Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
1999-02-25
2001-03-06
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S424000, C327S110000
Reexamination Certificate
active
06198335
ABSTRACT:
TECHNICAL FIELD
This invention relates to circuits for driving inductive loads and more particularly to a bridge circuit for driving the inductive coil of a magnetic write bead of a disk drive.
BACKGROUND OF THE INVENTION
Most computer systems include one or more associated disk drives, which may be built into or external to the computer system. Typically, disk drives have at least one rotating magnetic medium and associated head mechanisms that are carried adjacent the magnetic material. The heads are radially positionable to selectively write information to, or read information from, precise positions on the disk medium. Such disk drives may be, for example, hard disk drives, floppy drives, or the like.
Data is written to the associated data disk by applying a series of signals to a write head according to the digital information to be stored on the magnetic disk media. The write head has a coil and one or more associated pole pieces that are located in close proximity to the disk media. As signals cause the magnetic flux to change in the head, the magnetic domains of the magnetic media of the disk are aligned in predetermined directions for subsequent read operations. Typically, a small space of unaligned magnetic media separates each magnetic domain transition to enable successive transitions on the magnetic media to be distinguished from each other.
Since the disk is moving relative to the head, it can be seen that if the small space separating the magnetic domain transitions is not sufficiently wide, difficulty may be encountered in distinguishing successive magnetic transitions. This may result in errors in reading the data contained on the disk, which is, of course, undesirable.
Meanwhile, as computers are becoming faster, it is becoming increasingly important to increase the speed at which data can be written to and read from the disk media. However, since the data signals are in the form of square wave transitions, if the rise time of the leading edges of the square waves is large, the small space between magnetic media transitions also becomes large, which reduces the effective rate at which data can be accurately written and read. Since the write head assembly includes at least one coil, forcing the current to rise rapidly, or to reverse flux directions within the write head is difficult.
In the past, data writing circuits used to supply such write signals to the heads included preamplifier circuits to drive the current through selected legs of an “H-bridge” circuit, which is capable of allowing relatively fast current reversals for accurate data reproduction.
As mentioned above, as data rates increase, the rates at which the heads can accurately write the data to the magnetic media is limited by the speed at which the flux in the inductive coil of a write head (and its associated components) can be reversed. The maximum data rate is thus limited to the maximum physical flux reversal rate of the driver circuitry.
What is needed, therefore, is a method and circuit for driving an inductive load of the type used in conjunction with a write head of a disk drive with a signal that enables a maximum flux reversal rate in the driver coil.
SUMMARY OF THE INVENTION
According to one advantage of the invention, a programmable voltage boost circuit for use with an H-bridge circuit is provided. Two transistors are coupled to two respective nodes having an inductive element in between them, and all four transistors are driven by driver circuits. Coupled to one or more of the driver circuits is the programmable voltage boost circuit that has several logic gates, each independently enabled. Attached to the logic gates are capacitors that are connected to the boost circuit output. If the logic gates are enabled, they pull the output toward a pull-up voltage using the selected pull-up capacitors. In one embodiment of the invention, the capacitors have different values and the values are chosen to be binary weighted.
According to another aspect of the present invention, a method of providing a voltage boost to a circuit that drives a transistor in an H-bridge circuit and that has data and program signal inputs begins with providing enabling signals to the voltage boost circuit. Then the voltage boost circuit uses the enabling signals to selectively enable one or more logic gates within the voltage boost circuit and capacitively couples the output of the voltage boost circuit to a pull-up voltage when a valid data signal is received by an enabled logic gate
REFERENCES:
patent: 5309347 (1994-05-01), Poma et al.
patent: 5521547 (1996-05-01), Tsukada
patent: 5834965 (1998-10-01), LeClerc
patent: 5952856 (1999-09-01), Horiguchi
patent: 5990640 (1999-11-01), Dwyer et al.
patent: 6011423 (2000-01-01), Baizley et al.
“Gain of 1 for 5-Volt Read/Write Preamplifiers,” VTC Inc., p. 7-5, Aug. 1994.
Carlson David V.
Dinh Paul
Galanthay Theodore E.
Jorgenson Lisa
STMicroelectronics Inc.
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