JPH11149605A - Method and circuit enabling quick magnetic flux inversion in coil of write head related to computer disk driving device or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly drive the coil of a write head by connecting transistors passing additional currents parallely with lower side transistors constituting an H dridge driving the coil of the write head and making the leading edge of the pulse of a coil current overshoot temporarily. SOLUTION: Additional transistors 60, 62 receive inverted input signals of signals being on input lines 51, 52 via variable capacitors 64, 66 to be switched simultaneously with lower side transistors 47, 49 to pass additional currents with respect to a coil 50. The additional currents by ways of the transistors 60, 62 do not receive the restriction of the Miller current of a reference current source 70. Then, the current of the coil 50 is made to overshoot temporarily by setting the variable capacitors 64, 66 in proper ratios with respect to variable capacitors 54, 56 and passing the additional currents by ways of the transistor 60, 62 only in parts of desired ratios during desired transition time by the lower side transistors 47, 49.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a method and a circuit for driving an inductive load or the like in which it is desired to apply a signal having a fast rise time, that is, a rise time. Relates to improvements in methods and circuits for driving inductive loads of the type used in connection with write heads, such as disk drives.

[0002]

BACKGROUND OF THE INVENTION Most computer systems include one or more computers which can be built into the computer system or provided externally to the system which connects to the system via known means. An associated disk drive or disk drive is included. Typically, a disk drive has at least one rotating magnetic medium and an associated head mechanism carried adjacent the medium. The head may be radially positioned to selectively write information to or read information from precise locations on the disk media. Such a disk drive can be, for example, a so-called hard disk drive, a floppy disk drive, or the like.

Data is written to an associated data disk by applying a series of signals to a write head in accordance with digital information to be stored on a magnetic disk medium. The write head has one or more associated pole pieces located proximate to the coil and the disk media. As the magnetic flux changes in the head, the magnetic domains of the magnetic media of the disk are aligned in a predetermined direction for a subsequent read operation. Typically, a small space separates each magnetic domain transition, allowing successive transitions on the magnetic medium to be distinguished from each other.

[0004] Because the disk moves relative to the head, difficulties may be encountered in distinguishing successive magnetic transitions if the small space separating each magnetic domain transition is not large enough. It is possible to understand that there is. This can cause errors when reading data contained on the disk, which is, of course, undesirable.

On the other hand, as computers become faster and faster, it becomes increasingly important to increase the speed at which data can be written to disk media. However, since the data signal is in the form of a square wave transition, if the rise time of the square wave tip is large, the small space between the magnetic medium transitions will be large, which means that the data will be accurate. To reduce the effective speed at which data can be written and read. Because the write head assembly has at least one coil, it is difficult to force the current to rise quickly in the write head, i.e., to reverse the direction of the magnetic flux.

Conventionally, a data write circuit used to supply such a write signal to a head can enable current reversal at a relatively high speed for accurate data reproduction. A preamplifier circuit is provided to drive current through selected circuit branches of the "H-bridge" circuit.

Accordingly, a method and circuit for driving an inductive load of the type used in connection with a write head of a disk drive associated with a computer or the like, with a signal enabling a maximum flux reversal rate in the driver coil. It is desired to provide

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a method and a circuit for driving an inductive load, which overcome the above-mentioned disadvantages of the prior art. Aim. It is another object of the present invention to provide a method and circuit for driving an inductive load of the type used in conjunction with a disk drive or write head of a disk drive in connection with a computer or the like. That is.

It is another object of the present invention to provide an inductive load of the type used in connection with a write head of a disk drive associated with a computer or the like with a signal that allows maximum flux reversal speed in a driver coil. Is to provide a method and a circuit for driving.

It is yet another object of the present invention to provide a method and circuit for driving an inductive load with a signal having a fast rise time.

It is yet another object of the present invention to drive an inductive load that allows data to be written faster at a more accurate data transition on a recording medium than a typical H-bridge driver. To provide a method and circuit for doing so.

[0012]

SUMMARY OF THE INVENTION In accordance with the present invention, a head mechanism is provided for initiating flux reversal within a coil of a head assembly much more quickly than would occur if only normal H-bridge technology was used. A circuit is provided that provides a measured amount of initial "overshoot" current to the pulse applied to the coil. Thus, in accordance with a broad aspect of the invention, there is provided a circuit for applying a current to a coil of a write head assembly of a computer disk drive to rapidly change the direction of magnetic flux in the coil of the head assembly. . The circuit includes a circuit that generates at least one current pulse that is supplied to a write coil to initiate a magnetic flux in a desired direction within the coil. Further, the circuit includes a circuit for introducing an overshoot current on the tip of the at least one current pulse to quickly initiate a flux reversal within the coil of the head assembly.

According to another broad aspect of the invention, each pair is connected between a supply voltage and a reference voltage and is adapted to be connected to a coil between two transistors of each pair. An apparatus is provided for applying current to a write coil of a write head assembly using an H-bridge of the type having two pairs of two switchable transistors. A first pair of two transistors is controlled to turn on a complementary transistor of the first and second pair of transistors to selectively control current flow in the coil in the first or second direction. It is adapted to be connected to receive a signal. A reference current source supplies the reference current and one of the transistors in each of the first and second pairs is connected to mirror the reference current to control the current in the coil when turned on. Is done.
First and second parallel transistors are respectively connected in parallel with the mirror transistor, and the first and second parallel transistors are connected to be turned on by the control signal and the inversion control signal, respectively, simultaneously with the respective mirror transistors. I have. A pair of timing elements turns off each of the parallel transistors after a predetermined time, so that when the parallel transistors are turned on, the current in the coil will overshoot by the value established by the mirror transistor.

In accordance with another broad aspect of the present invention, there is provided an apparatus for applying current to a write coil of a magnetic head assembly. The device has an H-bridge, which has first and second current paths, each current path including a write coil. First and second mirror transistors, which are selectively turned on in response to the control signal and the inverted control signal, respectively, provide first and second currents for monitoring a reference current to control the current in the write coil. Each is connected in the route. First and second current boost transistors are connected in parallel with the first and second mirror transistors, respectively, and are connected to be turned on simultaneously with the first and second mirror transistors. The first and second current boost transistors apply a boost current to the write coil for a predetermined time after being turned on.

[0015] Capacitors are connected to respective control elements of the first and second current boost transistors to control the time that the current boost transistor is turned on at a level higher than the current level of the mirror transistor.

In accordance with yet another broad aspect of the present invention, there is provided an apparatus for generating an overshoot current in a coil connected across an H-bridge when a current direction transition occurs. The apparatus has a reference current generator connected to the H-bridge current control transistor in such a manner that the current control transistor mirrors the current of the reference current generator. A pair of parallel transistors are connected in parallel with each of the current control transistors that are simultaneously switched on with each of the current control transistors, and the time during which the parallel transistors conduct at a current level higher than the current level of the current control transistor. A timing element is connected to the parallel transistor for limiting.

In accordance with yet another broad aspect of the invention, there is provided a method for generating an overshoot current in a coil connected across an H-bridge when a current direction transition occurs. The method includes monitoring a reference current in a current control transistor of the H-bridge and providing a pair of parallel transistors in parallel with each of the current control transistors. The method further includes timing the conduction of the parallel transistors to switch the parallel transistors simultaneously with each current control transistor and to limit the time the parallel transistors conduct at current levels higher than the current level of the current control transistors. It includes taking.

In accordance with yet another broad aspect of the invention, a method is provided for increasing the speed at which magnetic flux in a write head associated with a computer hard disk drive is reversed. The method includes monitoring a reference current in a current control transistor of the H-bridge to control a current level in the coil, and providing a pair of parallel transistors in parallel with each of the current control transistors.
The method further includes turning on the parallel transistors simultaneously with each of the current control transistors and limiting conduction of the parallel transistors at a current level higher than the current level of the current control transistors to limit the time that the parallel transistors conduct. Includes timing.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A type for supplying a write signal to a magnetic head assembly of the same type as described in the applicant's patent application filed concurrently with the present application. An example of a typical H-bridge coil drive circuit 10 is shown in FIG. Circuit 10 comprises an H-bridge driver circuit, which has four transistors 12-15 connected between _Vcc rail 11 and ground 17. For example, a coil 19 used to provide magnetic flux as part of a write head mechanism, as shown, is H
It is connected between the central circuit branches of the bridge circuit 10.

As will be appreciated, each transistor 1
Depending on the gate bias applied to 2-15, current may flow through coil 19 in one direction or another. That is, one current path includes a transistor 14, a right-to-left coil 19, and a transistor 13, and another current path includes a transistor 12, a left-to-right coil 19, a transistor 15 are included.

The conduction of transistors 12-15 is controlled by respective driver controlled inverter circuits 21 and 22, each of which is a pair of transistors 23-24 connected between V _CC 11 and ground 17, respectively. And 26
-27. Therefore, transistors 12-15
Is controlled by the state or voltage applied to input lines 28 and 29, respectively. As can be seen, the signals applied to input lines 29 and 28 are out of phase with each other, so that either set of transistors 13 and 14 or set of transistors 12 and 15 are conductive,
Neither set will be conducting at the same time.

The gates of the transistors 13 and 15 are connected to a reference current source 37 by transmission gates 33 and 35, respectively.
Is selectively connected to the gate of the transistor 38 through which the current flows. Thus, transistors 13 and 15 can be selected to form a current mirror with transistor 38 to mirror the reference current flowing through transistor 38. Therefore, by selectively operating the transmission gate 33 or 35,
The current flowing through either transistor 13 or 15 is controlled to a predetermined level, thereby controlling the magnitude of the current flowing in coil 19.

Thus, the magnetic flux in the coils of the head mechanism associated with circuit 10 can be reversed by applying appropriate signals to input lines 28 and 29. However, as the data rate increases, the speed at which the head can write data to the magnetic media is limited by the speed at which the flux head can flip, especially when the data rate is the maximum physical flux of the driver circuit. This can be said as the reversal speed approaches.

Referring now to FIG. 2, there is shown a schematic diagram of a write coil driver 45 according to the present invention. The write coil driver circuit 45 is an H bridge driver circuit 43
Which has four transistors 46-49. Transistors 46-49 are connected between V _CC and ground, transistors 46 and 47 are in series, and transistors 48 and 49 are in series.

Transistors 46-49 are selectively conductive to direct current through coil 50 associated with a magnetic write head mechanism, such as those used in connection with computer disk drives and the like. Switch operation is possible. Thus, depending on which pair of transistors 46-49 or 48-47 are currently conducting, current will flow in the corresponding direction in coil 50 in the same manner as described above with respect to FIG.

Each pair of opposing transistors in H-bridge 43 is controlled by input signal VCDI on line 51 and VCDI_ on line 52. It should be noted that an underlined character after the English character symbol indicates that the signal of the English character symbol is an inverted signal. Signals VCDI and VCDI_ are applied to the gates of transistors 46 and 47 on the left side of circuit 45 and the gates of transistors 48 and 49 on the right side of circuit 45, respectively. The inverted signals on lines 51 and 52 serve to control the switching time and the transistors 47 and 49, respectively, by the variable capacitors 54 and 56, which serve to isolate the gate of the lower transistor from the respective inverter after switching has occurred. Is applied to the gate of

According to the invention, an additional transistor 6
0 and 62 are connected in parallel with the respective transistors 47 and 49. The gates of transistors 60 and 62 are connected to input line 51 by respective variable capacitors 64 and 66.
And 52 to the inverted input signal.

Finally, the circuit 45 is provided with a reference current source 70 which acts as a reference current for the mirrored current to control the current in the coil 50. A reference current transistor 71, through which a reference current flows from current source 70, has its gate connected to the gate of transistor 47 by transmission gate 72 and to the gate of transistor 49 by transmission gate 74. Transmission gates 72 and 74 are connected to respective transistors 71
Each of the gates is controlled by the state of the inverted signal on the input line 51 in order to connect the gates of 47 to 49 or 49 respectively. Therefore,
When either transmission gate 72 or 74 is turned on, the respective lower transistor 47 or 49 is connected to mirror the current flowing through transistor 71. Thus, the upper transistors 46 and 48 of the H-bridge 45 basically act as switching transistors, while the lower transistors 47 and 49 control the magnitude of the current flowing through the write coil 59 precisely. Works.

Since transistors 60 and 62 are connected directly to their respective control lines 51 and 52 by capacitors, they switch simultaneously with lower switch transistors 47 and 49, but are limited by current. is not. Therefore, the transistor 60 or 6
When either of the two is switched on, the switched on transistor allows additional current flow through the coil 50 until charge is stored on its respective gate capacitor. After that point, the current in transistor 47 or 49 controls the current through coil 50. The values of capacitors 64 and 66 are selected such that transistors 60 and 62 are turned on for a predetermined percentage of the transition time when respective parallel transistors 47 or 49 are turned on. As a result of the transistor 60 or 62 being turned on for a predetermined fraction of the transition time, additional current is drawn through the write coil 50 during the transition of the current.
This temporary overdrive current applies an overshoot current to the write head, increasing the speed at which the magnetic flux in the write head reverses. As will be appreciated, the ratio of the width to length dimensions of transistors 47 and 60 and transistors 49 and 62 will depend on the amount of excess current provided by the modified bridge and the corresponding over current supplied to the write head coil. Define the shoot current. The ratio of the variable capacitors 64 and 66 to their associated transistor 60 and 62 gate capacitances defines the precise amount of current overshoot.

The voltage waveforms obtained using the circuit 45 of the present invention are shown in FIGS. In FIG. 3, the upper waveform shows the overshoot voltage V _GS , and the lower waveform shows the voltage V _GS which is the exact boost voltage across the lower transistors 47 and 49 in FIG. ing.

The corresponding inductor current generated for the overshoot and the exact boost condition of FIG. 3 are shown in FIG. Due to parasitic capacitance, the write coil of the head assembly provides an LC system rather than a simple inductor. Thus, the current through the coil may have some oscillation as will be appreciated. This oscillation frequency does not depend on the current program value.

For example, compared to the exact boost case, one advantage of the overshoot technique of the present invention is that the value of the inductor current during the undershoot, which is about half of the programmed current, demagnetizes the head and Data written during the first overshoot period may be erased. This phenomenon also reduces the writing frequency. In this regard, the overshoot condition is more secure, where the current during the first undershoot is about 80% of the programmed current.

Another advantage of the overboost technique of the present invention is that the magnetic inertia of the pole piece of the head mechanism, which operates almost like a low pass filter, is eliminated. By overdriving the current to the coil provided in the head mechanism, the rise time of the magnetic flux can be significantly increased.

Although the specific embodiments of the present invention have been described in detail above, the present invention should not be limited only to these specific examples, but may be variously modified without departing from the technical scope of the present invention. Of course is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an H-bridge circuit for driving an inductive load.

FIG. 2 is a schematic diagram showing a write coil drive circuit configured based on the present invention.

FIG. 3 is a waveform diagram showing V _GS of a lower switching transistor, wherein the lower half graph shows the exact boost effect and the upper half graph shows the over boost.

FIG. 4 is a waveform diagram showing inductor current showing the effect of over-boost current for rapid magnetic flux reversal.

[Explanation of symbols]

10 H bridge coil drive circuit 11 V _CC rail 12-15 Transistor 17 Ground 19 Coil

 ──────────────────────────────────────────────────続 き Continuing the front page (72) Inventor Axel Alegre de la Sujoul United States, California 95066, Scotts Valley, Apple Valley Road 32 (72) Inventor Albino Pidutti Italy, 33100, Udine, Via Oppi 42 (72) Inventor Erango Pacriswamy USA, California 95051, Santa Clara, Halford Avenue 1901, number 102

Claims (24)

[Claims] 1. An apparatus for applying current to a coil of a write head assembly, wherein an H-bridge comprising two pairs of two switchable transistors is provided, each pair comprising a supply voltage, a reference voltage and a reference voltage. And adapted to connect a coil between the two transistors of each pair, the first pair of two transistors turning on one of the first pair of two transistors. And adapted to be connected to receive a control signal to turn off the other one of the first pair of two transistors, wherein the second pair of two transistors is of the first pair of two transistors. Are turned on and connected to receive an inversion control signal for turning off the other of the two transistors of the second pair. In this case, when the one transistor of the first pair is turned on and the other transistor of the second pair is turned off, a current flows in the coil in a first direction; When a pair of the other transistors are turned on and the one transistor of the second pair is turned off, a current flows in the coil in a second direction, and a reference current source for supplying a reference current is provided. Wherein one of the transistors in each of the first and second pairs is connected to mirror the reference current when one of the transistors is turned on, whereby the current in the coil is controlled by the reference current; And a transistor in the first and second pairs, wherein a second parallel transistor is connected to mirror the reference current. And the first and second parallel transistors are respectively connected in parallel with the transistor, and the control signals and A pair of timing elements that are connected to be turned on by the inversion control signal and turn off each of the parallel transistors after a predetermined time, and that when the parallel transistors are turned on, Apparatus, wherein the current overshoots by a value established by said mirror transistor. 2. The apparatus according to claim 1, wherein said timing elements are capacitors connected to respective control elements of said parallel transistors. 3. The apparatus of claim 1, wherein said two pairs of two switchable transistors of said H-bridge and said first and second parallel transistors are MOS transistors. 4. The method of claim 1, wherein the one of the transistors in each of the first and second pairs of transistors is connected to the reference current by a transmission gate, the reference gate being connected to the control signal and the control signal. Apparatus characterized in that each is controlled by an inversion control signal. 5. The method of claim 1, wherein an additional timing element is connected to control the mirror transistor to provide an initial amount of current overshoot to the coil. apparatus. 6. Apparatus according to claim 5, wherein said additional timing elements are capacitors connected to respective control elements of said mirror transistor. 7. An apparatus for applying a current to a write coil of a magnetic head assembly, comprising: an H-bridge including first and second current paths each including the coil; First and second mirror transistors are provided that are selectively turned on in response to respective inversion control signals, the mirror transistors being configured to mirror a reference current to control a current in the coil. First and second current paths, respectively, connected in parallel with the first and second mirror transistors, and connected to be turned on simultaneously with the first and second mirror transistors. First and second current boost transistors are provided, and the first and second current boost transistors are turned on at a predetermined time after being turned on. Applying a boost current to said coil for a period of time. 8. The control element of claim 7, further comprising a control element for controlling the time at which the current boost transistor is turned on at a level higher than the current level of the mirror transistor. An apparatus characterized in that a capacitor is connected to the device. 9. The apparatus of claim 7, wherein said first and second mirror transistors and said first and second current boost transistors are MOS transistors. 10. The method of claim 7, wherein the mirror transistor is connected to the reference current by a transmission gate,
Apparatus, wherein the reference gate is controlled by the control signal and the inversion control signal, respectively. 11. The apparatus of claim 7, further comprising an additional timing element connected to control the first and second mirror transistors to provide an initial amount of current overshoot to the coil. An apparatus characterized by the above. 12. The apparatus according to claim 11, wherein said additional timing element is a capacitor connected to respective control elements of said first and second mirror transistors. 13. An apparatus for generating an overshoot current in a coil connected across an H-bridge by a current direction transition, wherein the current control transistor mirrors the current of a reference current generator. A reference current generator is connected to the current control transistors of the bridge, and each of the current control transistors and a pair of parallel transistors are connected in parallel to be simultaneously switched on by the respective current control transistors; Apparatus, characterized in that a timing element is connected to the parallel transistor to limit the time that the parallel transistor conducts current at a current level higher than the current level of the current control transistor. 14. The apparatus of claim 13, wherein said timing elements are capacitors connected to respective control elements of said parallel transistors. 15. The apparatus according to claim 13, wherein said current control transistor and said parallel transistor are MOS transistors. 16. The method of claim 13, wherein said current control transistor is connected to said reference current generator by a transmission gate, said reference gate being controlled by an H-bridge control signal and an inverted H-bridge control signal, respectively. An apparatus characterized in that: 17. The apparatus of claim 13, further comprising an additional timing element connected to control the current control transistor to provide an initial amount of current overshoot to the coil. Characteristic device. 18. The apparatus of claim 17, wherein the additional timing elements are capacitors connected to respective control elements of the current control transistor. 19. A circuit for applying a current to a coil of a head assembly of a computer disk drive, comprising: a coil for applying a magnetic flux for recording data on a magnetic medium of the disk drive; A circuit for generating at least one current pulse for supplying to the coil; and a circuit for introducing an overshoot current at a front end of the at least one current pulse to quickly initiate a change in a magnetic flux direction in the coil. A circuit, comprising: 20. A method for generating an overshoot current in a coil connected across an H-bridge when a current direction transition occurs, comprising: mirroring a reference current in a current control transistor of the H-bridge; Providing a pair of parallel transistors in parallel with each of the transistors, switching the parallel transistors simultaneously with the respective current control transistors, wherein the parallel transistors conduct at a current level higher than the current level of the current control transistors; Timing the conduction of the parallel transistor to limit the following. 21. The method of claim 20, wherein timing the conduction of the parallel transistors enables capacitors connected to respective control elements of the parallel transistors to discharge. . 22. The method of claim 20, further comprising providing a transmission gate between the reference current and the current control transistor enabled by an H-bridge control signal. 23. The method of claim 20, further comprising providing an additional timing element to control the current control transistor to provide an initial amount of current overshoot to the coil. Method. 24. A method of increasing the flux reversal speed of a write head associated with a computer hard disk drive, comprising mirroring a reference current in a current control transistor of an H-bridge to control a current level in the coil. Providing a pair of parallel transistors in parallel with each of the current control transistors, switching on the parallel transistors simultaneously with each of the current control transistors, the parallel transistor at a current level higher than the current level of the current control transistors; Timing the conduction of said parallel transistors to limit the time that they conduct.