Low noise voltage-biasing amplifier for magnetoresistive element

A circuit for concurrently producing low noise electrical output signals which are amplified representations of signals produced by a magnetoresistive (MR) element (11) and protecting said element from electrical short circuits which can occur between said element and its environment, said circuit comprising:

• a first feedback loop comprising a forward gain path and a reverse gain path;
• said forward gain path including means for applying a bias voltage across the MR element, and means for converting an input signal current representing the bias voltage divided by dRh into an output signal voltage represented by dRh/RhRh, where said RhRh is the square of the time-averaged resistance of the MR element and said dRh is the magnetic-signal-induced change in the resistance of the MR element;
• and
• said reverse gain path including an operational transconductance amplifier (OTA) (g0) with a dominant low-frequency pole (P0) for biasing the forward gain path with a bias current (Ja) which minimizes dc offset error of the forward gain path (at V.sub.jout ) and concurrently biases the MR element with the bias voltage.

A magnetic recording disk file comprising:

• a rotatable magnetic recording disk;
• a magnetoresistive (MR) element supported proximate the disk for sensing magneto transitions on the disk;
• and
• a circuit including the MR element for producing low noise electrical output signals which are amplified representations of signals produced by the MR element, said circuit further including:
• an input amplifier;
• and
• means, including a first feedback loop, providing a common bias current both for biasing the MR element with a bias voltage and for concurrently biasing the input amplifier, said amplifier being operative to amplify a signal current from the MR element to produce a circuit output signal corresponding to dRh/RhRh and having minimal differential dc output offset error, where said RhRh is the square of the time-averaged resistance of the MR element and said dRh is the magnetic-signal-induced change in the resistance of the MR element.