Reproducing circuit for magneto-resistive head having an initial amplifying stage, a differential amplifying stage, and means for controlling the time of operation thereof

摘要

A recording/reproducing apparatus for a magneto-resistive (MR) head having a playback amplifier, including a capacitor for a dc feedback low-pass filter for dc feedback to an initial-stage transistor, and a differential amplifier (gm amplifier), and a switching device for the gm amplifier and for the initial-stage amplifier operable at the time of recording/playback switching. The timing of the switching device is deviated for shortening the switching time interval. To this end, an output of the initial-stage transistor of a playback amplifier for a MR head is compared to reference voltage Vref by a gm amplifier and the low-pass filter is constituted by transconductance gm of the gm amplifier and the capacitance of the capacitor, with the dc output of the gm amplifier being fed back to the base of the initial-stage amplifier. The delay in switching time by the charging of the capacitor caused by the difference in the rise time of the initial-stage transistor and the gm amplifier is deviated by the control signal from a control circuit to control the initial-stage transistor and the gm amplifier.