| 摘要 |
PURPOSE:To limit the output current of a power amplifier and increase the speed of response to the fluctuation of load impedance, by inserting a lambda/4 circuit between the power amplifier and the load and then providing an amplitude limiting circuit that limits the output voltage of the lambda/4 circuit. CONSTITUTION:A lambda/4 circuit 45 is inserted between the power amplifying circuit 43 and the output tuning circuit 46, and the input impedance has a fluctuation for the circuit 46 as the load impedance of the output terminal 50 has a fluctuation. As a result, the load impedance of circuit 45 also has a fluctuation. The high frequency transformer 47 and diode 48 form a high frequency rectifying circuit which functions as an amplitude limiting circuit. When the output voltage of the rectifying circuit is lower than the modulated voltage of terminal 41, the diodes 481 and 482 are cut off to give virtually no effect to the high frequency circuit. On the contrary, the output voltage of the said rectifying circuit is limited by the modulated voltage although the output voltage of circuit 45 is going to increase. Thus the input voltage of transformer 47, i.e. the output voltage of circuit 45 is limited. In other words, the output current of amplifier 43 is limited. |
