# US 8,570,677 B2 · Implementing spin-torque oscillator sensing with enhanced integrated demodulator for hard disk drives > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,570,677 B2 - Document ID: US8570677B2 - Status: Granted - Kind: B2 - Application number: 13/316,419 - Filed: 2011-12-09 - Published: 2013-06-13 - Granted: 2013-10-29 - Earliest claimed: 2011-12-09 - Assignees: HGST Netherlands B.V. - Applicants: Patrick Mesquita Braganca; Richard Leo Galbraith; Bruce Alvin Gurney; Neil Smith; Bruce Wilson; Rehan Ahmed Zakai - Inventors: Patrick Mesquita Braganca; Richard Leo Galbraith; Bruce Alvin Gurney; Neil Smith; Bruce Wilson; Rehan Ahmed Zakai - Web page: https://patentgrep.com/patent/US8570677B2 ## CPC - H03D 3/009: {Compensating quadrature phase or amplitude imbalances} - G11B 20/10018: {analog processing for digital recording or reproduction (G11B20/10037 - G11B20/10481 take precedence)} - G11B 20/10027: {adjusting the signal strength during recording or reproduction, e.g. variable gain amplifiers (optimum power control for optical discs G11B7/125)} - G11B 2220/2516: Hard disks - H03D: DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER (masers, lasers H01S; circuits capable of acting both as modulator and demodulator H03C; details applicable to both modulators and frequency-changers H03C; demodulating pulses H03K9/00; transforming types of pulse modulation H03K11/00; coding, decoding or code conversion, in general H03M; repeater stations H04B7/14; demodulators adapted for AC systems of digital information transmission H04L27/00; synchronous demodulators adapted for colour television H04N9/66) - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A method, apparatus, and system are provided for implementing spin-torque oscillator sensing with an enhanced integrated demodulator for hard disk drives. The demodulator receives an input signal from a STO read sensor having an oscillation frequency ω related to the strength of the detected magnetic signal field. The demodulator includes a pair of mixers coupled to a quadrature reference oscillator with respective quadrature components cos(ω0t), and sin(ω0t) of the quadrature reference oscillator being mixed with a received input signal to form signals at the sum and difference frequencies, ω±ω0. Each of these mixer products is lowpass filtered by a respective a lowpass filter to remove the sum frequency components for providing a demodulator output signal that is directly proportional the STO oscillation frequency ω. The demodulator output signal is used for processing by data detection electronics. ## Claims ### Claim 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; mixing a received input signal from said STO read sensor with respective quadrature signal components cos(ω0t), and sin(ω0t) to form signals at the sum and difference frequencies, ω±ω0; lowpass filtering said signals at the sum and difference frequencies, ω±ω0 by a respective lowpass filter for providing a demodulator output signal proportional to the STO oscillation frequency ω(t); said demodulator output signal used for processing by data detection electronics; providing a respective differentiation circuit receiving a resulting modulated signal from said respective lowpass filters and providing resulting differentiated signals. ### Claim 2 (depends on 1) The method for implementing STO sensing as recited in claim 1 wherein receiving an input signal from a STO read sensor includes providing a gain limiter coupling said input signal to a pair of mixers mixing said received input signal with respective quadrature signal components cos(ω0t), and sin(ω0t). ### Claim 3 (depends on 2) The method for implementing STO sensing as recited in claim 2 includes providing a quadrature reference oscillator including a frequency ω0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field. ### Claim 4 (depends on 3) The method for implementing STO sensing as recited in claim 3 wherein providing said quadrature reference oscillator includes implementing said quadrature reference oscillator with a single oscillator with split outputs separated by a 90-degree phase shifter. ### Claim 5 (depends on 1) The method for implementing STO sensing as recited in claim 1 includes providing a second pair of mixers coupled to said respective lowpass filters and said respective differentiation circuits, for mixing said resulting modulated signal from said respective lowpass filters and said resulting differentiated signals from said respective differentiation circuits. ### Claim 6 (depends on 5) The method for implementing STO sensing as recited in claim 5 includes providing a differential amplifier coupled to an output of said second pair of mixers, said differential amplifier having a unity gain, forming a signal represented by g(t). ### Claim 7 (depends on 6) The method for implementing STO sensing as recited in claim 6 includes providing a second lowpass filter coupled to said differential amplifier and lowpass filtering said signal g(t), providing said demodulator output signal. ### Claim 8 (depends on 1) The method for implementing STO sensing as recited in claim 1 includes providing said respective lowpass filters to accommodate a maximum frequency shift of said STO read sensor oscillation frequency ω(t) responsive to maximum magnetic field. ### Claim 9 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 having an oscillation frequency ω(t); a demodulator including a pair of mixers coupled to a quadrature reference oscillator mixing a received input signal from said STO read sensor with respective quadrature signal components cos(ω0t), and sin(ω0t) to form signals at the sum and difference frequencies, ω±ω0; and a respective lowpass filter receiving and lowpass filtering mixer signals to remove the sum frequency components for providing a demodulator output signal proportional the STO oscillation frequency ω(t), said demodulator output signal being used for processing by data detection electronics; and a respective differentiation circuit receiving a resulting modulated signal from said respective lowpass filters and providing resulting differentiated signals. ### Claim 10 (depends on 9) The apparatus for implementing data detection as recited in claim 9 wherein said quadrature reference oscillator includes a single oscillator with split outputs separated by a 90-degree phase shifter. ### Claim 11 (depends on 9) The apparatus for implementing data detection as recited in claim 9 wherein said quadrature reference oscillator includes a frequency ω0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field. ### Claim 12 (depends on 9) The apparatus for implementing data detection as recited in claim 9 includes a second pair of mixers coupled to said respective lowpass filters and said respective differentiation circuits, for mixing said resulting modulated signal from said respective lowpass filters and said resulting differentiated signals from said respective differentiation circuits. ### Claim 13 (depends on 12) The apparatus for implementing data detection as recited in claim 12 includes a differential amplifier coupled to an output of said second pair of mixers, said differential amplifier having a unity gain to form a signal g(t). ### Claim 14 (depends on 13) The apparatus for implementing data detection as recited in claim 13 includes a second lowpass filter coupled to said differential amplifier and lowpass filtering said signal g(t), providing said demodulator output signal. ### Claim 15 (depends on 9) The apparatus for implementing data detection as recited in claim 9 includes a gain limiter coupling said input signal to said pair of mixers. ### Claim 16 A system for implementing data detection with spin-torque oscillator (STO) sensing for hard disk drives comprising: a media generating 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 having an oscillation frequency ω(t); a demodulator including a pair of mixers coupled to a quadrature reference oscillator mixing a received input signal from said STO read sensor with respective quadrature signal components cos(ω0t), and sin(ω0t) to form signals at the sum and difference frequencies, ω±ω0; and a respective lowpass filter receiving and lowpass filtering mixer signals to remove the sum frequency components for providing a demodulator output signal proportional the STO oscillation frequency ω(t), said demodulator output signal being used for processing by data detection electronics; a respective differentiation circuit receiving a resulting modulated signal from said respective lowpass filters and providing resulting differentiated signals; and a second pair of mixers coupled to said respective lowpass filters and said respective differentiation circuits, for mixing said resulting modulated signal from said respective lowpass filters and said resulting differentiated signals from said respective differentiation circuits. ### Claim 17 (depends on 16) The system for implementing data detection as recited in claim 16 wherein said quadrature reference oscillator includes a frequency ω0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field.