Fujitsu MHV2120AT User Manual download pdf (Page 66)

Theory of Device Operation

4-10 C141-E218

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 signal is

converted into the read data by the ENDEC circuit based on the read data

maximum-likelihood-detected by the Viterbi detection circuit.

(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

boost-up gain according to the transfer frequency of each zone.

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

Figure 4.5 Frequency characteristic of programmable filter

-3 dB

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 279 280

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Fujitsu MHV2120AT User Manual Page 66