| 摘要 |
PURPOSE:To make the amplitude of an output signal stable even if a sudden change is inflicted to an envelope of an input signal (read signal) by changing at least one of a charging time constant and a discharge time constant in response to an external signal so as to reduce the pull-in time of the read signal. CONSTITUTION:In the pull-in operation at the start of read (time T), an FET15 is turned off, the charging time constant is brought into a small value decided by a resistor 9 and a capacitor 10 so as to quicken the trancking to a level of the read signals c1, c2. As a result, the amplitude is clipped (saturated) in VCA output signals d1, d2 because the gain of a VCA7 is very fast at first but the amplitude is pulled in fast to a prescribed amplitude in response to the small charging time constant. After a prescribed time T from the start of read operation, the charge/discharge time constants are set larger by turning on the FET15. As a result the dip in the amplitude observed after the trailing edge of a projection of the envelope is decreased by the output signals d1, d2 of the VCA7. |
