Magneto-resistive head pre-amplifying circuit for avoiding output

Abstract

A circuit is disclosed for pre-amplifying signals from an MR sensor in a disk drive without producing output voltage transients as the MR head changes its operational mode. In one preferred embodiment, the circuit includes a bias current source, an input stage, and a voltage clamp across the inputs of the OTA of the input stage. The input stage remains active in all modes of the MR head to avoid transients generated by the thermal responses of the MR sensor. In a second embodiment, the circuit allows the current from a first current source to bypass the input stage and flows directly to the MR sensor in write or idle mode. The bias current remains generally constant in all modes, thus avoiding output transients. In the third embodiment, upon switching to read state, the MR sensor is biased with an additional current source to quickly heat up the sensor. Upon reaching the normal read-mode temperature, the additional current is cut off and the sensor is again biased with only the first current source, thus avoiding voltage transients at the output of the circuit.