RFID Interrogator Noise Cancellation via Directional Coupler
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Solution Overview
Problem
RFID interrogators face challenges in accurately extracting tag signals due to undesirable reflections from the environment and interrogator components, which obscure the desired backscatter signal, leading to misreading or misidentification of RFID tags.
Innovation Solution
The use of a directional coupler and reflection circuitry to generate a phase-shifted and amplitude-adjusted canceling signal, which is combined with the received signal to cancel or diminish unmodulated reflections, thereby improving signal extraction quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the interrogator transmits a strong signal to power passive tags, then the tags can be powered and communicate, but the transmitter's continuous operation causes undesirable reflections that obscure the desired backscatter signal
Solution Approach 1:
The patent extracts the harmful reflected signal from the received signal by using a directional coupler to separate the forward and reflected components. The reflected signal is then cancelled through adaptive filtering, effectively removing the harmful interference from the detection path.
Solution Approach 2:
The patent introduces an intermediary canceling signal that is generated based on the transmitted signal and the detected reflected signal. This canceling signal is subtracted from the received signal to eliminate the harmful reflections, acting as a mediator between the transmitted signal and the desired backscatter signal.
2Object-affected harmful factors
If the interrogator uses a directional coupler and reflection circuitry to generate a canceling signal, then unwanted reflections are reduced, but the device complexity increases
Solution Approach 1:
The directional coupler serves multiple functions: it monitors the transmitted signal, detects the reflected signal, and provides the basis for generating the canceling signal. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in device complexity.
Solution Approach 2:
The system uses its own transmitted signal and detected reflected signal to generate the canceling signal, rather than requiring external calibration signals or additional reference sources. The adaptive filter automatically adjusts its parameters based on the detected reflections, making the system self-calibrating and reducing the need for manual intervention.
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 approach reduces unwanted reflections, enhancing the clarity of the received signal and improving the reliability and accuracy of RFID tag identification by isolating the tag signal from environmental and interrogator-induced noise.
Implementation Method 1
A directional coupler and reflection circuitry are used to generate a phase shifted, amplitude adjusted version of the transmit signal
Implementation Method 2
generate a phase shifted, amplitude adjusted version of the transmit signal
Implementation Method 3
generate a phase shifted, amplitude adjusted version of the transmit signal
Implementation Method 4
The canceling signal is combined with the received signal to cancel or diminish the unmodulated reflections
Data Source
AI summary
Methods and apparatuses for removing unwanted noise by a radio frequency identification (RFID) interrogator are provided. The interrogator transmits a transmitted signal while receiving a received signal. The received signal can include backscatter modulated signals from one or more RFID tags, as well as unmodulated reflections of the transmitted signal from the environment. The unmodulated reflections are undesirable and may make tag signal extraction difficult. A canceling signal is summed with the received signal to cancel or reduce the unmodulated reflections prior to tag signal extraction. In a specific embodiment, a phase shifted, amplitude adjusted reflection of the transmit signal is used by a directional coupler as the canceling signal.