Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of the amplifier
Reexamination Certificate
2001-04-12
2003-12-30
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of the amplifier
C360S046000
Reexamination Certificate
active
06671118
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data storage systems and, in particular, to providing common mode termination for a write head.
BACKGROUND OF THE INVENTION
In disc drives and other data storage systems, digital data is written to and read from data storage surface. Read and write operations are performed through a transducer which is typically carried on a slider body. The slider and the transducer are sometimes collectively referred to as a head, and typically, a single head is associated with each data storage surface. Data are stored by magnetizing the disc storage surface in one of two possible orientations to indicate either a logic 0 or a logic 1. This is referred to as a “write” operation. When writing data, the head carries a current which creates a magnetizing force large enough to saturate the magnetic medium. A write current source with a current return path forms a write circuit that provides write current to the head.
Ideally, the write current source should provide a purely differential write signal to the load (head). However, the circuit topology, manufacturing process and circuit parasitics introduce aberrations in elements of the write circuit. Consequently, in addition to the differential signal provided to the load, an undesirable common mode signal is also present in the write circuit. In current non center tapped heads used in disc drives, the common mode signal does not have a return path. Absence of a return path results in the impedance seen by the common mode portion of the write driver (write current source and current path) to behave like an open circuit stub. Open circuit stubs behave like tuned circuits with series and parallel resonance occurring at ¼ wavelength and ½ wavelength respectively. In a typical flex circuit used in disc drive products, series resonance occurs approximately 500 MHz with an impedance magnitude of approximately 1 ohm which is essentially a short circuit. It is this low impedance value of the series resonance portion of the common mode impedance that can adversely effect active components of the write circuit. If the signal bandwidth of the common mode portion of the write circuit includes, or goes beyond, the series resonance of the common mode impedance loading the write amplifier, uncharacterized write amplifier performance will result because of its inability to drive exceptionally low common mode impedances.
Design constraints make it difficult to use a write amplifier having minimal or zero common mode output, or a write amplifier capable of driving very low values of impedance.
The present invention addresses these problems, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
The present invention relates to data storage systems that include common mode termination for a write head which solves the above-mentioned problem.
A disc drive storage system and device is provided in which uncharacterized behavior of a signal source caused by having to drive a very low impedance due a common mode component of the drive signal is eliminated. A write head that has a first and second end writes on a disc surface. A signal source provides a drive signal to the write head. The drive signal has a differential signal component and a common mode signal component. An electrical interconnect path couples the write head and the signal source. The electrical interconnect path provides a return path for the differential signal component and an open circuit for the common mode signal component. A common mode termination network with a first node, second node and a center tap is included. The first node is connected to the first end of the write head, the second node connected to the second end of the write head and the center tap connected to ground to provide a return path for the common mode signal component. In addition, a method of providing a return path for a common mode signal in a disc drive storage system is provided.
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Putnam John S.
Sorenson Gary D.
Holder Regina N.
Westman Champlin & Kelly
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