Fast charge and thermal asperity compensation circuit

Abstract

An MR head circuit including a differential amplifier, means for applying a dc bias to the head, a capacitor mounted in parallel to the head to eliminate the dc voltage offset, and a feedback loop configured for evaluating the differential voltage and for controlling the current in portions of the amplifier to rapidly charge the capacitor upon circuit activation. The feedback loop also includes a thermal asperity compensator configured for producing a given signal, both upon activation of the circuit and when the magnitude of the voltage differential exceeds a given value, and the feedback loop includes means responsive to the given signal for altering select current paths of the feedback loop to thereby produce elevated charging currents in the differential amplifier during initial activation, and to increase the ac gain of the feedback loop at other times so as to raise the lower corner frequency of the differential amplifier to filter out the relatively low frequency of a thermal asperity waveform. The feedback loop includes current paths for developing difference currents representing the differential output voltage, and each path is coupled to the differential amplifier for controlling it, and the current paths include a shunt transistor operative for altering the resistance of the current paths and the ac gain of the current network responsive to the given signal.