| 摘要 |
PURPOSE: An AGC circuit for controlling a gain of an amplifier is provided to prevent the amplification of noise by setting properly the gain of the amplifier. CONSTITUTION: An AGC circuit includes a level detector, an AGC signal generator, a constant level signal generator circuit, a switching circuit, an AGC amplifier, and a signal presence/absence judgment circuit. The level detector circuit is used for detecting a level of a playback signal. The AGC signal generator circuit(10) is used for generating an AGC signal according to the detected level. The constant level signal generator circuit is used for generating a constant level signal at a predetermined level. The switching circuit(14) is used for selecting and outputting either the AGC signal or the constant level signal as a control signal. The AGC amplifier(AP1) is used for amplifying and outputting the playback signal at a gain on the basis of the control signal. The signal presence/absence judgment circuit is used for judging a no-signal state or a signal present state by whether or not the signal level of the playback signal is equal to or less than a predetermined level. The switching circuit selects the AGC signal according to the judgment result of the signal presence/absence judgment circuit when there is a signal present or the constant level signal when there is no signal.
|
