Abstract: A fly height controller circuit for a disk drive head having a resistive heater is disclosed. The fly height controller includes an error amplifier that controls a variable current source driving the resistive heater. The error amplifier compares a desired heater power signal with a feedback power signal that is generated by a multiplier. The multiplier receives a signal corresponding to the resistive heater current, for example as generated by a second variable current source also controlled by the error amplifier, and a signal corresponding to a voltage across the resistive heater. A first differential amplifier develops a differential voltage corresponding to the heater voltage. A second differential amplifier is biased by the resistive heater current signal, and receives the differential voltage form the first differential amplifier. A differential current generated by the second differential amplifier produces the feedback power signal as an output voltage.

Abstract: A write head drive circuit for a magnetic data storage device is configured to drive a write head with a write head degaussing current that is applied at the end of a write cycle. The write head degaussing current is an alternating current waveform with a programmable number of current pulses with decreasing amplitude and a frequency controlled by a CMOS ring oscillator. The CMOS ring oscillator includes switchable feedback paths to control its frequency. A programmable timer terminates the write head degaussing current after an interval of time dependent on signals that indicate the programmable number of current pulses and the frequency of the CMOS oscillator.