| 摘要 |
PURPOSE:To obtain an AGC circuit which becomes an IC easily has a good characteristic, by controlling a variable gain circuit according to the level difference of DC components in the input and the output of an AM detector. CONSTITUTION:In the AGC circuit which controls the gain of circuit 2 by the output of AM detector circuit 4 coupled with the output of variable gain circuit 2, a reference voltage supply is removed, and in stead of it, DC components are taken out from the input of AM detector 4 by low-pass filter 42 and are applied to the reference voltage input end of subtraction circuit 8 through level shifter 41. As a result, the difference between DC voltage applied to circuit 8 through level shifters 7 and 41 is generated only by DC components in output signals of detector 4, and the AGC can be controlled by this difference. Then, the blind sector voltage set to circuit 8 is almost prevented from changing due to the irregularity of operations of other circuits and the fluctuation of the power supply voltage, so that the AGC circuit which has always a stable operation can be easily constituted. |
