| 摘要 |
PROBLEM TO BE SOLVED: To prevent the output of an amplifier from being excessively increased by erroneous gain control in the case of an abnormality in level detection. SOLUTION: When gain control processing 102 by control cycle is terminated, control for changing the attenuation rate of a variable attenuator is performed during the gain control processing. In this case, output level detection values Lout and Lout0 after the control and after the preceding control and output target levels Lt and Lt0 corresponding to input level detection values are fetched. Then examination is performed relative to a second condition whether ¾Lout-Lout0¾ is not less than a prescribed value or not and a first condition that the sign of ((Lt-Lout)-(Lt0-Lout0)) is minus in controlling the increase of the attenuation rate or the sign of ((Lt-Lout)-(Lt0-Lout0)) is plus in controlling the decrease of the attenuation rate. When the attenuation rate is controlled in the continuous N-times of control cycles and also at least one of the first and second conditions is not established, the abnormality is defined in a gain control system, so as to stop the gain control. COPYRIGHT: (C)2007,JPO&INPIT
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