| 摘要 |
PROBLEM TO BE SOLVED: To improve setting of an amplifier gain by amplifying a detected current containing plural DC levels different in time sequence by varying the gain in each period within a dynamic range of a current-voltage conversion amplifier. SOLUTION: This head amplifier demodulates digital information by a modulation/demodulation circuit 33 and reads each address information. An MPU 34 counts the predetermined number of clocks starting with the rear end mirror part of a PID part as a reference of timing, and then, it is switched from Low to High. After that, the MPU counts the number of clocks equivalent to a data length, and then, makes a Data/PID gate signal 3 effective by switching from High to Low. Being shifted from the data part to the PID part, the Data/PID gate signal 3 changes to High and selects specified gain resister, and being shifted from the PID part to the data part, the signal selects another gain resister. A ratio of the two gain resisters should be set approximately equal to a ratio of a mirror level to a land/groove level. |
