| 摘要 |
A gain control circuit particularly suitable for compressing or expanding the dynamic range of an audio signal, and thereby reducing noise produced during recording and playback comprises an input circuit receiving an input signal, first and second differential amplifiers each supplied from the input circuit with a signal derived from the input signal, with the amplifying elements of each being complementary to the amplifying elements of the other, a first pair of transistors having their emitters coupled to the output of the first differential amplifier and a second pair of transistors having their emitters coupled to the output of the second differential amplifier. The transistors of each pair are of the same conductivity type as the amplifying elements of the associated differential amplifier. The collectors of the transistors of each pair are jointed respectively to the collectors of the corresponding transistors of the other pair. Control voltage input terminals are respectively connected to one transistor of each pair and an opposite transistor of the other pair. A feedback signal is applied from the joined collectors of the one transistors to the input circuit, and an output current is applied from the joined collectors of the other transistors to an output stage which can include a load resistor or a current-to-voltage converter circuit. This arrangement prevents variation in total static current when gain is varied, thereby achieving a superior signal-to-noise characteristic.
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