FUJITSU MPF3XXXAT - Manual (Page 55)

C141-E099-01EN 4 - 10
(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.
4.6.4 Time 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.