| 摘要 |
PURPOSE:To prevent a signal with an excessive level from being outputted even when an intermittent input signal is applied, by connecting a capacitor between the reference voltage input terminal of a differential amplifier and the ground and further connecting an electronic switch in parallel to the capacitor. CONSTITUTION:To a terminal 8, an input control signal 81 which has a high potential when a high-frequency input signal 11 is less than a prescribed threshold value (with a level as high as when no input signal arrives) or a low potential when not is applied. The electronic switch 10 consisting of a field effect transistor (FET) is closed (turning on the FET) when no signal is inputted to a terminal 1 to hold a reference voltage at 0 V, or opened (turning off the FET) when a signal is inputted to the terminal 1. Then, the reference voltage 61 rises gradually and a gain control signal corresponding to the rise minimizes the gain of a variable gain amplifier 3 to cause a gradual rise to a steady value corresponding to the input level. Therefore, an output signal 21 rises slowly and stabilizes itself at a prescribed level. |
