Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-08-02
2001-09-04
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S423000
Reexamination Certificate
active
06285221
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to drivers for inductive devices, and particularly to write drivers for inductive magnetic heads.
Inductive magnetic heads are commonly used in magnetic disk drives for writing data to magnetic disks. The magnetic head is operated by driving a write current through the inductive coil of the magnetic head, and reversing the direction of the current to reverse the magnetic field generated by the head. Field reversals induce changes in magnetic dipoles on the disk to represent data. While several types of current driver circuits are commonly used to drive current in opposite directions through the coil, one common circuit is an H-bridge. An H-bridge employs four transistor switches operated to direct write current through alternating pairs of the switches of the circuit. For optimal performance, the rise time of the write current at transitions should be as short as possible. Extended rise times adversely affect the field reversal characteristics and the recorded data. Current overshoots are often avoided because current overshoots usually generate undesirable undershoot, thereby creating ringing and increasing the settling time of the write current. While current overshoot is not necessarily an undesirable phenomenon, as overshoot often leads to quicker rise times, the undershoot delays settling time of the steady state write current thereby prohibiting implementation of short write current pulses.
Various techniques have been employed to suppress ringing in write driver circuits. Many of these techniques degrade the write current. For example, shunt impedances placed in parallel to the head coil suppress ringing, at the cost of diverting write current through the shunt impedance, making the diverted current unavailable to perform a write function at the head.
As technology of magnetic disk drives advances, it becomes increasingly desirable to increase data recording frequency, to thereby increase data density on the disk. Increased data frequency requires shorter and more rapid rise times to the write current pulses with quicker settling to the steady state write current value and without ringing. The present invention is directed to a technique for minimizing the rise time of the write current pulse and to reduce settling time.
BRIEF SUMMARY OF THE INVENTION
One aspect of the invention is directed to a write driver that includes first and second load terminals for connection to an inductive load, such as a write head of a disk drive. A driver circuit is connected to the first and second load terminals and is responsive to a first control signal to supply a drive current through the load in a first direction and is responsive to a second control signal to supply the drive current through the load in a second, opposite direction. A voltage-mode H-bridge is connected to the first and second load terminals to selectively supply a voltage across the load terminals and head. Program means is responsive to the first and second control signals to operate the voltage-mode H-bridge to supply the voltage to the respective first and second load terminals for a predetermined time period following a data transition (represented by an initiation of the respective first and second control signal) to quickly raise the write current to a steady state condition.
An optional feature of the voltage-mode H-bridge is the operation of the program means to provide the voltage to the load terminals for a first predetermined time period to shorten the rise time of the write current at the transition, and then reverse the voltage for a second predetermined time period to correct overshoot of the write current and assure formation of a narrow overshoot pulse and rapid settling to the steady-state write current of the driver.
Another aspect of the invention is directed to a write driver that includes first and second load terminals for connection to an inductive load. The inductive load includes an inductive write head of a disk drive and a transmission line of predetermined impedance connected to the write head for connection to the first and second load terminals. An impedance-matched driver circuit is connected to the first and second load terminals and is responsive to a first control signal to supply drive current through the load in a first direction and is responsive to a second control signal to supply drive current through the load in a second, opposite direction. The driver circuit has an impedance matched to the impedance of the transmission line to suppress ringing.
One form of the impedance-matched driver circuit is an impedance-matched H-bridge. The impedance comprises a first impedance connected between first load terminal and the junction of two transistors forming one leg of the H-bridge, and a second impedance connected between the second load terminal and the junction of two transistors forming the other leg of the H-bridge. Preferably, the first and second impedances have substantially equal impedance values.
In a preferred form of the invention, the impedance-matched driver circuit and the voltage-mode H-bridge are used together for optimal performance. The transmission line to the head has a predetermined propagation time of signals between the load terminals and the head. For optimal performance, the predetermined time period of operation of the voltage-mode H-bridge is no greater than twice the predetermined propagation time of the transmission line, thereby avoiding reflection of differential voltage supplied by the voltage-mode H-bridge. Moreover, the impedance-matched driver circuit is responsive to the respective first and second control signals to supply drive current to the respective first and second load terminals and sink drive current from the respective second and first load terminals for a period of time of about twice the predetermined time period of operation of the voltage-mode H-bridge.
REFERENCES:
patent: 5126603 (1992-06-01), Hattori
patent: 5379209 (1995-01-01), Goff
patent: 5550502 (1996-08-01), Aranovsky
patent: 5880626 (1999-03-01), Dean
patent: 6052017 (2000-04-01), Pidutti et al.
patent: 6101052 (2000-08-01), Gooding et al.
Groen Eric
Leighton John D.
Agere Systems Guardian Corp.
Kinney & Lange , P.A.
Zweizig Jeffrey
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