RF Communications Device EMI Reduction via Automatic Gain Control

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Solution Overview

Problem

Electromagnetic interference (EMI) from RF communications devices such as RFID/NFC tags and active powered NFC controller ICs is a concern due to the rectification of currents induced in the antenna, which can produce unwanted emissions within the RF spectrum.

Innovation Solution

The RF communications device incorporates an automatic gain controller, a rectifier, and a voltage limiter. The automatic gain controller modulates the current from the antenna, reducing the current entering the rectifier, which in turn minimizes unwanted emissions. The voltage limiter diverts a portion of the rectified current, producing a control signal to adjust the automatic gain controller, ensuring optimal current management and reduced EMI.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If high currents are required to pass through the rectifier to power the RF communications device, then the device can operate with sufficient power, but high levels of Electromagnetic Interference (EMI) are produced which may violate ETSI limits and interfere with device operation

Engineering Contradiction:

Improvepower supply to RF communications deviceVSAvoidElectromagnetic Interference (EMI)

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The current path is segmented into multiple branches: a first current path through the rectifier for power generation, and a second current path through the automatic gain controller for signal processing. This segmentation allows current to be diverted away from the rectifier, reducing EMI while maintaining sufficient power supply through the first path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The automatic gain controller acts as an intermediary component that provides an alternative current path. By introducing this intermediate element, the system can control the amount of current passing through the rectifier, thereby reducing EMI emissions while still delivering adequate power to the RF communications device.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If the antenna introduces field-strength dependent current into the system, then the device can harvest energy from the RF field, but the internal voltage may exceed the limits of the process technology used to manufacture the device

Engineering Contradiction:

Improveenergy harvesting from RF fieldVSAvoidvoltage within process technology limits

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The voltage regulation function is segmented from the rectifier and implemented through a dedicated voltage limiter circuit. This separate voltage limiting path monitors and controls the voltage level independently, ensuring it remains within process technology limits while allowing the rectifier to continue harvesting energy from the RF field.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The voltage limiter provides feedback control by monitoring the rectified voltage and adjusting the current distribution accordingly. When voltage approaches dangerous levels, the system automatically diverts more current through the automatic gain controller path, preventing voltage excursions that could damage the device.

Inventive Principle:

Principle #23Feedback

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 effectively reduces EMI emissions by modulating the current entering the rectifier and optimizing the power supply to the RF communications device, thereby ensuring compliance with ETSI limits and improving device operation.

Implementation Method 1

an automatic gain controller coupled to the antenna terminals for receiving an output current of the antenna, wherein the automatic gain controller is operable to convert the output current of the antenna into a modulated current

Methodology Applied

Scientific EffectAutomatic gain control:

Implementation Method 2

a rectifier coupled to the automatic gain controller to receive the modulated current, wherein the rectifier is operable to convert the modulated current into a rectified current

Methodology Applied

Scientific EffectRectification:

Implementation Method 3

a voltage limiter coupled to the rectifier for receiving the rectified current, wherein the voltage limiter is operable to convert the rectified current into a limited rectified voltage for supplying power to the RF communications device

Methodology Applied

Scientific EffectVoltage limiting:

Data Source

PatentUS20250200319A1RF communications device with EMI reduction

Publication Date: 2025.06.19 NXP BV

AI summary

A Radio Frequency (RF) communications device includes a pair of antenna terminals, which are connectable to an antenna. The device also includes an automatic gain controller, which is coupled to the antenna terminals for receiving an output current of the antenna. The automatic gain controller is operable to convert the output current of the antenna into a modulated current. The device further includes a rectifier, which is coupled to the automatic gain controller to receive the modulated current. The rectifier is operable to convert the modulated current into a rectified current. The device also includes a voltage limiter, which is coupled to the rectifier for receiving the rectified current. The voltage limiter is operable to convert the rectified current into a limited rectified voltage for supplying power to the RF communications device. An RF identification (RFID) tag comprising the RF communications device is also disclosed.