| 摘要 |
It is an object of the present invention to provide a transmitter which is inexpensive and small in size and is reduced in power dissipation and besides wherein the output power of a power amplifier can be varied to an arbitrary value. A phase modulator, a variable attenuator, a high power amplifier, a directional coupler, a detector, an error amplifier, a switch and an analog multiplier form an envelope feedback loop. The envelope feedback loop controls an envelope of a modulated wave detected by the detector so that a base band signal and the envelope of the modulated wave may coincide with each other. The circuits mentioned above, a smoothing circuit, another error amplifier, another switch and an adder form an operation point feedback loop. The operation point feedback loop smoothes an error of an output envelope detection signal of the detector and controls so that the smoothed error may be in the minimum. Accordingly, with the transmitter of the present invention, even if a variation of the gain of the high power amplifier or the like occurs, a reference amplitude signal for the envelope feedback loop to be inputted from a rectifier to the error amplifier is controlled by an ALC loop which feeds back the reference amplitude signal so that a smoothed level of a root mean square value of the envelope detection signal and a first reference voltage may coincide with each other, and a fixed output power corresponding to the first reference voltage is obtained at an output terminal. <IMAGE> |
