Method for active cancellation of write-to-read crosstalk

• US 7,595,949 B1
• Filed: 12/02/2004
• Issued: 09/29/2009
• Est. Priority Date: 12/04/2003
• Status: Expired due to Fees

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Maxtor Corporation (Seagate Technology Holdings Plc)
• Inventors: Gocemen, Ferruh, Wolfson, Jason, Wallash, Albert J.
• Primary Examiner(s): Nguyen; Hoa T
• Assistant Examiner(s): Mercedes; Dismery E
• Application Number:
  US11/001,730
• Time in Patent Office: 1,762 Days
• Field of Search: None
• US Class Current: 360/46
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 2220/2516 Hard disks
• CPC Class Codes: G11B 5/115 Shielding devices arranged between heads or windings G11B5/265 , G11B5/29 take precedence
• CPC Class Codes: G11B 5/3967 Composite structural arrangements of transducers, e.g. inductive write and magnetoresistive read G11B5/3906 takes precedence
• CPC Class Codes: G11B 5/40 Protective measures on heads, e.g. against excessive temperature G11B5/31 takes precedence; protection against wear G11B5/255 ; protective structure of the head: see under structures, e.g. G11B5/3106

Abstract

A method for preventing electrical overstress from interfering with a magnetic read-write device by identifying one or more characteristic functions of the device that characterize electrical overstress, generating a wave form representative of the electrical overstress by using the one or more characteristic functions and enabling the generated wave form to be combined with a read signal to counteract the electrical overstress. The method can be implemented with a crosstalk cancellation circuit that includes a coupler filter configured to receive signals from the write driver, a differentiator to differentiate the signal, a gain adjust coupled to the coupler filter configured to adjust gain on the received signal, a phase adjust configured to adjust the phase to match the crosstalk, and an inverter coupled to invert the matched signal to enable cancellation of the crosstalk. The cancellation circuit can include two components, a first component that addresses common mode crosstalk and a second component that addresses differential mode crosstalk. The combination is added and inverted to enable cancellation of crosstalk in read components of a device.

Claims

1. A method for preventing electrical overstress from interfering with a magnetic read-write device, the method comprising:

identifying one or more characteristic functions of the device that characterize electrical overstress;

generating a wave form representative of the electrical overstress by using the one or more characteristic functions; and

enabling the generated wave form to be combined with a read signal to counteract the electrical overstress,

wherein the generated wave form is a combination of a common mode component and a differential mode component, each of the common mode and differential mode components operated on separately, wherein the identifying and generating steps are implemented in two parts, a first part receiving a write signal representative of capacitive coupling in the device used to generate the differential mode component of the generated wave form, and a second part receiving a write signal representative of inductive coupling in the device used to generate the common mode component of the generated wave form, each of the first and second parts including a gain adjusting step to adjust an amplitude level of the write signal, a phase adjusting step to change a phase of the write signal by a fixed amount and a filtering step to filter excessive signals from the write signal.

2. The method of claim 1 wherein the characteristic function is a transfer function modeling one or more of capacitive coupling and inductive coupling in the device.

3. The method of claim 1 wherein the common mode and differential mode components are operated on using characteristic functions that correspond to the electrical overstress.

4. The method of claim 1 wherein the generated wave form takes into account an operation data rate of the device.

5. The method of claim 1 wherein the magnetic read-write device is a hard drive.

6. The method of claim 1 wherein the generated wave form is an inverted signal to enable the wave form to counteract the electrical overstress.

7. The method of claim 1 wherein the generated wave form is formed by using write signals from a write driver and applying a transfer function to model the electrical overstress from capacitive coupling in the device, the transfer function being proportional to the derivative of the common mode voltage of the write driver with respect to time multiplied by the capacitance caused by the capacitive coupling.

8. The method of claim 7 wherein the transfer function includes:

determining the derivative of the common mode voltage of the write signal with respect to time; and

multiplying by a constant representative of electrical overstress caused by the capacitive coupling.

9. The method of claim 1 wherein the magnetic read-write device includes a crosstalk cancellation circuit including at least two coupler filters, a differentiator, at least two gain adjusters and at least two phase adjusters to produce the generated wave form that matches the electrical overstress.

10. The method of claim 1 wherein the magnetic read-write device is a hard drive on a computer system.

11. A system for counteracting crosstalk in a magnetic read-write device, the system comprising:

a write driver configured to provide signals to a write head;

a crosstalk cancellation circuit coupled to the write driver, the crosstalk cancellation circuit including;

a coupler filter configured to receive signals from the write driver;

a differentiator configured to match crosstalk currents of the signals from the write driver by determining a differential with respect to time for at least two signals from the write driver;

a gain adjust coupled to the coupler filter configured to adjust gain on the received signals;

a phase adjust coupled to the gain adjust configured to adjust the phase to match the crosstalk; and

an inverter coupled to invert the matched signal to enable cancellation of the crosstalk,

wherein the coupler filter, the gain adjust and the phase adjust are adapted to minimize power dissipated in a read head during a write cycle,

wherein the crosstalk cancellation circuit is implemented in two parts, a first part receiving a write signal representative of capacitive coupling in the device, and a second part receiving write signals representative of inductive coupling in the device, each of the first and second parts including a gain adjust, phase adjust and coupler filter.

12. The system of claim 11 wherein the coupler filter is implemented as one or more of a digital filter, analog filter, infinite impulse response filter and finite impulse response filter.

13. The system of claim 11 wherein the coupler filter is a high pass filter with an adjustable bandwidth.

14. The system of claim 11 wherein the coupler filter is adjusted during one or more of once at manufacture and according to an automatic adjustment feedback during operation of a hard drive.

15. The system of claim 11 wherein the crosstalk cancellation circuit is coupled to a summer to add the inverted matched signal to a read signal, the inverted matched signal enabling a near zero net current at a read head of the magnetic read-write device.

16. The system of claim 11 wherein the adaptation to minimize the power dissipated in the read head is accomplished through a gradient descent algorithm.

17. The system of claim 11 wherein the crosstalk cancellation circuit further includes a precision resistance measurement block configured to determine a resistance of a read head.

18. The system of claim 17 wherein the precision resistance measurement block is coupled to a preamplifier, the preamplifier configured to amplify a signal generated by the read head, the precision resistance measurement block detecting existence and changes of any resistance in the read head indicative of crosstalk induced in the read head.

19. A method for preventing electrical overstress from interfering with a magnetic read-write device, the method comprising:

generating a signal representative of any inductive coupling and capacitive coupling signals present on a read head of the magnetic read-write device;

inverting the generated signal; and

adding the inverted signal to the read head to counteract the electrical overstress,

wherein the electrical overstress is caused by capacitive and inductive coupling in the magnetic read-write device caused via write components,

wherein the generating step is implemented in two parts, a first part receiving a write signal representative of capacitive coupling in the device, and a second part receiving write signals representative of inductive coupling in the device, each of the first and second parts including a gain adjusting step to adjust an amplitude level of the write signal, a phase adjusting step to change a phase of the write signal by a fixed amount and a filtering step to filter excessive signals from the write signal.

20. The method of claim 19 wherein generating the signal includes:

receiving write signals generated by a write driver; and

applying a transfer function representative of electrical overstress on the read head.

21. The method of claim 19 wherein the method for preventing electrical overstress is enabled via a crosstalk cancellation circuit, the circuit including at least two filters, a differentiator, at least two gain adjusters, and at least two phase adjusters, the circuit configured to minimize the overstress during a write cycle of the device.

22. The method of claim 21 wherein the circuit applies a gradient descent algorithm.

23. The method of claim 21 wherein the filter is a high pass filter with an adjustable bandwidth.

24. The method of claim 21 wherein the filter operates to differentiate a signal being composed to match the electrical overstress on a hard drive.

25. A computer system comprising:

a processor;

a memory coupled to the processor; and

a magnetic read-write device coupled to the processor, the magnetic read-write device including a crosstalk cancellation circuit coupled to a write driver, the crosstalk cancellation circuit including linear components including;

a coupler filter configured to receive signals from the write driver;

a differentiator configured to match crosstalk currents of the signals from the write driver by determining a differential with respect to time for at least two signals from the write driver;

a gain adjust configured to adjust gain on the received signals;

a phase adjust coupled to the gain adjust configured to adjust the phase to match crosstalk; and

an inverter coupled to invert the matched signal to enable cancellation of the crosstalk,

wherein the crosstalk cancellation circuit is implemented in two parts, a first part receiving a write signal representative of capacitive coupling in the device, and a second part receiving write signals representative of inductive coupling in the device, each of the first and second parts including a gain adjust, phase adjust and coupler filter and further includes a precision resistance measurement block configured to determine a resistance of a read head.

26. The computer system of claim 25 wherein the coupler filter is implemented as one or more of a digital filter, analog filter, infinite impulse response filter and finite impulse response filter.

27. The computer system of claim 25 wherein the coupler filter is a high pass filter with an adjustable bandwidth.

28. The computer system of claim 25 wherein the coupler filter is adjusted during one or more of once at manufacture and according to an automatic adjustment feedback during operation of a hard drive.

29. The computer system of claim 25 wherein the crosstalk cancellation circuit is coupled to an adder to add the inverted matched signal to the crosstalk, the inverted matched signal enabling a near zero net current at a read head of the magnetic medium.

30. The computer system of claim 25 wherein the precision resistance measurement block is coupled to a preamplifier, the preamplifier configured to amplify a signal generated by the read head, the precision resistance measurement block detecting existence and changes of any resistance in the read head indicative of crosstalk induced in the read head.