| 摘要 |
<p>A digital automatic gain control apparatus designed to control gain in such a way that when an analog video signal is converted into digital signals for processing, the input of the A-D converter (2) is maintained at a fixed level, and after the analog signal has been converted into digital form, the output of the digital system circuit is also maintained at a fixed level. In this apparatus, an input signal is passed through an analog variable gain amplifier, the signal is converted into digital form, the output of an A-D converter is passed through a digital variable gain amplifier (3). The amplitude level of the output of the digital variable gain amplifier (3) is detected by an amplitude detecting means and is controlled so as to be equal to a specified reference value. At this time, the analog variable gain amplifier (1) is controlled so that the level of the control signal for controlling the digital variable gain amplifier (3) is equal to a specified reference value, thereby maintaining the input signal of the A-D converter (2) at a fixed level. Gain control of the analog signal system and the digital signal system, before and after the A-D converter (2) is effected by a single amplitude detecting means.</p> |
