| 摘要 |
PURPOSE:To attain ease of system design of a read circuit by adjusting automatically the gain of an amplifier in response to the output change of a detection signal from a magnetic head. CONSTITUTION:A detection signal is outputted from the magnetic head 2 and amplified by an amplifier 4 while a floppy disc is turned. An output signal S1 of the amplifier 4 is inputted to a gain control means 14. That is, the gain control means 14 holds the peak of the output signal S1 by using a peak hold circuit 16, the signal subjected to peak hold is compared with a reference voltate 18 at a comparator 20 and when the output peak amplitude of the amplifier 4 exceeds the reference voltage, a current corresponding to both the voltages is supplied from a current source 34 to transistors (TR)32, 33 constituting a current mirror circuit. The current flowed to the TR22 is fed to a gain control input terminal 10a of the amplifier 4 as a gain control signal C1. |
