RF Transmitter Circuit for Short Antenna Bandwidth Tuning
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Solution Overview
Problem
Existing RF transmitters with electrically short antennas face challenges in efficiently transmitting electromagnetic signals due to low radiation resistance and bandwidth limitations, as they require dynamic changes in resonance frequency and quality factor, which can damage electronic switch elements when subjected to high voltages.
Innovation Solution
An RF transmitter design that alters the quality factor of the resonance circuit by changing the series resistance of the switching circuit, controlled by a gate voltage applied to a transistor, allowing temporary bandwidth adjustment without adding dedicated loss resistances or switches to antenna terminals, thus maintaining high power efficiency and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electronic switch elements are connected directly to antenna terminals to change resonance frequency, then bandwidth can be adjusted dynamically, but the switch elements are damaged by high voltages at antenna terminals
Solution Approach 1:
The patent introduces voltage dividers formed by serially connected capacitors as intermediary elements between the electronic switch elements and antenna terminals. These capacitors divide the high voltage at the antenna terminals, protecting the switch elements from voltage damage while still allowing them to control the resonance frequency and bandwidth dynamically.
2Adaptability or versatility
If resistive loads are added to antenna terminals to increase bandwidth, then bandwidth is temporarily increased, but switch elements are subjected to large signal voltages that could damage them
Solution Approach 1:
The patent places voltage dividers (serially connected capacitors) between the resistive loads and antenna terminals, and between the electronic switch elements and antenna terminals. This intermediary structure protects both the switch elements and resistive loads from high voltage stress while allowing the resistive loads to effectively increase bandwidth when activated.
Solution Approach 2:
The patent dynamically changes the resistance parameter at the antenna terminals by switching resistive loads in and out of the circuit. This parameter change allows temporary bandwidth increase without permanently degrading the antenna system, and the voltage dividers ensure these parameter changes don't expose components to damaging voltages.
3Loss of energy
If quality factor is increased to reduce resistive losses, then antenna efficiency is improved, but bandwidth decreases
Solution Approach 1:
The patent makes the quality factor and bandwidth parameters dynamic rather than fixed. By using electronic switch elements controlled by information signals, the system can dynamically adjust the quality factor to match the instantaneous frequency requirements, allowing high efficiency at the center frequency while providing extended bandwidth when needed through controlled Q-factor reduction.
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
Enables efficient transmission of electromagnetic signals with adjustable bandwidth and resonance frequency, protecting electronic components from high voltages and achieving robust, high-efficiency operation in compact designs for portable devices like hearing aids.
Implementation Method 1
The capacitive energy storage (2) is adapted to form with the antenna (100) when connected thereto a resonance circuit with a resonance frequency and a quality factor
Implementation Method 2
The transmitter is adapted to alter the quality factor by changing the series resistance of the switching circuit in its closed state
Implementation Method 3
controlled by a gate voltage applied to a transistor, allowing temporary bandwidth adjustment
Implementation Method 4
The electric transmission signal is frequency- and/or phase-modulated with an information signal and thus has an instantaneous frequency that varies in dependence on the information signal
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention is based on an RF transmitter (1) with two antenna output terminals (10, 11) for connecting to corresponding antenna terminals (101, 102) of an electrically short antenna (100) for transmission of an electromagnetic signal (TX).