RF Voltage Limiter Circuit for RFID Antenna Overvoltage
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Solution Overview
Problem
UHF RFID transponders face overvoltage issues due to high levels of received antenna power, which can damage the integrated circuit, and existing RF limiters occupy a large chip area and consume excessive quiescent current.
Innovation Solution
A RF voltage limiter for UHF RFID transponders incorporating an envelope detector, peak detector, and shunt circuit to control the maximum voltage at the antenna, providing an area-efficient implementation with high discharge time to minimize signal envelope distortions and reduce quiescent current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive component-based peak detector with high discharge time is used, then overvoltage protection is improved, but chip area occupied increases significantly
Solution Approach 1:
The patent replaces the traditional mechanical/passive RC circuit-based peak detector with an active electronic circuit implementation using transistors (M1-M4), capacitors, and current sources. This substitution allows achieving the same peak detection and high discharge time function with significantly reduced chip area, as active circuits can provide higher impedance and longer discharge times without requiring large passive components.
Solution Approach 2:
The patent changes the operating parameters of the peak detector by using an active circuit configuration that provides a discharge time constant determined by the active impedance of the transistor circuit rather than passive RC values. The discharge time is controlled by the bias current and transistor characteristics, allowing for long discharge times (hundreds of microseconds) without occupying large chip area.
2Area of stationary object
If the discharge time of the peak detector is reduced, then chip area is reduced, but signal envelope distortions increase
Solution Approach 1:
By replacing the passive RC discharge mechanism with an active transistor-based discharge circuit, the patent achieves a discharge time constant that is decoupled from physical component sizes. The active circuit provides effectively infinite impedance during discharge, maintaining long discharge times and minimizing envelope distortions regardless of the small chip area used.
Solution Approach 2:
The patent introduces dynamic control of the discharge process through the active transistor circuit, which can adjust its effective impedance based on operating conditions. The bias current sources (IB1, IB2) provide dynamic control over the discharge rate, allowing optimization of the discharge time constant to match the signal modulation characteristics without requiring large fixed passive components.
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 RF voltage limiter effectively limits overvoltage conditions, minimizing signal distortions and reducing chip area requirements while maintaining efficient operation.
Implementation Method 1
The peak detector stage includes a current mirror acting as a rectifying buffer
Implementation Method 2
a shunt circuit coupled to provide an impedance to the antenna in response to the control signal, wherein the impedance decreases with an increasing voltage magnitude of the control signal
Implementation Method 3
an envelope detector having an input coupled to an antenna, the envelope detector configured to track an envelope of a signal received at the antenna
Data Source
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AI summary
A radio frequency (RF) voltage limiter for a radio frequency identification (RFID) transponder is provided. The RF voltage limiter includes an envelope detector configured to track an envelope of a signal received at the antenna. The envelope detector has an output for providing an envelope signal. A peak detector is included and has an input coupled to the output of the envelope detector. The peak detector includes a current mirror having an input coupled to the output of the envelope detector, and an output configured to provide a control signal. A shunt circuit is coupled to provide an impedance to the antenna in response to the control signal. The impedance decreases with an increasing voltage of the control signal to limit a maximum voltage at the antenna. In another embodiment, a method is provided for limiting a RF voltage at the antenna.