Dedicated Servo Pattern and Low-Cost Demodulator
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
An improved servo pattern and demodulator are provided for a disk storage drive. In this instance, the servo head picks up signals of two frequencies, 2.5 MHz and 1.25 MHz, whereby the ratio is two to one. The servo pattern is written whereby the phase of one frequency varies oppositely to the phase of the other frequency as the servo head moves radially over the disk. By dividing the 2.5 MHz signal by two and (Image Omitted) comparing the phase of the resulting 1.25 MHz signal to the 1.25 MHz signal of the second frequency, a position signal is obtained where the radial position is proportional to the phase difference of the two 1.25 MHz signals. The servo pattern of Fig. 1 could be used but is not practical because of clock head jitter when the pattern is written.