Circuitry for correction of thermal transients in the analog signal from

Abstract

Thermal transient signal detection/correction circuitry corrects for errors caused by actual thermal asperities and baseline wander in the analog signal from a magnetoresistive (MR) sensor, such as an MR read head in a magnetic recording disk drive. In a disk drive with an MR head the detection/correction circuitry is located between the MR head signal amplifier and the data readback channel so that the thermal transients are corrected in the analog data signal prior to processing of the analog data signal into digital data. A detection circuit receives the analog data signal from the MR head, low-pass filters the signal and generates a thermal asperity event signal if the filtered signal exceeds a predetermined threshold. A correction circuit also receives the analog data signal from the MR head and includes a high-pass filter whose pole frequency is controlled by the thermal asperity event signal from the detection circuit. In the event of a detected thermal transient the pole frequency is quickly raised to bring the baseline of the analog data signal back to normal, which turns off the output of the detection circuit. The correction circuit then lowers the pole frequency gradually. The thermal transient detection/correction circuit thus quickly restores the baseline of the analog data signal to zero, quickly enables data to be read after the onset of a thermal transient and eliminates undershoot in the analog data signal due to the slowly changing tail of the thermal transient.