CHAPTER 4 Theory of Device Operation. Fujitsu MHT2040AT, MHT2030AT, MHT2080AT, MHT2020AT, MHT2060AT

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CHAPTER 4 Theory of Device Operation. Fujitsu MHT2040AT, MHT2030AT, MHT2080AT, MHT2020AT, MHT2060AT | Manualzz

CHAPTER 4 Theory of Device Operation










Circuit Configuration

Power-on Sequence


Read/write Circuit

Servo Control

This chapter explains basic design concepts of the disk drive. Also, this chapter explains subassemblies of the disk drive, each sequence, servo control, and electrical circuit blocks.

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Theory of Device Operation

4.1 Outline

This chapter consists of two parts. First part (Section 4.2) explains mechanical assemblies of the disk drive. Second part (Sections 4.3 through 4.7) explains a servo information recorded in the disk drive and drive control method.

4.2 Subassemblies

The disk drive consists of a disk enclosure (DE) and printed circuit assembly


The DE contains all movable parts in the disk drive, including the disk, spindle, actuator, read/write head, and air filter. For details, see Subsections 4.2.1 to 4.2.4.

The PCA contains the control circuits for the disk drive. The disk drive has one

PCA. For details, see Sections 4.3.

4.2.1 Disk

The DE contains disks with an outer diameter of 65 mm and an inner diameter of

20 mm.

Servo data is recorded on each cylinder (total 150). Servo data written at factory is read out by the read head. For servo data, see Section 4.7.

4.2.2 Spindle

The spindle consists of a disk stack assembly and spindle motor. The disk stack assembly is activated by the direct drive sensor-less DC spindle motor, which has a speed of 4,200 rpm


1%. The spindle is controlled with detecting a PHASE signal generated by counter electromotive voltage of the spindle motor at starting.

4.2.3 Actuator

The actuator consists of a voice coil motor (VCM) and a head carriage. The

VCM moves the head carriage along the inner or outer edge of the disk. The head carriage position is controlled by feeding back the difference of the target position that is detected and reproduced from the servo information read by the read/write head.

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4.3 Circuit Configuration

4.2.4 Air filter

There are two types of air filters: a breather filter and a circulation filter.

The breather filter makes an air in and out of the DE to prevent unnecessary pressure around the spindle when the disk starts or stops rotating. When disk drives are transported under conditions where the air pressure changes a lot, filtered air is circulated in the DE.

The circulation filter cleans out dust and dirt from inside the DE. The disk drive cycles air continuously through the circulation filter through an enclosed loop air cycle system operated by a blower on the rotating disk.

4.3 Circuit Configuration

Figure 4.1 shows the power supply configuration of the disk drive, and Figure 4.2

shows the disk drive circuit configuration.

(1) Read/write circuit

The read/write circuit consists of two circuits; read/write preamplifier (PreAMP) and read channel (RDC).

The PreAMP consists of the write current switch circuit, that flows the write current to the head coil, and the voltage amplifier circuit, that amplitudes the read output from the head.

The RDC is the read demodulation circuit using the Modified Extended Partial

Response (MEEPR), and contains the Viterbi detector, programmable filter, adaptable transversal filter, times base generator, data separator circuits, 32/34

RLL (Limited) encoder Run Length and servo demodulation circuit.

(2) Servo circuit

The position and speed of the voice coil motor are controlled by 2 closed-loop servo using the servo information recorded on the data surface. The servo information is an analog signal converted to digital for processing by a MPU and then reconverted to an analog signal for control of the voice coil motor.

The MPU precisely sets each head on the track according on the servo information on the media surface.

(3) Spindle motor driver circuit

The circuit measures the interval of a PHASE signal generated by counterelectromotive voltage of a motor and controls the motor speed comparing target speed.

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Theory of Device Operation

(4) Controller circuit

Major functions are listed below.

Data buffer management

ATA interface control and data transfer control

Sector format control

Defect management

ECC control

Error recovery and self-diagnosis

Figure 4.1 Power Supply Configuration

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Data Buffer


4.3 Circuit Configuration

ATA Interface



Anchor (88i553x; Marvell)



Flash ROM









SP Motor VCM Thermistor


R/W Pre-Amp




Figure 4.2 Circuit Configuration

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Theory of Device Operation

4.4 Power-on Sequence

Figure 4.3 describes the operation sequence of the disk drive at power-on. The outline is described below.

a) After the power is turned on, the disk drive executes the MPU bus test, internal register read/write test, and work RAM read/write test. When the self-diagnosis terminates successfully, the disk drive starts the spindle motor.

b) The disk drive executes self-diagnosis (data buffer read/write test) after enabling response to the ATA bus.

c) After confirming that the spindle motor has reached rated speed, the head assembly is loaded on the disk.

d) The disk drive positions the heads onto the SA area and reads out the system information.

e) The disk drive sets up a requirement for execution of self-seek-calibration.

This collects data for VCM torque and mechanical external forces applied to the actuator, and updates the calibrating value.

f) The drive becomes ready. The host can issue commands.

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4.5 Self-calibration


Start a)

Self-diagnosis 1

- MPU bus test

- Internal register

write/read test

- Work RAM write/read


The spindle motor starts.


Self-diagnosis 2

- Data buffer write/read

test c)

Confirming spindle motor speed

Load the head assembly d)

Initial on-track and read out of system information e)

Execute self-calibration f)

Drive ready state

(command waiting state)


Figure 4.3 Power-on operation sequence

4.5 Self-calibration

The disk drive occasionally performs self-calibration in order to sense and calibrate mechanical external forces on the actuator, and VCM torque. This enables precise seek and read/write operations.

4.5.1 Self-calibration contents

(1) Sensing and compensating for external forces

The actuator suffers from torque due to the FPC forces and winds accompanying disk revolution. The torque vary with the disk drive and the cylinder where the head is positioned. To execute stable fast seek operations, external forces are occasionally sensed.

The firmware of the drive measures and stores the force (value of the actuator motor drive current) that balances the torque for stopping head stably. This includes the current offset in the power amplifier circuit and DAC system.

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Theory of Device Operation

The forces are compensated by adding the measured value to the specified current value to the power amplifier. This makes the stable servo control.

To compensate torque varying by the cylinder, the disk is divided into 16 areas from the innermost to the outermost circumference and the compensating value is measured at the measuring cylinder on each area at factory calibration. The measured values are stored in the SA cylinder. In the self-calibration, the compensating value is updated using the value in the SA cylinder.

(2) Compensating open loop gain

Torque constant value of the VCM has a dispersion for each drive, and varies depending on the cylinder that the head is positioned. To realize the high speed seek operation, the value that compensates torque constant value change and loop gain change of the whole servo system due to temperature change is measured and stored.

For sensing, the firmware mixes the disturbance signal to the position signal at the state that the head is positioned to any cylinder. The firmware calculates the loop gain from the position signal and stores the compensation value against to the target gain as ratio.

For compensating, the direction current value to the power amplifier is multiplied by the compensation value. By this compensation, loop gain becomes constant value and the stable servo control is realized.

To compensate torque constant value change depending on cylinder, whole cylinders from most inner to most outer cylinder are divided into 14 partitions at calibration in the factory, and the compensation data is measured for representative cylinder of each partition. This measured value is stored in the SA area. The compensation value at self-calibration is calculated using the value in the SA area.

4.5.2 Execution timing of self-calibration

Self-calibration is performed once when power is turned on. After that, the disk drive does not perform self-calibration until it detects an error.

That is, self-calibration is performed each time one of the following events occur:

When it passes from the power on for ten seconds and the disk drive shifts to

Active Idle mode.

The number of retries to write or seek data reaches the specified value.

The error rate of data reading, writing, or seeking becomes lower than the specified value.

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4.6 Read/write Circuit

4.5.3 Command processing during self-calibration

This enables the host to execute the command without waiting for a long time, even when the disk drive is performing self-calibration. The command execution wait time is about maximum 72 ms.

When the error rate of data reading, writing, or seeking becomes lower than the specified value, self-calibration is performed to maintain disk drive stability.

If the disk drive receives a command execution request from the host while performing self-calibration, it stops the self-calibration and starts to execute the command. In other words, if a disk read or write service is necessary, the disk drive positions the head to the track requested by the host, reads or writes data, and then restarts calibration after 10 seconds.

If the error rate recovers to a value exceeding the specified value, self-calibration is not performed.

4.6 Read/write Circuit

The read/write circuit consists of the read/write preamplifier (PreAMP), the write circuit, the read circuit, and the time base generator in the read channel (RDC).

Figure 4.4 is a block diagram of the read/write circuit.

4.6.1 Read/write preamplifier (PreAMP)

PreAMP equips a read preamplifier and a write current switch, that sets the bias current to the MR device and the current in writing. Each channel is connected to each data head, and PreAMP switches channel by serial I/O. In the event of any abnormalities, including a head short-circuit or head open circuit, the write unsafe signal is generated so that abnormal write does not occur.

4.6.2 Write circuit

The write data is output from the hard disk controller (HDC) with the NRZ data format, and sent to the encoder circuit in the RDC. The NRZ write data is converted from 32-bit data to 34-bit data by the encoder circuit then sent to the

HDIC, and the data is written onto the media.

(1) 32/34 RLL MEEPRML

This device converts data using the 32/34 RLL (Run Length Limited) algorithm.

(2) Write precompensation

Write precompensation compensates, during a write process, for write nonlinearity generated at reading.

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Theory of Device Operation

Figure 4.4 Read/write circuit block diagram

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4.6 Read/write Circuit

4.6.3 Read circuit

The head read signal from the PreAMP is regulated by the automatic gain control

(AGC) circuit. Then the output is converted into the sampled read data pulse by the programmable filter circuit and the flash digitizer circuit. This clock signal is converted into the NRZ data by the ENDEC circuit based on the read data maximum-likelihood-detected by the Viterbi detection circuit, then is sent to the


(1) AGC circuit

The AGC circuit automatically regulates the output amplitude to a constant value even when the input amplitude level fluctuates. The AGC amplifier output is maintained at a constant level even when the head output fluctuates due to the head characteristics or outer/inner head positions.

(2) Programmable filter circuit

The programmable filter circuit has a low-pass filter function that eliminates unnecessary high frequency noise component and a high frequency boost-up function that equalizes the waveform of the read signal.

Cut-off frequency of the low-pass filter and boost-up gain are controlled from the register in read channel by an instruction of the serial data signal from MPU

(M5). The MPU optimizes the cut-off frequency and boost-up gain according to the transfer frequency of each zone.

Figure 4.5 shows the frequency characteristic sample of the programmable filter.

-3 dB

Figure 4.5 Frequency characteristic of programmable filter

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Theory of Device Operation

(3) FIR circuit

This circuit is 10-tap sampled analog transversal filter circuit that equalizes the head read signal to the Modified Extended Partial Response (MEEPR) waveform.

(4) A/D converter circuit

This circuit changes Sampled Read Data Pulse from the FIR circuit into Digital

Read Data.

(5) Viterbi detection circuit

The sample hold waveform output from the flash digitizer circuit is sent to the

Viterbi detection circuit. The Viterbi detection circuit demodulates data according to the survivor path sequence.


This circuit converts the 34-bit read data into the 32-bit NRZ data.

4.6.4 Digital PLL circuit

The drive uses constant density recording to increase total capacity. This is different from the conventional method of recording data with a fixed data transfer rate at all data area. In the constant density recording method, data area is divided into zones by radius and the data transfer rate is set so that the recording density of the inner cylinder of each zone is nearly constant. The drive divides data area into 30 zones to set the data transfer rate.

The MPU transfers the data transfer rate setup data (SD/SC) to the RDC that includes the Digital PLL circuit to change the data transfer rate.

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4.7 Servo Control

4.7 Servo Control

The actuator motor and the spindle motor are submitted to servo control. The actuator motor is controlled for moving and positioning the head to the track containing the desired data. To turn the disk at a constant velocity, the actuator motor is controlled according to the servo data that is written on the data side beforehand.

4.7.1 Servo control circuit

Figure 4.6 is the block diagram of the servo control circuit. The following describes the functions of the blocks:





Servo burst capture

Position Sense

MPU core








VCM current



CSR: Current Sense Resister

VCM: Voice Coil Motor


Spindle motor control



Spindle motor

Figure 4.6 Block diagram of servo control circuit

(1) Microprocessor unit (MPU)

The MPU executes startup of the spindle motor, movement to the reference cylinder, seek to the specified cylinder, and calibration operations. Main internal operation of the MPU are shown below.

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Theory of Device Operation

The major internal operations are listed below.


Spindle motor start

Starts the spindle motor and accelerates it to normal speed when power is applied.


Move head to reference cylinder

Drives the VCM to position the head at the any cylinder in the data area. The logical initial cylinder is at the outermost circumference (cylinder 0).


Seek to specified cylinder

Drives the VCM to position the head to the specified cylinder.



Senses and stores the thermal offset between heads and the mechanical forces on the actuator, and stores the calibration value.

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4.7 Servo Control

(2) Servo burst capture circuit

The servo burst capture circuit reproduces signals (position signals) that indicate the head position from the servo data on the data surface. From the servo area on the data area surface, via the data head, the burst signal of SERVO A, SERVO B,

SERVO C, and SERVO D is output as shown in Figure 4.9 in subsequent to the servo mark, gray code that indicates the cylinder position, and index information.

The servo signals do A/D-convert by Fourier-demodulator in the servo burst capture circuit. At that time the AGC circuit is in hold mode. The A/D converted data is recognized by the MPU as position information with A-B and C-D processed.

(3) D/A converter (DAC)

The control program calculates the specified data value (digital value) of the

VCM drive current, and the value is converted from digital-to-analog so that an analog output voltage is sent to the power amplifier.

(4) Power amplifier

The power amplifier feeds currents, corresponding to the DAC output signal voltage to the VCM.

(5) Spindle motor control circuit

The spindle motor control circuit controls the sensor-less spindle motor. A spindle driver IC with a built-in PLL(FLL) circuit that is on a hardware unit controls the sensor-less spindle motor.

(6) Driver circuit

The driver circuit is a power amplitude circuit that receives signals from the spindle motor control circuit and feeds currents to the spindle motor.

(7) VCM current sense resistor (CSR)

This resistor controls current at the power amplifier by converting the VCM current into voltage and feeding back.

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Theory of Device Operation

4.7.2 Data-surface servo format

Figure 4.7 describes the physical layout of the servo frame. The three areas indicated by (1) to (3) in Figure 4.7 are described below.

(1) Inner guard band

This area is located inside the user area, and the rotational speed of the VCM can be controlled on this cylinder area for head moving.

(2) Data area

This area is used as the user data area SA area.

(3) Outer guard band

This area is located at outer position of the user data area, and the rotational speed of the spindle can be controlled on this cylinder area for head moving.

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4.7 Servo Control

Servo frame

(150 servo frames per revolution)


Data area expand


CYLn + 1

CYLn CYLn – 1 (n: even number)

W/R Recovery

Servo Mark

Gray Code

W/R Recovery

Servo Mark

Gray Code

W/R Recovery

Servo Mark

Gray Code

Erase Servo A

Servo B

Servo C




Servo D



Servo B

Servo A


Servo C









Erase: DC erase area

Figure 4.7 Physical sector servo configuration on disk surface

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Theory of Device Operation

4.7.3 Servo frame format

As the servo information, the IDD uses the two-phase servo generated from the gray code and servo A to D. This servo information is used for positioning operation of radius direction and position detection of circumstance direction.

The servo frame consists of 6 blocks; write/read recovery, servo mark, gray code, servo A to D, and PAD. Figure 4.8 shows the servo frame format.

Figure 4.8 Servo frame format

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4.7 Servo Control

(1) Write/read recovery

This area is used to absorb the write/read transient and to stabilize the AGC.

(2) Servo mark

This area generates a timing for demodulating the gray code and positiondemodulating the servo A to D by detecting the servo mark.

(3) Gray code (including sector address bits)

This area is used as cylinder address. The data in this area is converted into the binary data by the gray code demodulation circuit

(4) Servo A, servo B, servo C, servo D

This area is used as position signals between tracks and the IDD control at ontrack so that servo A level equals to servo B level.

(5) PAD

This area is used as a gap between servo and data.

4.7.4 Actuator motor control

The voice coil motor (VCM) is controlled by feeding back the servo data recorded on the data surface. The MPU fetches the position sense data on the servo frame at a constant interval of sampling time, executes calculation, and updates the

VCM drive current.

The servo control of the actuator includes the operation to move the head to the reference cylinder, the seek operation to move the head to the target cylinder to read or write data, and the track-following operation to position the head onto the target track.

(1) Operation to move the head to the reference cylinder

The MPU moves the head to the reference cylinder when the power is turned.

The reference cylinder is in the data area.

When power is applied the heads are moved from the outside of media to the normal servo data zone in the following sequence: a) Micro current is fed to the VCM to press the head against the outer direction.

b) The head is loaded on the disk.

c) When the servo mark is detected the head is moved slowly toward the inner circumference at a constant speed.

d) If the head is stopped at the reference cylinder from there. Track following control starts.

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Theory of Device Operation

(2) Seek operation

Upon a data read/write request from the host, the MPU confirms the necessity of access to the disk. If a read/write instruction is issued, the MPU seeks the desired track.

The MPU feeds the VCM current via the D/A converter and power amplifier to move the head. The MPU calculates the difference (speed error) between the specified target position and the current position for each sampling timing during head moving. The MPU then feeds the VCM drive current by setting the calculated result into the D/A converter. The calculation is digitally executed by the firmware. When the head arrives at the target cylinder, the track is followed.

(3) Track following operation

Except during head movement to the reference cylinder and seek operation under the spindle rotates in steady speed, the MPU does track following control. To position the head at the center of a track, the DSP drives the VCM by feeding micro current. For each sampling time, the VCM drive current is determined by filtering the position difference between the target position and the position clarified by the detected position sense data. The filtering includes servo compensation. These are digitally controlled by the firmware.

4.7.5 Spindle motor control

Hall-less three-phase twelve-pole motor is used for the spindle motor, and the 3phase full/half-wave analog current control circuit is used as the spindle motor driver (called SVC hereafter). The firmware operates on the MPU manufactured by Fujitsu. The spindle motor is controlled by sending several signals from the

MPU to the SVC. There are three modes for the spindle control; start mode, acceleration mode, and stable rotation mode.

(1) Start mode

When power is supplied, the spindle motor is started in the following sequence: a) After the power is turned on, the MPU sends a signal to the SVC to charge the charge pump capacitor of the SVC. The charged amount defines the current that flows in the spindle motor.

b) When the charge pump capacitor is charged enough, the MPU sets the SVC to the motor start mode. Then, a current (approx. 0.3 A) flows into the spindle motor.

c) A phase switching signal is generated and the phase of the current flowed in the motor is changed in the order of (V-phase to U-phase), (W-phase to Uphase), (W-phase to V-phase), (U-phase to V-phase), (U-phase to W-phase), and (V-phase to W-phase) (after that, repeating this order).

d) During phase switching, the spindle motor starts rotating in low speed, and generates a counter electromotive force. The SVC detects this counter electromotive force and reports to the MPU using a PHASE signal for speed detection.

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4.7 Servo Control

e) The MPU is waiting for a PHASE signal. When no phase signal is sent for a specific period, the MPU resets the SVC and starts from the beginning.

When a PHASE signal is sent, the SVC enters the acceleration mode.

(2) Acceleration mode

In this mode, the MPU stops to send the phase switching signal to the SVC. The

SVC starts a phase switching by itself based on the counter electromotive force.

Then, rotation of the spindle motor accelerates. The MPU calculates a rotational speed of the spindle motor based on the PHASE signal from the SVC, and waits till the rotational speed reaches 4,200 rpm. When the rotational speed reaches

4,200 rpm, the SVC enters the stable rotation mode.

(3) Stable rotation mode

The SVC calculates a time for one revolution of the spindle motor based on the

PHASE signal. The MPU takes a difference between the current time and a time for one revolution at 4,200 rpm that the MPU already recognized. Then, the MPU keeps the rotational speed to 4,200 rpm by charging or discharging the charge pump for the different time. For example, when the actual rotational speed is

4,000 rpm, the time for one revolution is 15.000 ms. And the time for one revolution at 4,200 rpm is 14.286 ms. Therefore, the MPU charges the charge pump for 0.714 ms


k (k: constant value). This makes the flowed current into the motor higher and the rotational speed up. When the actual rotational speed is faster than 4,200 rpm, the MPU discharges the pump the other way. This control

(charging/discharging) is performed every 1 revolution.

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Key Features

  • 80 GB 2.5" 4200 RPM Ultra-ATA/100
  • HDD
  • Storage drive buffer size: 8 MB
  • 99 g

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Frequently Answers and Questions

What is the capacity of the Fujitsu MHT2020AT?
The Fujitsu MHT2020AT has a capacity of 20GB.
What is the rotational speed of the Fujitsu MHT2020AT?
The Fujitsu MHT2020AT has a rotational speed of 5400RPM.
What interface does the Fujitsu MHT2020AT use?
The Fujitsu MHT2020AT uses the ATA interface.
Is the Fujitsu MHT2020AT shock-resistant?
Yes, the Fujitsu MHT2020AT is shock-resistant.
What is the form factor of the Fujitsu MHT2020AT?
The Fujitsu MHT2020AT has a 2.5-inch form factor.


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