RF Transmitter Circuit for Short-Antenna Bandwidth Switching
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Solution Overview
Problem
Existing RF transmitters with electrically short antennas face challenges in dynamically altering bandwidth without subjecting electronic switch elements to high voltages, leading to reduced efficiency and shortened lifespan.
Innovation Solution
An RF transmitter design that uses a capacitive energy storage and a switching circuit with a transistor to alter the series resistance of the switching circuit in its closed state, allowing temporary changes to the quality factor of the resonance circuit without adding dedicated loss resistances or switches to the antenna terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electronic switch elements are connected directly to antenna terminals to alter bandwidth, then bandwidth can be dynamically changed, but the switches are subjected to high voltages that damage them or shorten their lifespan
Solution Approach 1:
The patent introduces an intermediary capacitor between the electronic switch element and the antenna terminal. This capacitor acts as a voltage-blocking barrier that allows the switch to control the resonant circuit's bandwidth while being protected from the high voltages present at the antenna terminal. The capacitor couples the switch to the resonant circuit while isolating it from damaging voltage levels.
2Loss of energy
If resistive losses are reduced in the antenna and associated circuits to increase efficiency, then power efficiency improves, but the quality factor (Q) of the antenna increases causing bandwidth to decrease
Solution Approach 1:
The patent employs a dynamic bandwidth control mechanism using electronic switch elements that can temporarily alter the resonant circuit's quality factor. By switching in or out of the resonant circuit additional capacitive or inductive elements, the system can dynamically adjust the bandwidth to match communication requirements while maintaining low resistive losses for high efficiency operation during normal transmission.
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 a compact transmitter design with high power efficiency and avoids the disadvantages of prior art by controlling the quality factor and resonance frequency without exposing switches to high voltages, thus extending their lifespan.
Implementation Method 1
The capacitive energy storage is adapted to form with the electrically short antenna when connected thereto a resonance circuit with a resonance frequency and a quality factor
Implementation Method 2
allowing temporary changes to the quality factor of the resonance circuit by changing the series resistance of the switching circuit in its closed state
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention is 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). The transmitter (1) comprises a capacitive energy storage (2), an output stage (31,32) and a switching circuit (9) with an open state and a closed state. The capacitive energy storage (2) is adapted to form with the antenna (100) when connected thereto a resonance circuit (2,100) with a resonance frequency (f0) and a quality factor (Q). The output stage (31,32) is adapted to provide an electric transmission signal to the resonance circuit (2, 100). The switching circuit (9) comprises a first transistor (24,25,311,312) for switching between the open state and the closed state and is connected to an antenna output terminal (10,11) through a capacitance (21,23,33,34) formed by the capacitive energy storage (2) such that the maximum signal voltage occurring across the switching circuit (9) in its open state is lower than the maximum signal voltage occurring across the antenna output terminals (10,11). In order to allow temporarily altering the bandwidth of the resonance circuit (2,100), the transmitter (1) is adapted to alter the quality factor (Q) by changing the series resistance of the switching circuit (9) in its closed state.