MAGNETIC RECORDING CHANNEL FRONT-ENDS

Readback front-end electronics for both inductive and MR-recording heads are investigated. For inductive front-ends it is shown that the channel bandwidth is determined by the transfer of the induced head voltage to the front-end input terminals. The parameters limiting this bandwidth are calculated. A noise analysis shows that the S/N ratio can be optimized and gives the parameter values for which this happens. The effect of noise matching of the head to the front-end is demonstrated. For MR front-ends the principles of auto bias and relative resistance sensing are presented. Front-end configurations producing voltage biasing and current biasing are discussed. Finally, two examples of signal conditioning in MR front-ends are given: an on-the-chip equalizer compensating the frequency roll-off introduced by the head cable inductance, and a signal-adaptive circuit for removing thermal asperities.