| 摘要 |
PURPOSE:To quicken the leading of a high frequency output signal by extracting equi-output points of an RF output with a base band signal or a phase signal set by a switch group sampling and holding an RF output detection value in the timing so as to control a mean output power. CONSTITUTION:A level of a high frequency (RF) output signal 6 subject to modulation is detected by an RF output power detection circuit 7. A sample-and- hold circuit 17 and a sample timing signal 23 are used to sample the level at a Nyquist point and to hold it till a succeeding Nyquist point. Then a difference between a mean power and a reference value is obtained at a differential amplifier 8 and the result is obtained by a feedback control signal 10 through an LPF 9. The feedback control signal 10 is fed back to a variable attenuator 16 provided before an RF power amplifier 5. In this case, when the mean output power is increased, the attenuation is increased and when the output is reduced, the attenuation is decreased thereby keeping the mean output power constant. |
