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DISK DRIVE OPERATION
SpinPoint V40
Product Manual
34
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 MR write/read offsets and thermal offsets between heads
on different surfaces and for vibration and shock applied to the drive.
The SpinPoint V40 is an Embedded Sector Servo System. Positioning information is radially located in 192
evenly spaced servo sectors on each track.
Radial position information can be provided from these sectors for each data head, 192 times per revolution.
Because the drive incorporates multiple data zones and each zone has a different bit density, split data fields
are necessary for optimal use of 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 eliminates the problems of static and dynamic offsets between heads on
different surfaces. The SpinPoint V40 Servo System is classified as a digital servo system because track-
following and seek control, bias cancellation, and other typical tasks are done in a Digital Signal Processor
(DSP).
The Servo system has three modes of operation: track-following mode, settle mode, and velocity control
mode.
1. Track-following mode is used when heads are “on-track.” This is a position loop with an
integrator in the compensation.
2. Settle mode is used for all accesses; head switches, short-track seeks and long-track seeks.
Settle mode is a position loop with velocity damping. Settle mode does not use feed forward.
3. Velocity control mode is used for acceleration and deceleration of the actuator for a seek of two
or more tracks. A seek operation of this length is accomplished with a velocity control loop.
The drive’s ROM stores the velocity profile in a look-up table.
The feed forward compensation is used while the bandwidth of the control loop is kept low.
5.4 Read and Write Operations
The following two sections describe the read and write channels.
5.4.1 The Read Channel
The drive has one read/write head for each of the data surfaces. The signal path for the Read Channel starts
at the read/write heads. When the magnetic flux transitions recorded on a disk pass under the head, they
generate low-amplitude, differential output voltages. The read/write head transfers these signals to the
flexible circuit’s amplifier, which amplifies the signal.
The flexible circuit transmits the pre-amplified signal from the HDA to the PCBA. The EPRML channel on
the PCBA shapes, filters, detects, synchronizes, and decodes the data from the disk. The Read/Write IC then
sends the resynchronized data output to the SID2001 DSP & Interface/Disk Controller.