| 摘要 |
PURPOSE:To make an output level stable by applying a prescribed level shift to one of two output signals of a differential gain control amplifier, comparing the level of both the signals and using a compared output so as to control the gain. CONSTITUTION:The automatic gain control circuit consists of a gain control amplifier 21, a level shift means 22, a level comparator 23, an integration filter 24 and a control signal amplifier 25. A signal supplied from an input terminal 30 is amplified by the amplifier 21 and fed to the means 22. One of the signals of opposite polarity and having equal DC level and amplitude appearing across an inductor L of the means 22 is fed as it is to the comparator 23 and the other is fed thereto while being shifted by a DELTAV with a resistor R4. The comparators 23 compares the signals and controls the amplifier 21 via the filter 24 and the amplifier 25. Thus, the amplitude level of the signal obtained at output terminals 28, 29 is fixed to 2DELTAV.
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