Implementing spin-torque oscillator sensing with enhanced demodulator for hard disk drives

• US 8,654,465 B2
• Filed: 12/09/2011
• Issued: 02/18/2014
• Est. Priority Date: 12/09/2011
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: HGST Netherlands B.V. (Western Digital Corporation)
• Inventors: Braganca, Patrick Mesquita, Galbraith, Richard Leo, Gurney, Bruce Alvin, Smith, Neil, Wilson, Bruce, Zakai, Rehan Ahmed
• Primary Examiner(s): HOLDER, REGINA NEAL
• Application Number:
  US13/316,342
• Publication Number:
  US 20130148223A1
• Time in Patent Office: 802 Days
• Field of Search: None
• US Class Current: 360/30
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/1284 Spin resolved measurements; Influencing spins during measurements, e.g. in spintronics devices G01R33/093 takes precedence; semiconductor devices using spin polarized carriers H01L29/66984
• CPC Class Codes: G11B 20/10018 analog processing for digital recording or reproduction G11B20/10037 - G11B20/10481 take precedence
• CPC Class Codes: G11B 2005/0016 of magnetoresistive transducers
• CPC Class Codes: G11B 2220/2516 Hard disks
• CPC Class Codes: G11B 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: H03B 15/006 using spin transfer effects or giant magnetoresistance

Abstract

A method, apparatus, and system are provided for implementing spin-torque oscillator (STO) sensing with a demodulator for hard disk drives. The demodulator measures an instantaneous phase of the readback signal from a STO sensor and converts the readback signal into a signal that is proportional to the magnetic field affecting the STO frequency during a bit time. The converted signal is used for processing by conventional data detection electronics.

Claims

1. A method for implementing data detection with spin-torque oscillator (STO) sensing with a demodulator for hard disk drives comprising:

receiving an input signal from a STO read sensor having an oscillation frequency ω

(t) related to magnetic field varying in time in response to a varying applied magnetic field;

providing a mixer for mixing said readback signal with a quadrature reference frequency signal producing a complex baseband readback signal;

said quadrature reference frequency signal having a frequency approximately equal to said STO read sensor in a quiescent bias state;

providing a phase detector for measuring an instantaneous phase of said complex baseband a readback signal from said STO read sensor; and

providing a finite difference function coupled to said phase detector converting said processed readback signal into a converted signal proportional to the magnetic field affecting frequency of said STO read sensor during a bit time;

said converted signal being used for processing by data detection electronics.

2. The method for implementing STO sensing as recited in claim 1 includes mixing said readback signal with said quadrature reference frequency signal including quadrature reference frequency components represented by cos(ω

_ct), and i.sin(ω

_ct).

3. The method for implementing STO sensing as recited in claim 1 includes providing a mixer for mixing said readback signal with said quadrature reference frequency signal being positioned proximate to said STO read sensor.

4. The method for implementing STO sensing as recited in claim 3 includes providing a lowpass filter coupled to said mixer, said mixer producing said complex baseband signal comprising in-phase and quadrature components, and said lowpass filter lowpass filtering said complex baseband signal.

5. The method for implementing STO sensing as recited in claim 4 includes providing said phase detector coupled to said lowpass filter.

6. The method for implementing STO sensing as recited in claim 1 wherein converting said readback signal into said converted signal includes providing a lowpass filter coupled to said phase detector and lowpass filtering a resulting signal from said phase detector.

7. The method for implementing STO sensing as recited in claim 6 includes providing said finite difference function coupled to said lowpass filter for yielding said converted signal proportional to captured flux affecting said STO frequency during said bit time.

8. An apparatus for implementing data detection with spin-torque oscillator (STO) sensing for hard disk drives comprising:

a spin-torque oscillator (STO) read sensor sensing a signal magnetic field and producing a readback signal;

a mixer coupled to a quadrature reference oscillator mixing said readback signal from said STO read sensor with a quadrature reference frequency signal producing a complex baseband readback signal;

said quadrature reference frequency signal having a frequency approximately equal to said STO read sensor in a quiescent bias state;

a lowpass filter receiving and lowpass filtering said complex baseband readback signal;

a frequency modulation (FM) demodulator including

a phase detector coupled to said lowpass filter measuring an instantaneous phase of said filtered complex baseband readback signal;

a second lowpass filter coupled to said phase detector and lowpass filtering a resulting signal from said phase detector; and

a finite difference function coupled to said second lowpass filter converting the filtered complex baseband readback signal into a signal that is proportional to captured flux affecting the STO frequency during a bit time;

the converted signal being used for processing by data detection electronics.

9. The apparatus for implementing data detection as recited in claim 8 includes said mixer mixing said readback signal from said STO read sensor with a quadrature reference frequency signal including quadrature reference frequency components represented by cos(ω

_ct), and i.sin(ω

_ct).

10. The apparatus for implementing data detection as recited in claim 8 includes said mixer producing said complex baseband signal comprising in-phase and quadrature components, and said mixer being positioned proximate to said STO read sensor.

11. The apparatus for implementing data detection as recited in claim 8 includes an amplifier coupled to said STO read sensor amplifying said readback signal.

12. The apparatus for implementing data detection as recited in claim 11 wherein said mixer receiving said amplified readback signal from said amplifier.

13. A system for implementing data detection with spin-torque oscillator (STO) sensing for hard disk drives comprising:

a magnetic signal having an amplitude determined by media field strength;

a spin-torque oscillator (STO) read sensor sensing said magnetic signal generated by said media and producing a readback signal;

a mixer coupled to a quadrature reference oscillator mixing said readback signal from said STO read sensor with a quadrature reference frequency signal producing a complex baseband readback signal;

said quadrature reference frequency signal having a frequency approximately equal to said STO read sensor in a quiescent bias state;

a lowpass filter receiving and lowpass filtering said complex baseband readback signal;

a frequency modulation (FM) demodulator including

a phase detector coupled to said lowpass filter measuring an instantaneous phase of said filtered complex baseband readback signal;

a second lowpass filter coupled to said phase detector and lowpass filtering a resulting signal from said phase detector; and

a finite difference function coupled to said second lowpass filter converting the filtered complex baseband readback signal into a signal that is proportional to captured flux affecting the STO frequency during a bit time;

the converted signal being used for processing by data detection electronics.

14. The system for implementing data detection as recited in claim 13 includes said mixer mixing said readback signal from said STO read sensor with said quadrature reference frequency signal including quadrature reference frequency components represented by cos(ω

_ct), and i.sin(ω

_ct).