| 摘要 |
PROBLEM TO BE SOLVED: To prevent a modulation signal from being fluctuated in level when being outputted. SOLUTION: A signal generating means 21 outputs a reference signal Sr to be reference of the modulation signal to be changed with amplitude constant to a level varying means 24 only for a first period of time when the modulation signal is changed. Loop control is performed so as to make a detection output to the reference signal Sr equal to a level setting voltage, and an output of a first low-pass filter 29 at that time is held and stored as a first reference voltage Vr1. After the first period of time has passed and a changed modulation signal Sm is outputted, and when a second period of time has further passed, an output of a second low-pass filter 31 which has a large time constant and is hardly affected by modulation is held and stored as a second reference voltage. After that. a value obtained by adding a second error signal corresponding to difference between the second reference voltage and the output of the second low-pass filter 31 to the first reference voltage controls the gain or attenuation quantity of the level varying means 24. COPYRIGHT: (C)2005,JPO&NCIPI
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