Fujitsu MPF3XXXAT manual Time base generator circuit

(2)Programmable filter

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 each DAC circuit in read channel. The MPU optimizes the cut-off frequency and boost-up gain according to the transfer frequency of each zone.

(3)FIR (Digital Finite Impulse Response Equalization Filter) adaptation circuit

The FIR provides support for changing equalization needs from head to head and zone to zone. The FIR is a specialized digital filter with ten independently controlled coefficients.

(4)Viterbi detection circuit

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

(5)Data separator circuit

The data separator circuit generates clocks in synchronization with the output of the adaptive equalizer circuit. To write data, the VFO circuit generates clocks in synchronization with the clock signals from a synthesizer.

(6)48/51 GCR decoder

This circuit converts the 51-bits read data into the 48-bits NRZ data.

4.6.4Time base generator 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 15 zones to set the data transfer rate. Table 4.2 describes the data transfer rate and recording density (BPI) of each zone.

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