Current source for a magnetoresistive head with variability and

Abstract

A low noise current source circuit is disclosed for biasing a magnetoresistive (MR) read head. The current source comprises a field-effect transistor (FET) cascoded to a second transistor which, in turn, is coupled to the MR element. A filter device including a capacitor is coupled across the gate-source junction of the FET, and a sensing device, such as a resistor, is coupled to the gate of the FET for detecting current flowing into said capacitor. Boost circuitry, coupled to the sensing device, boosts the charge/discharge rate of the filter capacitor when the voltage of the sensing device exceeds a certain threshold.