Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of the amplifier
Reexamination Certificate
1999-09-28
2002-07-23
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of the amplifier
C360S065000, C360S046000, C327S551000
Reexamination Certificate
active
06424480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to devices which read information from a magnetic medium. More particularly, the invention concerns a user programmable control circuit and user interface to optimize write-to-read settling times of such a device.
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 disc, such as a floppy disc or a hard disc for storing programs and data in a computer.
The read channel for a magnetic recording device includes a sensor in the form of a magneto-resistive head in close proximity with the magnetic medium. When the magnetic material is moved relative to the sensor, a flux is induced in the sensor in dependence of the local orientation of the magnetic material, thereby generating an information signal which can be amplified and then decoded.
When information is written in digital form, such as for computer data storage or digital recording of music, a current is generated by a write channel and passed through a thin film head in one direction to write a binary “0” and in the opposite direction to write a “1”. When the medium is read by the sensor, or read 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 by a bit detector.
Hard disk drives typically include multiple magnetic discs, or platters, each side of which are used for reading and writing information. The read heads and write heads are mounted on arms positioned at each side of the disk, and in modern systems, servo patterns are embedded in radial patterns on the disk. Reading and writing are interchanged in conformance with the servo patterns.
Write-to-read settling time is an important specification because it impacts directly with drive capacity. Write-to-read settling time is defined to be the time required for the read channel to settle and be able to read the next servo field after the write channel has stopped writing. The gap on the magnetic disk between the end of the write sector and the start of the servo field is wasted area and hence should be minimized.
The disturbance to the read channel during write-to-read transition comes mainly from three sources. The first source is a flexible cable which is conventionally used to electrically couple the integrated circuit which embodies the read and write channel circuitry to the write heads and read sensors. This cable has multiple conductors in close proximity, which is a source of interference. The circuitry for the write channel and the read channel are typically embodied on a single integrated circuit, referred to in the art as a “preamplifier IC”. The preamplifier IC will have several read and write channels, grouped in read/write pairs for each read/write head combination in the device. The close physical proximity of the read channel circuitry and the write channel circuitry on the integrated circuit is a source of undesired capacitive coupling between the write and read channels. A third source of interference is from the connection pens, bond wires and bond pads on the integrated circuit, which may also be a source of unwanted coupling. The disturbances from each of these sources needs to be suppressed from propagating to the output of the read channel, so as to avoid errors in decoding the information read from the disc. On the other hand, excess suppression will also interfere with the proper reading of actual data.
The exact duration and nature of write-to-read disturbances are somewhat unpredictable. It depends on the assembly of the heads, sensors and flexible cable, as well as other sources as described above, and hence varies between models of hard disk drives assembled by a manufacturer of such devices. When designing a preamplifier IC, the designer must model the interference sources, based on design data provided by the disk drive manufacturer as well as past experience (if any) with other models of that manufacturer, to design a suitable filter for interference suppression for the read channel. After fabricating the preamplifier IC, the IC is tested in the intended hard disk of the manufacturer. If there is too little suppression or too much suppression, unacceptable read errors will occur and the designer will have to redesign the filters in the IC, necessitating changes to the mask set for the IC as well as re-fabrication of the preamplifier IC with the revised filters. Such an iterative process undesirably lengthens the design cycle, increasing costs for both the IC manufacturer and the manufacturer of the hard disk drive or other magnetic storage device.
Even after arriving at a suitable design for the preamplifier IC, the hard disk drive manufacturer still faces problems with chip-to-chip variations in the pre-amplifier ICs, as well as drive-to-drive variations in the assembly of the read sensors, write heads, flex cables and their interconnection with the preamplifier IC. While all elements may be “within spec”, the combination of several elements near their outer tolerance limits will often yield a hard disk drive with a read error rate outside of acceptable limits.
In the present state of the art, suitable tools are not available to the IC manufacturer to avoid the above-mentioned iterations in the design cycle nor for the drive manufacturer to easily fix read error problems arising from normal chip-to-chip variations and variations in the head/sensor/cable interconnect.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a magnetic storage apparatus in which the manufacturer or other user may optimize the performance of the read channel before, during or after assembly. There is also a need for a magnetic storage apparatus with a control device in the read channel which is user programmable to reduce write-to-read settling time in an efficient manner. Additionally, there is a need for an integrated circuit having a read channel which can be programmed by the manufacturer of the integrated circuit or the manufacturer's customer to optimize write-to-read settling time.
These and other objects of the invention are satisfied according to a first aspect of the invention in which a magnetic information storage apparatus includes a write channel for writing information to a magnetic medium and a read channel for reading information from the magnetic medium. The read channel includes a sensor which generates an information signal in response to information stored on the magnetic medium and a signal path which amplifies the information signal from the sensor and provides an amplified information signal. The signal path has at least one control device which controls a zero of the signal path in a time-dependent manner, the control device being programmable to control the time dependent response of the zero.
When transitioning from a write mode in which the write channel is active to a read mode in which the read channel is active, the transition typically induces a write-to-read disturbance in the read channel. By placing an externally programmable control device in the read channel, the read channel can be adapted to variations which occur from model-to-model of a magnetic storage apparatus of a particular manufacturer. Alternatively, the read channel can be adapted to differences between magnetic storage devices of different manufacturers, so that a supplier of preamplifier IC's can satisfy the needs of multiple customers with only one integrated circuit design. Finally, it is now feasible for a manufacturer of magnetic storage devices to optimize performance to account for unit-to-unit variations within a model type.
Favorably, the programmability is accomplished via a user interface, such as a serial interface
Allouche David
Bhandari Sanjay M.
Pu Dennis
Davidson Dan I.
Hudspeth David
Koninklijke Philips Electronics , N.V.
LandOfFree
Magnetic medium storage apparatus with read channel having a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic medium storage apparatus with read channel having a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic medium storage apparatus with read channel having a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893343