Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-03-31
2001-02-20
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06191643
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present invention is related to an invention that is the subject matter of a commonly-assigned co-pending application entitled “Architecture for Hard Disk Drive Write Preamplifiers”, filed concurrently herewith, which is incorporated by reference herein and is also related to an invention that is the subject matter of a commonly-assigned co-pending application entitled “Fast High Side Switch for Hard Disk Drive Preamplifiers”, also filed concurrently herewith, also incorporated by reference herein.
FIELD OF THE INVENTION
The present invention relates generally to the field of preamplifiers within magnetic storage systems and, more particularly, to voltage boost circuitry for preamplifiers within magnetic storage systems.
BACKGROUND OF THE INVENTION
Rotating magnetic disk data storage devices are known in the art. In these devices, one or more read/write heads, typically inductive heads, are used to store data and read data from an associated disk media surface. More specifically, a read/write head is passed over a magnetic medium and transduces the magnetic transitions into pulses of an analog signal that alternates in polarity.
The signals to and from a head-disk assembly of a hard disk drive are then processed mainly by a preamplifier (write driver), i.e., the preamplifier receives from an associated channel device both data signals to be written onto a disk surface during a write operation and control signals used to specify the individual head to be selected for a read or write operation.
Write speeds in hard disk drive preamplifiers are continually improving. An inductive write head includes an inductive coil that can change the localized magnetic fields on the magnetic data-storage medium and thus allows the digital data to be recorded. The speed of this recording process (i.e., the write speed) is determined by how fast the current in a hard disk drive write head can be reversed (the polarity of the write current through the write head being reversed in response to the bit pattern of the information signal). This is also referred to as the “rise-time.” Typically the desired requirements for the write driver are a large current capability (e.g., 40-80 ma) combined with a fast rise time (e.g., 1-4 ns) for driving the inductive write head.
The write head for a disk data storage device can be approximately modeled by an inductor with an inductance of L. The voltage across an inductor is ideally proportional to the rate of change of the current through the inductor in time. The mathematical expression for this voltage is given as V
L
=L di/dt. Essentially, the voltage across the inductive write head, V
L
, is proportional to the value of inductance, L, and to the speed at which the write current is reversed, di/dt. This means that the write current reversal time in inductive write-heads fundamentally depends on how large a voltage can be impressed across the write drive head. Normally, the voltage across the inductor is limited by the supply voltages. Thus, either the head inductance value should be decreased, or, the supply voltage should be increased, to improve the write speed. The first option, decreasing the head inductance value, is normally not preferred, as it negatively affects the reliability of the data-recording process.
Conventional techniques use the power supply to generate the voltage across the inductor. However, the voltage supply limits the voltage that can be applied across the inductor and therefore limits the rise time. Higher write speeds require higher supply voltages. However, the second alternative, increasing the supply voltage, may not always be possible, as system-wide considerations dictate the selection of power supply voltages, and the present trend in fact is the reduction of power supply voltages.
The present invention is therefore directed to the problem of developing a hard disk drive preamplifier that satisfies the demand for improved rise-time while meeting the conflicting demand for maintaining a same supply voltage.
SUMMARY OF THE INVENTION
The present invention solves these problems by providing a novel method and architecture for improving the rise-time in a preamplifier so as to provide faster write speeds in disk data storage devices. In particular, a very high speed charge pump, with enough charge stored, is provided to supply current to the inductive write head.
The present invention provides a preamplifier/write driver (also known in the art as simply a preamplifier), for use with a disk drive assembly, incorporating voltage boost circuitry within the preamplifier, to provide a reduced rise time and therefore a faster write speed.
In one embodiment of the present invention, a boost circuit, for a preamplifier having a mode of operation for providing a boost voltage to reverse the current in an inductive write head, includes a first switch having a first terminal and a second terminal, the second terminal coupled to ground, a first npn transistor, a capacitive element coupled between the emitter of the npn transistor and the first terminal of the first switch and a second switch having a first terminal coupled to a supply voltage and second terminal coupled to the first side of the first switch. The capacitor is charged to a voltage equal to the supply voltage minus the voltage drop across the npn transistor by closing the first switch and opening the second switch. A boost voltage to reverse the current in the inductive write head is then generated by opening the first switch and closing the second switch.
In one particular embodiment, the first switch is driven by an emitter-coupled pair of transistors and in yet a further embodiment, the collector terminal of the first switch is clamped by an npn transistor thereby preventing the transistor from entering the deep saturation region of operation.
In a second embodiment of the invention, a voltage boost circuit for increasing a preamplifier current, includes a charge storage device for storing a charge, a timing controller coupled to the charge storage device, a voltage source coupled to the charge storage device and to the timing controller, the voltage source charging the charge storage device under the control of the timing controller, and an adder coupled to the charge storage device, to the timing controller and to the voltage source, the adder summing the voltage stored in the charge storage device and the voltage source under the control of the timing controller.
From a method standpoint, the invention includes a method of intermittently increasing an internal nodal voltage in a preamplifier of a disk data storage device, the method comprising the steps of charging a capacitor by closing a first switch and opening a second switch, the first switch having a first side connected to the low voltage side of the capacitor and a second side connected to ground, and the second switch having a first side connected to a supply voltage and a second side connected to the first side of the first switch, and, opening the first switch and closing the second switch, the low voltage side of the capacitor being driven high and the high voltage side of the capacitor going above the supply voltage, thereby supplying the current needed to reverse the current in the inductor.
In a particular embodiment of the invention, the first switch is an npn transistor and during the charging step, the base of the first switch is pulled high.
The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however may be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5581455 (1996-12-01), Rossi et al.
patent: 5604671 (1997-02-01), Okamura
patent: 5689208 (1997-11-01), Nadd
patent: 5812015 (1998-09-01), Tobita
patent: 6060948 (2000-05-01), Tarantola et al.
Eskiyerli Murat Hayri
Nayebi Mehrdad
Shapiro Phil
Mayer Fortkort & Williams LLC
Sony Corporation
Williams, Esq Karen L.
Zweizig Jeffrey
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