Method to write servo on multi-channels with voltage mode...

Details Method to write servo on multi-channels with voltage mode... Method to write servo on multi-channels with voltage mode...

2001-10-29

2004-05-11

Faber, Alan T (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

C360S068000, C360S063000

Reexamination Certificate

active

06735030

ABSTRACT:

FIELD OF THE INVENTION
The present invention is generally related to the field of mass media information storage devices, and more particularly to circuits for controlling the write current used to drive a thin film write head.
BACKGROUND OF THE INVENTION
Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus.
FIG. 1
shows an example of a prior art disk drive mass storage system
10
. Disk drive system
10
interfaces with and exchanges data with a host
32
during read and write operations. Disk drive system
10
includes a number of rotating platters
12
mounted on a base
14
. The platters
12
are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter
12
coupleable to a head
16
which transfers data to and from a preamplifier
26
. The preamp
26
is coupled to a synchronously sampled data (SSD) channel
28
comprising a read channel and a write channel, and a control circuit
30
. SSD channel
28
and control circuit
30
are used to process data being read from and written to platters
12
, and to control the various operations of disk drive mass storage system
10
. Host
32
exchanges digital data with control circuit
30
.
Data is stored and retrieved from each side of the magnetic platters
12
by heads
18
,
20
which comprise a read head
18
and a write head
20
at the tip thereof. The conventional readhead
18
and writehead
20
comprise magneto-resistive heads adapted to read or write data from/to platters
12
when current is passed through them. Heads
18
,
20
are coupled to preamplifier
26
that serves as an interface between read/write heads
18
/
20
of disk/head assembly
10
and SSD channel
28
. The preamp
26
provides amplification to the waveform data signals as needed. A preamp
26
may comprise a single chip containing a reader amplifier
22
, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp
26
may comprise separate components rather than residing on a single chip.
It is desired to achieve high data rates of greater than 1 Gb/s in the write mode. Conventional solutions use a voltage mode to deliver the write data to an H-current switch in the pre-amplifier
26
. This voltage mode, however, is not adequate for high data rates greater than 1 Gb/s since the on-chip interconnection and the loading of inactive channels slows the write data. Conversely, if the current mode is utilized, the current mode typically requires two signal lines to achieve a differential current mode for each channel. Typically, the pre-amplifier
26
can have 1, 2, 4, 8, 10 or 12 channels. Thus, in a servo multi-channel write operation, for a 12-channel pre-amplifier, 24 signal buses would need to be laid out all over the integrated circuit, which disadvantagly increases the die size and increases the layout routing complexity.
Hence, the conventional limitations in write data circuits are that the voltage mode is not fast enough, and in the current mode conventional circuits become complex. In addition, parasitic loading effects of on-chip interconnection on data speeds limits the write data rate. In addition, the capacitance loading effect of inactive channels on the write data signals also limits the use of writing using the current mode.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a write data circuit selectively utilizing current mode ECL level data when writing to a signal channel, and selectively utilizing a voltage mode ECL level when writing to multiple channels. Advantageously, in a single channel write event, the current mode delivers very fast and sharp write currents to the preamplifier H-switch without performance degradation due to on-chip interconnection. When writing to multiple channels, such as in the servo mode, the servo multi-channel write operation does not need to be very fast, and thus the voltage mode write data is adequate. In addition, both the voltage mode and current mode write data share the same differential interconnection to the heads, which advantageously reduces the die area and provides minimum production cost and reduces complexity. For instance, two lines are utilized for four channels, instead of eight lines.


REFERENCES:
patent: 6271977 (2001-08-01), Chung
patent: 6324028 (2001-11-01), Ramalho

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