Patent ID: 8351155

Claim:
A perpendicular magnetic recording disk drive: a disk having a perpendicular magnetic recording layer; a write head for magnetizing regions of the recording layer comprising a main pole; a main electrically conductive coil coupled to the main pole for generating magnetic flux in the main pole in the presence of electrical write current; and a spin torque oscillator (STO) having first and second electrodes and a free ferromagnetic layer between the electrodes, the free layer having a magnetization free to rotate in the presence of an electrical current between the electrodes, the rotation of the free layer magnetization generating an auxiliary magnetic flux directed to the main pole at an angle to the main pole greater than 15 degrees and less than or equal to 90 degrees; a write driver capable of supplying write current in two directions to the main coil; a read head for detecting magnetized regions in the recording layer and generating a readback signal; a read amplifier for amplifying the readback signal from the read head; an integrated lead suspension (ILS) having electrically conductive traces connecting the write driver to the write head and electrically conductive traces connecting the read amplifier to the read head; STO control circuitry for supplying direct electrical current to the STO electrodes when write current is supplied to the main coil, the STO circuitry being connected to the STO via traces connecting the write driver to the write head; and a pair of matched resistors between the write driver and the write head; and wherein the STO control circuitry includes a low-pass filter coupled to the common-mode through the resistors, a voltage source, and a comparator for comparing the output of the low-pass filter to the voltage source.