| 摘要 |
PURPOSE:To eliminate the information for automatic gain control circuit which is included in the servo information of a magnetic disk by providing a means to detect the gain to an automatic gain control circuit. CONSTITUTION:A switcher 92 selects the fixed gain mode/automatic gain mode in which the amplitude of a read signal read from a disk by a variable gain device 90 is compared with the amplitude of a prescribed set voltage in an amplitude detector 91 and a difference signal is supplied, and a gain in the selected mode is converted to a voltage or a current is outputted from the switcher 92. This output is supplied to a control voltage generator 93 where a gain setting voltage is generated and it is supplied to a gain device 90 and a gain detector 94. In the mean time, the detector 94 detects the gain in the gain device 90 by means of equalization, and the detected output is supplied to the generator 93. Thus the gain of the gain device 90 is stably controlled based on the difference between its own gain and the set gain. As a result, the information to control the stability of an automatic gain control circuit included in a servo information of a magnetic disk is made unnecessary, hence the storage capacity of a magnetic disk device can virtually be enhanced.
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