RFID Rectifier Voltage Limiter With Feedback Power Control

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Solution Overview

Problem

State-of-the-art RFID tags face challenges in protecting their integrated circuits from physical damage due to high power conditions when close to an RFID reader, leading to high-power dissipation and potential operational limitations, and lack effective anti-spy features to prevent intentional reading.

Innovation Solution

A voltage limiter for RFID ICs is introduced, featuring a current sink device and a reference generator with feedback circuitry that adjusts the reference voltage based on the current through the current sink device, effectively limiting power to the RFID IC and incorporating an additional current sink device and sensing mechanism to further control voltage levels, thereby preventing physical damage and enabling an anti-spy feature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a shunt limiter is connected to an nth stage of the rectifier to limit voltage, then the voltage is limited to a maximum level, but high power dissipation occurs through the limiter circuitry under near field conditions

Engineering Contradiction:

ImproveIC protection from physical damageVSAvoidpower dissipation through limiter circuitry

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent implements feedback circuitry that senses the current through the current sink device and adjusts the reference voltage accordingly. This feedback mechanism dynamically controls the current sink to limit power dissipation while maintaining voltage protection, resolving the contradiction between protecting the IC and minimizing energy loss in the limiter circuitry.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent transitions from a static shunt limiter to a dynamic voltage limiter using a current sink device whose operation is controlled by feedback circuitry. The system adapts its limiting behavior based on real-time conditions, enabling it to protect the IC while minimizing power dissipation under varying near-field conditions.

Inventive Principle:

Principle #15Dynamics

2Reliability

If limiter circuitry is included to protect the IC under high power conditions, then physical damage is prevented, but the performance and lifetime of the RFID tag IC are still impacted

Engineering Contradiction:

Improveprotection from physical damageVSAvoidlifetime of RFID tag IC

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The feedback circuitry continuously monitors the current through the current sink device and adjusts the reference voltage to maintain optimal limiting operation. This feedback control enables the limiter to protect the IC from damage while minimizing the impact on IC performance and extending its operational lifetime by preventing excessive power dissipation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the operating parameters of the limiter by using a voltage-controlled current sink instead of a fixed shunt connection. The reference voltage is dynamically adjusted based on feedback, allowing the system to adapt its protection level and minimize impact on IC lifetime while maintaining adequate protection.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If voltage limiter circuitry is added to protect the IC, then physical damage is reduced, but the device complexity increases

Engineering Contradiction:

Improvereduction of physical damageVSAvoidcomplexity of voltage limiter circuitry

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the voltage limiting function with the existing rectifier circuit by connecting the current sink device to the output of the RF rectifier and using feedback from the same circuit node. This integration approach reduces overall device complexity compared to adding a separate limiter stage, as the limiting function is merged with the power conversion circuitry.

Inventive Principle:

Principle #5Merging (Combining)

4Loss of energy

If feedback circuitry is added to vary the reference voltage based on current through the current sink device, then power limiting is strengthened, but device complexity increases

Engineering Contradiction:

Improvepower limiting effectivenessVSAvoidcomplexity of feedback circuitry

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The feedback circuitry senses the current through the current sink device and adjusts the reference voltage to maintain optimal power limiting. This feedback mechanism strengthens the power limiting effectiveness by dynamically adapting to changing conditions, while the implementation uses standard circuit components to minimize the increase in overall device complexity.

Inventive Principle:

Principle #23Feedback

Data Source

PatentEP4273749B1Voltage limiter for an RFID tag

Publication Date: 2025.01.08 NXP BV

Figure 1A~2
Figure 3A~3C
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AI summary

A voltage limiter (200) for a radio-frequency identification (RFID) integrated circuit (IC) for an RFID tag and a method for operating a voltage limiter is disclosed. The RFID IC includes a radio-frequency (RF) rectifier. The voltage limiter (200) comprises: a current sink device (210) coupled between an output (220) of the RF rectifier and ground (225); a reference generator (230) having an output (235) for providing a reference voltage (Vlim, 235) for controlling a current through the current sink device (210) to limit a voltage (Vrec) at the output (220) of the RF rectifier to values below a predefined voltage level; and feedback circuitry (240, 250) arranged to provide a feedback current to the reference generator (230) to vary the reference voltage (Vlim, 235), the feedback current being dependent on the current through the current sink device (210).