Patent ID: 7605995

Claim:
A servo writer comprising: a direct-current erasing head configured to magnetize a servo band of a magnetic tape, wherein a direction of magnetization thereof is a first direction of lengthwise directions of the magnetic tape; a servo signal write head configured to record a servo signal on the servo band by magnetization of which a direction is a second direction opposite to the first direction; a verification head configured to retrieve the servo signal recorded on the servo band; an analog-to-digital converter configured to convert the servo signal retrieved by the verification head to a digital signal; and a signal output controller configured to regulate a recording current to be supplied to at least one of the direct-current erasing head and the servo signal write head, wherein the signal output controller comprises: a peak value detection unit configured to detect a peak value in each pulse of the digital signal output from the analog-to-digital converter, wherein the peak value comprises either of a positive-going peak value and a negative-going peak value; a low-pass filter unit configured to transmit as an input value the peak value received from the peak value detection unit, wherein the input value is allowed to follow a change in the peak value as long as a frequency calculated based upon times of detection of respective peak values is below a predetermined frequency; and an output determination unit configured to determine an output value of the recording current, based upon the input value transmitted through the low-pass filter unit.