RFID Transponder PLL Clock Generation
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Solution Overview
Problem
RFID transponders face limitations in cost, complexity, and applicability due to the need for internal crystal oscillators for determining signal lengths, and LC oscillators have restricted Q range and maintenance issues for broadband and short-distance data transmission.
Innovation Solution
An RFID transponder design incorporating a class C amplifier with a resonant circuit, a controllable pulse width generator, and a phase locked loop (PLL) that generates an internal clock signal to maintain oscillation without external excitation, allowing for broader applicability and reduced costs by eliminating the need for internal crystal oscillators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an internal crystal oscillator is used to generate clock signals for determining signal lengths, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the clock signal generation function from a separate crystal oscillator and integrates it into the PLL circuit. The PLL generates its own internal clock signal by locking to the received RF signal, eliminating the need for a separate crystal oscillator while maintaining the ability to accurately measure signal lengths and off-periods
Solution Approach 2:
The PLL circuit serves multiple functions: it locks to the received RF frequency for frequency synthesis, generates the internal clock signal for timing measurements, and provides the reference frequency for the Class C amplifier. This multi-functionality replaces what would traditionally require separate crystal oscillator and frequency synthesis circuits
2Ease of manufacture
If an LC-oscillator is used instead of a crystal oscillator, then device cost is reduced, but reliability and Q range are limited
Solution Approach 1:
The patent employs a dynamic approach where the PLL continuously adjusts and locks to the received RF frequency, allowing the system to adapt to different operating conditions and Q ranges. The Class C amplifier dynamically plucks the resonant circuit at the correct phase and frequency determined by the PLL, ensuring reliable oscillation maintenance across varying conditions rather than relying on a fixed-frequency crystal oscillator
Solution Approach 2:
The PLL acts as an intermediary between the received RF signal and the internal clock generation. It translates the external RF frequency into a stable internal clock signal that can be used for timing measurements, bridging the gap between the variable Q resonant circuit and the precise timing requirements
3Device complexity
If the resonant circuit oscillation is used as reference clock signal, then device complexity is reduced, but adaptability for broadband transmission is limited
Solution Approach 1:
The PLL provides dynamic frequency tracking and synthesis capabilities that allow the transponder to adapt to different frequency bands and transmission conditions. The PLL can lock to various RF frequencies and generate corresponding internal clock signals, enabling broadband operation while keeping the overall device complexity low by using the existing resonant circuit
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
This solution enables continuous operation of the transponder with improved Q range and reduced costs, enhancing its applicability and efficiency in data transmission without requiring internal crystal oscillators.
Implementation Method 1
The antenna or resonant circuit is then excited by an external RF wave. If the external excitation stops, the oscillation of the antenna (resonant circuit) dies out.
Implementation Method 2
Another approach consists of using an LC-oscillator (also LC-tank or resonant circuit). These types of oscillators are cheap.
Implementation Method 3
The PLL is configured to be locked to an RF signal received through the antenna (i.e. the resonant circuit) and to be switched into a free running mode when the PLL is locked to the input RF frequency.
Implementation Method 4
Class C amplifiers contain a LC tank or resonant circuit and a plucking device (e.g. a transistor), which is periodically switched on and off for a short time. In this way, the resonant circuit is actively triggered to continue oscillating.
Implementation Method 5
The controllable pulse width generator is connected to an internal oscillator to periodically switch the plucking device on and off so as to maintain an oscillation of the resonant circuit.
Data Source
AI summary
An RFID transponder comprises an antenna for receiving data in a downlink mode and transmitting data in an uplink mode, with a modulation stage for modulating uplink data and a demodulation stage for demodulating downlink data. A class C amplifier is provided, which has a resonant circuit, a plucking device coupled to the resonant circuit, and a controllable pulse width generator coupled to the plucking device. The controllable pulse width generator is adapted to periodically switch the plucking device on and off so as to maintain an oscillation of the resonant circuit. The transponder further comprises a phase locked loop configured to be locked to an oscillating signal received through the antenna and to be switched into a free running mode without being locked to the oscillating signal received through the antenna, thereby being adapted to output an independent internal clock signal for the RFID transponder.