| 摘要 |
PURPOSE:To expand even a fine signal without being affected by a noise by preliminarily supplying minute constant currents for controlling gain to a control terminal for controlling the gain of a variable gain amplifier which expands a compressed signal at the time of recording. CONSTITUTION:A current control amplifier (CCA) 5 amplifies the output signal of a differential amplifier 1 according to the output DC current of a smoothing circuit 4. A constant current source 7 supplies constant current to the CCA 5 in order to increase the gain of the CCA 5. Then, at the time of recording, the gain of the CCA 5 is preliminarily increased to decrease the gain of the differential amplifier 1, the compression of a signal is usually not operated, and a signal level is increased. Thus, the recorded signal level is higher and the output level of the reproduced signal is increased according thereto. Then, even when the noise is detected, a prescribed characteristic can be obtained as an overall characteristic, and the S/N of the expanded signal can be improved. |
