high accuracy, suitable for both TX and RX clock signals in USB communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a crystal oscillator is used to achieve high clock accuracy for USB communication, then clock accuracy is improved, but device size and cost increase making it unsuitable for smart cards
Solution Approach 1:
The patent extracts the crystal oscillator from the system and replaces it with an RC oscillator combined with a frequency adjustment mechanism. The control circuit counts USB sync signals to determine the actual clock frequency and adjusts the RC oscillator's frequency accordingly, eliminating the need for a crystal oscillator while maintaining USB communication accuracy requirements
Solution Approach 2:
The patent changes the frequency parameter of the RC oscillator dynamically based on the counted sync signals from USB communication. By adjusting the frequency control signal according to the measured clock accuracy deviation, the system achieves required USB communication precision without relying on fixed-frequency crystal oscillators
2Measurement precision
If a crystal oscillator is used to achieve high clock accuracy, then clock accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive crystal oscillators with inexpensive RC oscillators. Although RC oscillators have lower inherent accuracy, the system compensates through software-based frequency adjustment using sync signal counting, achieving USB-compatible accuracy at much lower component cost
3Volume of moving object
If an RC oscillator is used in smart cards, then device size is reduced, but clock accuracy deteriorates to ±10%
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit continuously counts USB sync signals to measure the actual clock frequency deviation. Based on this feedback, the system adjusts the RC oscillator's frequency control signal to compensate for accuracy errors, maintaining USB communication precision while using compact RC oscillators
Solution Approach 2:
The patent replaces the mechanical/quartz crystal-based oscillation system with an electronic RC oscillation system controlled by digital frequency adjustment. The control circuit uses software algorithms to count sync signals and generate frequency control signals, substituting physical crystal resonance with electronic control
Data Source
AI summary
A clock signal generator for a USB device. The clock signal generator includes a control circuit and a clock generator that does not need to include a crystal oscillator. The control circuit counts the cycle of the clock signal during the period between two sync signals successively inputted, and generates a frequency control signal corresponding to the count value. The clock generator generates the clock signal with a frequency corresponding to the frequency control signal. The clock signal generator can generate a clock signal that is suitable for the data transfer rate defined, in the USB specification. In addition, the clock; signal generator can generate an RX clock signal so that an RX data signal can be recovered with its energy being stable.