Damp circuit for a hard disk drive write head

Details Damp circuit for a hard disk drive write head Damp circuit for a hard disk drive write head

1997-09-19

2001-05-01

Hindi, Nabil (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C360S046000

Reexamination Certificate

active

06226141

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the write driver circuit for a hard disk drive HDD). More particularly, it relates to a damp circuits for minimizing ringing and overshoot while not affecting the tr/tf at the write head when reversing the current through the write head.
BACKGROUND OF THE INVENTION
A hard disk drive storage system typically includes one or more rotating disks, or platters having magnitizible material coated on their surfaces. Read/write heads associated with each platter surface move together radially across the head to reach addressable data regions located on concentric circles called tracks. It is now common to have separate read and write heads. The write head is essentially a small coil of wire which stores data by magnetizing small regions of the disk platter along the tracks. A current driven through the write head creates a temporary magnetic field which magnetizes a small region of the disk at the current position of the write head.
The electronic circuitry used to drive current through the write head typically uses an H-bridge as shown in FIG.
1
. For example, U.S. Pat. No. 5,638,012, issued to Hashimoto et al. and incorporated herein by reference, uses an H-bridge for a write driver circuit. The purpose of the H-bridge is to allow electric current to be driven through the write head in either direction. When the current is driven in one direction a magnetic field is created with the north pole in one direction, and when the current is driven in the opposite direction, a magnetic field is created with the north pole in the opposite direction. The H-bridge operates to switch the drive current through the head by turning on a pair of transistors to allow current to flow in a path from a supply source to ground. For example, current flows through the write head from Hx to Hy when transistors Y are turned on and transistors {overscore (Y)} are turned off. Similarly, current flows the opposite direction when transistors {overscore (Y)} are turned on and transistors Y are turned off. The tr, tf (rise time, fall time) is the time corresponding to the speed at which current can reverse through the inductive load of the HDD write head.
It is desirable to increase the speed of the change of current flow to increase the amount of data that can be stored on a single track of the HDD platter. In order to enhance the preamps write driver performance, the rise time (tr) and fall time (tf) of the write current must decrease without compromising the accuracy of or increasing the transient ringing in the circuit, since increasing the transient ring period on the write current decreases the maximum areal data density.
FIG. 2
illustrates the current waveform for a test input to a typical prior HDD write head.
A prior art circuit for reducing the transient ringing is shown in FIG.
3
. This circuit was combined with the circuit shown in FIG.
1
. The Hx and Hy nodes are connected to the write head in FIG.
1
. In this circuit, during transient rings current is dumped to the write head nodes through Zenner diodes. This circuit was somewhat successful in reducing the transients described above but it increased the capacitance at the write head nodes thereby increasing tr and tf.
SUMMARY OF THE INVENTION
The present invention provides an improved write drive circuit which reduces the ringing and overshoot transients of an H-bridge drive circuit. The invention uses on or more damp circuits which minimizes the amount of capacitance on the outputs of the write driver while still accomplishing the dampening of the transient ring and overshoot. In an embodiment of the present invention, a ring clamp circuit includes a resistor connected to each node of the write head. Each resistor is then connected to the emitter of a npn transistor where the transistors have an enabling gate and a collector connected to a source voltage. The enabling gates may be common and the collector sources may be tied to a common source voltage.
In another embodiment of the present invention, an overshoot damp circuit also includes a resistor connected to each node of the write head. Each resistor is then connected to the emitter of a npn transistor where the transistors have an enabling gate and a collector connected to a source voltage. In the overshoot damp circuit, the resistors, if used, are smaller and the bias voltage of the transistors is chosen to limit the overshoot. Thus essentially the same circuit architecture of the previous embodiment may be optimized to specifically target the ringing or overshoot. In a preferred embodiment, a ring clamp and overshoot circuit are used in combination to control the ringing and overshoot of the write head circuit.
An advantage of the present invention is the head drive current transition time, tr and tf, can be reduced without increasing the transient ring at the head due to a low amount of capacitance added at the circuit nodes Hx and Hy.
Another advantage of the present invention is simplicity of the additional circuit to improve the current transition time while simultaneously reducing transient ring. In addition, the simple circuit according to the present invention decreases the die area needed over prior art circuits.


REFERENCES:
patent: 5430584 (1995-07-01), Petersen
patent: 5517146 (1996-05-01), Yamasaki
patent: 5619386 (1997-04-01), Voorman et al.
patent: 5638012 (1997-06-01), Hashimoto et al.
patent: 5939940 (1999-08-01), Patti

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