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Servo and Data Separation Using Time Domain Techniques

IP.com Disclosure Number: IPCOM000080413D
Original Publication Date: 1973-Dec-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Schwarz, TA: AUTHOR

Abstract

In servo systems utilizing dual-layer servo disks, the servo signal is contaminated by subharmonic spectral components of the data signal causing errors in the position signal. The present techniques of frequency separation and filtering can be significantly improved, by using the time domain techniques for separating the servo and data signals.

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Servo and Data Separation Using Time Domain Techniques

In servo systems utilizing dual-layer servo disks, the servo signal is contaminated by subharmonic spectral components of the data signal causing errors in the position signal. The present techniques of frequency separation and filtering can be significantly improved, by using the time domain techniques for separating the servo and data signals.

Referring to Fig. 1, the servo information represented by servo pulses are dispersed in the time domain by a transverse filter 1, whose transfer function is h(t). The output of the transversal filter 1 is recorded by recording and readback channel 2 onto a magnetic disk, causing the time dispersion output of the transverse filter 1 to become a spatial dispersion on the disk. When the signal is read back by channel 2, it is recompressed into pulses by an inverse-time match compression filter 3 whose transfer function is h(-t). The output of the compression filter 3 is a pulse which is the convolution of the dispersed signal with its time-inverse. The dispersion code for the compression filter 3 is so selected that its autocorrelation function is a narrow pulse with small side lobes.

Fig. 2 shows in greater detail the dispersion compression system for recording and recovering the servo information. The servo information is fed into a tapped delay line 4. The tapped delay line 4 has sealing amplifiers 5 which multiply the output of each tap by either a +1 or -1 output. The placement of the taps on the delay line 4 and the amplifiers' 5 gain value of each tap represents a coding polynomial. The output of each of the amplifiers are summed by summing amplifier 6 to produce an instantaneous output which is recorded by the recording channel 7.

When the information is read back by the recording channel 7, the signal received is fed into a similar tapped delay line 9 having taps at the same location as tapped delay line 4. Again each tap has a sealing amplifier 8 for...