| 摘要 |
PURPOSE:To simplify the constitution by inserting a fixed attenuator when the relative attenuation is large and disconnecting it when the attenuation is small. CONSTITUTION:When the level of an input A is small and the relative attenuation is small, switches 4a-4d are turned off, the input enters a variable gain amplifier 1 and is amplified by a gain decided by an AGC voltage, detected and outputted at a detector 2. Furthermore, a part of the AGC voltage enters a comparator 6 and is compared with the threshold voltage Vh, and when the voltage is more than the Vh, the comparator 6 is operated, the switches 4a-4d are turned on, and the input A is fed to the amplifier 1 through a fixed attenuator 5. Thus, the constitution is simplified. |
