AUTOMATIC LEVEL CONTROL CIRCUIT, AUDIO DIGITAL-SIGNAL PROCESSOR USING THE SAME, AND GAIN CONTROL METHOD OF VARIABLE GAIN AMPLIFIER

摘要

PROBLEM TO BE SOLVED: To provide an ALC (automatic level control) circuit capable of performing a flexible volume control.;SOLUTION: A variable gain amplifier 10 amplifies an input audio signal VI. A first controller 12 monitors the level in the input audio signal VI and fixes the gain α of the variable gain amplifier 10 to a predetermined value α1, when it is lower than a predetermined minimal threshold value VImin. A second controller 14 monitors the level in the output signal VO of the variable gain amplifier 10, reduces the gain α of the variable gain amplifier 10, when a predetermined maximal threshold VOmax is reduced, and increases the gain α of the amplifier 10, when the maximal threshold VOmax is lowered. The first controller 12 disables gain control of the variable gain amplifier 10 by the second controller 14, when the level in the input audio signal VI is lower than the minimal threshold VImin. A sub-amplifier 16 amplifies the input audio signal VI by gain K. An output synthesizer 18 synthesizes the output signal of the variable gain amplifier 10 and that of the sub-amplifier 16.;COPYRIGHT: (C)2010,JPO&INPIT