Pulse Density RFID Transmitter for Stable Antenna Power
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Solution Overview
Problem
Existing RFID transmitters face issues with electromagnetic interference and power consumption due to the interaction between the electromagnetic interference filter and the RFID antenna, particularly in applications like NFC wireless charging, where fluctuations in resonance occur due to proximity objects, and switched capacitor losses are high.
Innovation Solution
Implementing pulse density modulation with a delta-sigma modulator or a stored lookup table to generate a transmitter signal, which moves noise away from the carrier frequency, reducing the need for close filter poles and minimizing power fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electromagnetic interference filter uses a corner frequency close to the carrier frequency to reduce harmonics, then the sinusoidal output signal quality is improved, but the filter poles and antenna resonate at close frequencies causing interaction and power fluctuations when objects move in proximity
Solution Approach 1:
The patent introduces pulse density modulation as an intermediary technique between the digital baseband signal and the RF carrier. By modulating the carrier density rather than amplitude or frequency directly, the system achieves sinusoidal output quality without requiring the EMF filter poles to be close to the carrier frequency, thereby eliminating the harmful interaction between filter and antenna resonance
Solution Approach 2:
The patent changes the modulation parameter from traditional amplitude or frequency modulation to pulse density modulation. This parameter change allows the EMF filter to be positioned at a different frequency relationship to the carrier, specifically where the corner frequency does not need to be close to the carrier frequency, thus avoiding resonance interaction while maintaining signal quality
2Ease of operation
If traditional amplitude modulation is used to transmit digital data as analogue signal, then communication with tags is achieved, but power consumption increases due to switched capacitor losses in the power amplifier
Solution Approach 1:
The patent replaces the traditional amplitude modulation mechanism with pulse density modulation. Instead of varying the amplitude of the carrier signal to encode digital data, the system varies the density of pulses, which reduces switched capacitor losses in the power amplifier while maintaining the ability to communicate digital data to tags
Solution Approach 2:
The patent employs periodic pulse density modulation where the carrier signal is transmitted in periodic pulse trains with varying density. This periodic action allows digital data to be encoded through pulse density variations over time, achieving communication functionality with reduced power consumption compared to continuous amplitude modulation
3Productivity
If the RFID antenna is tuned to resonate at carrier frequency for maximal power output, then wireless charging efficiency is improved, but resonance changes when objects move in proximity causing output power fluctuations
Solution Approach 1:
The patent introduces pulse density modulation as an intermediary that decouples the relationship between filter poles and antenna resonance. By doing so, the antenna can maintain stable resonance at the carrier frequency for maximal wireless charging efficiency without being adversely affected by filter-induced power fluctuations when objects move in proximity
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 enhances energy transfer efficiency, reduces power consumption, and stabilizes output power in the presence of proximity objects, while maintaining effective communication and charging capabilities.
Implementation Method 1
an electromagnetic interference filter built to filter the amplified transmitter signal and built to provide a filtered transmitter signal
Implementation Method 2
a matching circuit connected to the electromagnetic interference filter and the RFID antenna and built to match their impedances
Implementation Method 3
The reader is powered and generates a magnetic field emitted by its RFID antenna. When the reader and the tag are within close proximity of each other, the reader generated magnetic field is induced into the RFID antenna of the tag and used to power the passive tag
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A transmitter (19; 36) built to drive an RFID antenna (20) of the transmitter (19; 36) with an antenna signal (21) with a substantial sinusoidal current/voltage and a carrier frequency in the RFID frequency range of 100kHz to 100MHz, which transmitter (19; 36) comprises: a power amplifier (22) built to provide an amplified transmitter signal (23) and an electromagnetic interference filter (33) built to filter the amplified transmitter signal (23) and built to provide a filtered transmitter signal (34) and a matching circuit (35) connected to the electromagnetic interference filter (33) and the RFID antenna (20) and built to match their impedances and built to receive the filtered transmitter signal (34) and built to provide the antenna signal (21) to the RFID antenna (20), wherein that the transmitter (19; 36) comprises a transmitter signal source (25; 37) connected to the power amplifier (22) and built to provide a pulse density modulated signal as transmitter signal (26) to the power amplifier (22).