Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1999-03-15
2001-10-23
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S068000, C327S110000
Reexamination Certificate
active
06307695
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to devices which record information on a magnetic medium. More particularly, the invention concerns an improvement which increases the data rate of such devices.
2. Description of the Prior Art
Magnetic recording devices are used to write information to a magnetic medium either in analog or digital form. The magnetic medium is typically a tape, such as used in the well-known compact cassette, or known high density drives for computers which are used for backup purposes. Another common form is a disk, such as a floppy disk or a hard disk for storing programs and data in a computer.
The write channel for a magnetic recording device includes a thin film inductive head (referred to herein as “within film head”, “TFH”, or simply “inductive head”) in close proximity with the magnetic medium. A write amplifier drives a current through the head to generate a flux which very locally alters the orientation of the magnetic material, thereby writing information on the magnetic medium. The write amplifier is coupled to circuitry which receives the information to be recorded and processes the information in a form suitable for the write amplifier and according to a selected data format.
When information is written in digital form, such as for computer data storage or digital recording of music, a current is driven through the inductive head in one direction to write a binary “0” and in the opposite direction to write a “1”. When the medium is read by a suitable head, such as a magneto-resistive head, the portions recorded with a binary “0” will induce a current in the head in the one direction and portions recorded with a binary “1” will induce a current in the opposite direction, which is then decoded.
The continuing goal of those in the art is to increase the recording densities and speed (data rate) of recording to a magnetic medium. Improving the recording density allows more information to be written in a given space of the medium. Improving the recording speed is important for allowing the huge amounts of information required by today's multimedia applications to be recorded in time periods acceptable to the user. Data rates on the order of 500-600 Mb/s are proposed for near term hard disk drives for computers.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a method and apparatus which will facilitate faster recording speeds in magnetic recording devices.
Generally speaking, according to one aspect of the invention, a device for writing information to a magnetic medium includes an inductive head and a write amplifier coupled to the inductive head. The write amplifier receives an information signal, and amplifies the signal to provide a current through the inductive head to generate a flux at the inductive head for writing a bit of the information on the magnetic medium. The current for each bit of information is characterized by a rising portion, a peak portion, and a settling portion. A damping network is coupled to the inductive head, the damping network coupling a low impedance path to the head and the write amplifier, after the current reaches the peak portion, to divert current from the head thereby reducing a duration of the settling portion of the current.
The invention is based on the recognition that in order for data to be written at higher data rates, the current waveform in the inductive head must have faster rise/fall times. This is typically achieved by creating large overshoots of the write current. The invention is based on the further recognition that such large overshoots create longer settling times, which adversely affect the data rate. Large settling times create Inter Symbol Interference (ISI) in the data written to the magnetic medium, as the transition to the next bit of information occurs before the write current from the previous transition has completely settled. By coupling a low impedance discharge path to the head, the settling time is shortened as current is diverted from the head. Moreover, since the low impedance path is not coupled to the head until the peak portion of the current waveform is reached, the fast rise/fall time of the current created by a large current overshoot is not adversely affected. Thus, the invention shortens the settling time, while allowing very fast rise/fall times, thereby permitting high data rates during recording.
According to one aspect of the invention, the damping network senses a transition from the peak portion to the settling portion of the current. The damping network senses this transition by differentiating a voltage signal across the head.
According to another aspect of the invention, the inductive head includes first and second terminals and the damping network includes a high impedance branch coupled to the first terminal, and a low impedance branch coupled to the second terminal, the low impedance branch having a substantially lower impedance than the high impedance branch. A switch, coupled to the low impedance branch, is controlled by the damping network to divert the current through the low impedance branch.
In a favorable embodiment, the high impedance branch includes an RC network for differentiating the voltage across the head. The RC network thereby senses the transition of the current from the peak portion to the settling portion, and activates the switch coupling the low impedance branch. Besides employing a minimum number of components, the use of a high impedance RC network for sensing allows detection of the peak in the current, via the voltage waveform, substantially without affecting the current in the head as driven by the write amplifier.
In a practical embodiment, the device includes a second such damping network coupled in mirror arrangement with the first, so that the peak of the current is detected and damped for current in both directions of the head.
In a favorable embodiment, the damping network is programmable to allow optimal tuning in dependence on the particular head and to allow for chip-to-chip variations. The damping network may be programmed via a serial interface, for example.
The invention also relates to a method of writing to a magnetic medium, as well as to an integrated circuit which includes a write amplifier and a damping network.
REFERENCES:
patent: 5434717 (1995-07-01), Yoshinaga et al.
patent: 5668676 (1997-09-01), Voorman et al.
patent: 5726821 (1998-03-01), Cloke et al.
Goodman Edward W.
Neal Regina Y.
Philips Electronics North America Corporation
Sniezek Andrew L.
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