Rectifier Limiter Circuit with Multiple Time Constants for RFID Tags
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Solution Overview
Problem
Passive RFID tags face issues with voltage-withstanding reliability, reception saturation, and reduced read-write distance due to varying electromagnetic energy levels, leading to transistor damage and communication failures.
Innovation Solution
A rectifier and limiter circuit with multiple time constants, featuring a resonant capacitor and inductor, and two discharge paths controlled by distinct control circuits with different time constants, allowing for controlled voltage adjustment and proper discharge management to prevent saturation and enhance communication range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the passive RFID tag is placed closer to the card reader or the electromagnetic energy is increased, then the demodulation capacity and communication quality are improved, but the voltage exceeds the transistor's withstanding limit causing damage
Solution Approach 1:
The patent applies preliminary anti-action by introducing a limiter circuit that preemptively clamps the voltage to a safe level before it can damage the transistor. The limiter circuit detects when voltage approaches the transistor's withstanding limit and actively prevents further voltage increase, thus protecting the transistor from damage while allowing the system to operate at higher power levels for improved communication quality.
Solution Approach 2:
The patent uses an intermediary approach by inserting a limiter circuit between the rectifier output and the transistor input. This intermediary component absorbs and limits excessive voltage, acting as a buffer that protects the transistor from voltage spikes while allowing the rectifier to operate at higher power levels for better demodulation capacity.
2Use of energy by moving object
If the passive RFID tag is placed closer to the card reader, then the electromagnetic energy absorption is improved, but the load modulation signal causes saturation at the card reader receiving end
Solution Approach 1:
The patent applies dynamics by implementing a discharge path controlled by a control circuit that dynamically adjusts its operation based on real-time voltage conditions. When voltage exceeds a threshold, the discharge path is activated to release excess energy; when voltage is within limits, the discharge path remains inactive. This dynamic control allows the system to operate at high power levels for improved energy absorption while preventing harmful effects like reception saturation.
Solution Approach 2:
The patent uses feedback control by monitoring the voltage at the rectifier output and using this information to control the discharge path. The control circuit continuously detects voltage levels and adjusts the discharge path operation accordingly, creating a closed-loop system that maintains voltage within safe limits while maximizing energy absorption capability.
3Loss of energy
If the card reader stops sending energy during uplink communication to save power, then the energy consumption is reduced, but the tag cannot complete command demodulation and uplink communication
Solution Approach 1:
The patent applies preliminary action by having the card reader send energy during the downlink phase to charge the tag's energy storage circuit before uplink communication begins. This preliminary energy transfer ensures that the tag has sufficient stored energy to complete both command demodulation and uplink communication without requiring continuous energy transmission from the card reader, thus reducing overall energy consumption while maintaining communication reliability.
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 solution effectively manages voltage levels, prevents transistor damage, and increases the read-write distance of passive RFID tags by ensuring proper energy handling and demodulation capacity.
Implementation Method 1
a resonant capacitor, which is connected, between a first antenna terminal and a second antenna terminal, in parallel to a resonant inductor, and configured to form a resonant circuit together with the resonant inductor, receive an external electromagnetic field and couple the external electromagnetic field to a rectifier circuit
Implementation Method 2
a rectifier circuit, the input terminal of which is connected to the first antenna terminal and the second antenna terminal and configured to convert AC power, to which the resonant circuit is coupled, into DC power
Data Source
AI summary
The present invention relates to the technical field of radio frequency identification, in particular to a rectifier and limiter circuit having a plurality of time constants and a passive radio frequency tag containing this rectifier and limiter circuit. By applying analog control signals with different time constants to control terminals of two discharge paths of the rectifier and limiter circuit, respectively, i.e., adjusting the voltage amplitude at different switching speeds, switching the two discharge paths from a completely open state to a completely closed state is realized. Discharging is performed properly according to the amount of charge at antenna terminals and the level of energy of the tag, thus to improve the demodulation capacity of the tag and increase the read-write distance of the tag.