1. Field of the Invention
The present invention relates to a magnetic recording system, and more specifically, to asymmetry correction for a magnetic recording read channel with magneto-resistive (MR) read heads.
2. Description of the Related Art
It is known to use MR read heads to read signals in magnetic media. The MR head reads the stored signals by converting a magnetic field into resistance. Because of nonlinear effects, the MR read head introduces asymmetry into magnetic recording channels.
FIG. 1 is a block diagram of a conventional magnetic recording channel 100 with an MR head, and resulting asymmetry. Only parts relevant to asymmetry correction are shown. In FIG. 1, an H(jw) block 101 represents the head/media response. A block 102 for x+px2 models the MR head asymmetry. The output of the block 102 passes through an equalizer 120 including a filter, such as a CTF (continuous-time filter) 103; in one embodiment, through an ADC (analog-to-digital converter) or sampler 104; and an output adjustment block, such as a FIR (finite impulse response) block 105.
MR read head asymmetry degrades performance. Since the MR read head asymmetry, modeled in general by a function x+px2, is nonlinear, it needs to be corrected nonlinearly. An accepted practice is to use another nonlinear function to counteract the MR read head asymmetry at a position as close to the origin of the asymmetry as possible.
One conventional way of providing the additional nonlinear function is to introduce a second-order nonlinear function −qy2 to offset the asymmetry of the MR read head. The scheme for this MR read head asymmetry correction approach is shown in the magnetic recording channel 100′ depicted in FIG. 2, in which the second-order correction is provided in block 110, which also shows an equalizer 120′ through which the output of that block passes. However, a second-order function is not easy to implement in analog circuitry.
Therefore, it would be advantageous to provide an easier-to-implement method and apparatus for MR read head asymmetry correction.