Fujitsu MHA2032AT, MHA2021AT manual Servo Control

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. SERVO A, SERVO B, SERVO C and SERVO D burst signals shown in Figure 4.8 followed the servo mark, cylinder gray and index information are output from the servo area on the data surface via the data head. The servo signals A/D-converts the amplitudes of the POSA, POSB, POSC and POSD signals at the peak hold circuit in the servo burst capture circuit at the timing of the STROB signal. At that time the AGC circuit is in hold mode. The difference between A/D-converted data is obtained in the MPU recognizes it as the position information.

(3) A/D converter (ADC)

The A/D converter (ADC) receives the peak-held servo signals, converts them to digital, and transfers the digital signal to the DSP unit.

(4) D/A converter (DAC)

The D/A converter (DAC) converts the VCM drive current value (digital value) calculated by the DSP unit into analog values and transfers them to the power amplifier.

(5) Power amplifier

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

(6) Spindle motor control circuit

The spindle motor control circuit controls the sensor-less spindle motor. This circuit detects number of revolution of the motor by the interrupt generated periodically, compares with the target revolution speed, then flows the current into the motor coil according to the differentation (abberration).

(7) 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.

(8) VCM current sense resistor (CSR)

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

C141-E042-01EN 4-17