Servo System - Samsung WA31273A Technical Manual

The data separator provides complete encoding, decoding, and synchronization for 8,9(0,4,4) GCR
data. In data read mode, this circuit performs clock recovery, code word synchronization, decoding,
sync byte detection, de-scrambling, and NRZ interface conversation.
5-2-3 Servo Demodulator
The servo demodulator captures four separate servo bursts and provides an amplified and offset
version of the voltages captured for each at the A, B, C and D output.
5-2-3 Preamplifier and Write Drive IC
The Preamplifier and Write Drive IC provides the R/W head selection, preamplifier and write driver
functions. It amplifies the low-amplitude single ended ∆I current the R/W heads generate and
transmits them to the Pulse Detector module in the Read/Write IC. It also outputs the write data
receives from the Read/Write IC.
5-3

Servo System

The Servo System controls the position of the read/write heads and holds them on track during
read/write operations. The Servo System also compensates for thermal offsets between heads on
different surfaces and vibration and shock applied to the drive.
The Winner 3A WA31273A / WA32543A / WA33203A / WA32163A / WA31083A, Winner 2A
WA32162A is an Embedded Sector Servo System Positioning information is radially located in 72
evenly-spaced servo sectors on each track.
Radial position information can be provided from these sectors for each data head, 72 times per
revolution. Because the drive used multiple data zones and each zone has a different bit density, split
data fields are necessary to optimally use the non-servo area of the disk. The servo area remains
phase-coherent across the surface of the disk, even though the disk has various data zones. The main
advantage of the Embedded Sector Servo System is that it can eliminate the problems of static and
dynamic offsets between heads on different surfaces. The Winner 3A WA31273A / WA32543A /
WA33203A / WA32163A / WA31083A, Winner 2A WA32162A Servo System is classified as a
digital servo system because the track-following control and seek control, bias cancellation, and other
typical tasks are done in SID-9501D DSP microprocessor.
The Servo system has three modes of operation, track-following mode, settle mode, velocity control
mode.
1. The track-following mode is used when heads are "on-track." this is a position loop with an
integrator in the compensation.
2. The Settle mode is used for all access; head switches, short-track seeks and long-track seeks. The
settle mode is a position loop with velocity damping. The settle mode does not use feed forward.
3. The velocity control mode is used for acceleration and deceleration of the actuator for two or
WA31273A / WA32543A / WA33203A / WA32163A / WA31083A / WA32162A5-13
Disk Drive Operation