Certain hard disk drive systems use a magneto-resistive (MR) head for reading data on a disk. The MR head is biased with a bias voltage or a bias current. As the disk containing the data rotates adjacent to the MR head, magnetic flux from the disk varies the resistance through the MR head. The magnetic flux from the disk is a function of the data magnetically stored on the disk. The varying resistance through the MR head is indicative of the data on the disk.
A preamplifier system is used to provide the bias voltage or bias current to the MR head. A typical preamplifier system is configured to operate over a wide bias range. For example, in a current biased preamplifier system, the preamplifier system may be designed to operate with an MR head requiring a bias current in the range of 1 to 8 mA. In order to provide the desired bias range, biasing resistors in the preamplifier system are designed for the maximum bias current Imax (e.g., 8 mA) in the preamplifier's bias range. This traditional approach often results in such undesirable current noise through the MR head during operation of the preamplifier.