| 摘要 |
PURPOSE:To function a saturation prevention control loop only when the size of an output signal is larger than a reference signal by providing a switch operating by the state of a signal transmitting in the saturation prevention control loop of a RF power amplifier itself on the loop. CONSTITUTION:The part of the output power of a signal to be modulated which is outputted from a RF power amplifier 3 is coupled by a directional coupler 7 and is detected by a detection circuit 6, and the size of the DC voltage component is detected. When the DC voltage component of the signal to be modulated which is outputted from the detection circuit 6 becomes larger than reference voltage, the output from the output terminal 8OUT of a comparator 8 changes from an H to L. As a result, a switch 9 becomes a conductive state and the L output of the size according to the difference of reference voltage and the DC voltage component of the signal to be modulated is impressed on an adder 10. Because the L output from the comparator 8 is a negative value, the size of a signal to be inputted in a gain control terminal 2c is lowered and also the gain of a gain variable amplifier 2 is reduced according to the size. |
