| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic gain control circuit that can increase an S/N ratio of an output signal whatever frequency relationship a desired signal and a disturbing signal have.SOLUTION: The automatic gain control circuit includes: a reception circuit for measuring a level of an input radio signal, separating a desired signal as a signal included in the radio signal which has a frequency to be demodulated and a disturbing signal as a signal having a higher level than the desired signal and having a frequency not to be demodulated, and comparing the frequencies; and a variable attenuation circuit having a variable degree of attenuation of the level of the radio signal input into the reception circuit and having a variable frequency characteristic of the attenuation. In response to a frequency relationship between the desired signal and the disturbing signal, the reception circuit selectively increases a low frequency side of attenuation, increases a high frequency side of attenuation or keeps the attenuation constant irrespective of the frequency in the variable attenuation circuit. |
