| 摘要 |
<p>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 (f 0 ) 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.</p> |
