Servo Format; Figure 8.4 Block Diagram Of Servo Control Circuit - Fujitsu MAN3367FC - Enterprise 36.7 GB Hard Drive Product/Maintenance Manual

Principle of Operation
Data Read
Head
Head Channel
IC
bus8
HDC
Notes: DSP controls actuator servo system
MCU controls spindle servo system
(1) Processor-ASIC (Processor-application specific IC)
A DSP controls the spindle motor and the voice coil motor. The HDC sends an instruction to the
DSP through the MCU via drive interface. The Processor is a 1-chip ASIC, and also contains an
analog-to-digital converter, a digital-to-analog converter, RAM, and other logic circuits.
(2) Servo demodulator
As explained in 8.7.2, servo signals consist of a training segment, a Servo Mark segment, a Position
segment and a Gray Code segment, and 120 frames are arranged around the circumference. In the
servo demodulator, the Gray Code and Position signals from the servo signal are demodulated and
used to control head positioning.
(3) SPM/VCM driver
The SPM driver consists of a controller and a power MOSFET driver. The controller controls the
sensor-less spindle motor by checking counter electro-motive voltage, and the driver drives the
spindle motor.
The VCM driver also consists of a controller and a power MOSFET driver. The controller converts
the power amp driver signal output by the digital signal processor (DSP) into a current for driving the
VCM, and the driver drives the VCM.
The 1-chip SPM/VCM Combo driver contains power MOSFET for VCM drive.
8.7.2

Servo format

(1) Zone format
The voice coil motor is controlled to position a data head over a target cylinder, using the servo data
that has already been recorded on the data surface. Figure 8.5 shows zone format.
8-10
Processor
bus16
Servo
Demodulator
bus16
Figure 8.4 Block diagram of servo control circuit
Control
Signal
(PWM)
bus16
Drive
DSP
I/F LSI
bus16
MCU
ARM7
VCM
SPM/VCM
Combo
SPM
C141-E133-02EN