RFID Transceiver Delay Circuit for Leakage Noise Cancellation

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Solution Overview

Problem

RFID transceiver devices face challenges in reducing receiver noise, especially at higher frequencies and longer distances, due to phase noise from leakage of transmission signals, which affects reception sensitivity and cannot be effectively addressed by existing solutions.

Innovation Solution

Incorporating a delay circuit between the local oscillation circuit and the demodulation circuit to equalize the path difference between the leakage and direct signal paths, and using a control and processing circuit to adjust the delay based on noise levels, ensuring that the impedance of the transceiving antenna matches the characteristic impedance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a duplexer is used to isolate transmission and reception signals, then transmission signal leakage is reduced, but phase noise from the leakage component still appears at the demodulation circuit output

Engineering Contradiction:

Improvetransmission signal leakageVSAvoidreception sensitivity

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent converts the harmful leakage signal into a beneficial component by deliberately introducing a delayed version of the transmission signal into the demodulation circuit. This delayed signal interferes destructively with the leakage component, canceling out the phase noise. The harmful leakage is thus transformed into a useful reference signal for noise cancellation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces a delay circuit as an intermediary element between the local oscillation circuit and the demodulation circuit. This delay circuit generates a delayed local oscillation signal that serves as a mediator to cancel the phase noise caused by transmission signal leakage, without requiring separate antennas or complex filtering systems.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If separate antennas are provided for transmission and reception, then signal isolation is improved, but device size and cost increase

Engineering Contradiction:

Improvesignal isolationVSAvoiddevice size

Core Design Contradiction:

Object-affected harmful factorsVSVolume of moving object

Solution Approach 1:

The patent merges the transmission and reception antenna functions into a single transceiving antenna. By combining these functions and using signal processing techniques (delay circuit and selective combining at the demodulation circuit), the patent achieves effective isolation without requiring physically separate antennas, thus reducing device size and cost.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent replaces the mechanical/physical solution of using separate antennas with an electrical/signal processing solution. Instead of physically isolating transmission and reception paths with separate antennas, the patent uses electronic delay circuits and signal combining techniques to achieve the same isolation effect, thereby reducing hardware complexity and device size.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Use of energy by moving object

If high transmission power is used to supply power to passive IC tags, then power source energy is sufficient, but transmission signal leakage increases causing saturation

Engineering Contradiction:

Improvepower source energyVSAvoidtransmission signal leakage

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of high-power transmission leakage into a useful reference signal. By deliberately introducing a delayed version of the high-power transmission signal into the demodulation circuit, the patent creates a reference that can be used to cancel the leakage component, allowing high transmission power to be used effectively without causing saturation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 configuration reduces noise levels and enhances reception sensitivity regardless of the distance to the tag, stabilizing the system in the UHF band and above, thereby achieving high sensitivity and reliability.

Implementation Method 1

a delay circuit between the local oscillation circuit and the demodulation circuit, the amount of delay of the delay circuit being set to a magnitude corresponding to the path difference between the path of the leakage through the duplexer into the demodulation circuit

Methodology Applied

Scientific EffectTime delay:

Implementation Method 2

a duplexer that supplies to a transceiving antenna the transmission signal from the transmission circuit and that branches the reception signal received by the transceiving antenna to the demodulation circuit

Methodology Applied

Scientific EffectSignal isolation:

Implementation Method 3

ensuring that the impedance of the transceiving antenna matches the characteristic impedance

Methodology Applied

Scientific EffectImpedance matching:

Data Source

PatentUS7492812B2RFID transceiver device

Publication Date: 2009.02.17 FUJITSU FRONTECH LTD

AI summary

An RFID transceiver device is capable of high sensitivity reception, by the reduction of noise, irrespective of the distance to the tag. The RFID transceiver device includes a delay circuit between a local oscillation circuit and a demodulation circuit, wherein the amount of delay of the delay circuit is set to a magnitude corresponding to the path difference between the path of leakage, via a duplexer into the demodulation circuit, of transmission signal output from the local oscillation circuit for transmission, and the path of direct input of the local oscillation signal from the local oscillation circuit to the demodulation circuit.