Implementing spin-torque oscillator sensing with enhanced integrated demodulator for hard disk drives
View Patent ↗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(ω 0 t), and sin(ω 0 t) of the quadrature reference oscillator being mixed with a received input signal to form signals at the sum and difference frequencies, ω±ω 0 . 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.
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(ω 0 t), and sin(ω 0 t) to form signals at the sum and difference frequencies, ω±ω 0 ;
lowpass filtering said signals at the sum and difference frequencies, ω±ω 0 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.
2. 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(ω 0 t), and sin(ω 0 t).
3. The method for implementing STO sensing as recited in claim 2 includes providing a quadrature reference oscillator including a frequency ω 0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field.
4. 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.
5. 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.
6. 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).
7. 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.
8. 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.
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(ω 0 t), and sin(ω 0 t) to form signals at the sum and difference frequencies, ω±ω 0 ; 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.
10. 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.
11. The apparatus for implementing data detection as recited in claim 9 wherein said quadrature reference oscillator includes a frequency ω 0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field.
12. 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.
13. 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).
14. 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.
15. The apparatus for implementing data detection as recited in claim 9 includes a gain limiter coupling said input signal to said pair of mixers.
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(ω 0 t), and sin(ω 0 t) to form signals at the sum and difference frequencies, ω±ω 0 ; 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.
17. The system for implementing data detection as recited in claim 16 wherein said quadrature reference oscillator includes a frequency ω 0 approximately equal to a frequency of the STO read sensor in a quiescent bias state in the absence of an external signal field.