The PRML Technic Research And Application In Magnetic Recording Systems

Hard Disk Drive (HDD) is one of the most widely used storage accessory, which uses magnetic recording to store data. The important technique used in magnetic recording is PRML (Partial Response Maximum Likelihood). This technique first applied in industry for HDD in January of year 1990.Partial response is a digital signal process method which can do a good job to reduce inter-symbol inference. It equalizes the signal to a certain target to reduce ISI and hence reduce bit error rate (BER) to improve channel performance. Maximum likelihood uses Viterbi algorithm to detect the data.First and second generation PRML systems operate on PR-IV target-equalized waveforms. Longer targets, such as EPR-IV and E 2 PR?IV, tend to better match the natural channel spectral characteristics, meaning less signal equalization is required, and thus a smaller noise enhancement occurs. Higher performance is thus offered by systems operating on these more complex targets, as they offer a higher equalized signal-to-noise (SNR). However, because the detector must distinguish more levels within a more complex target waveform, its sensitivities to gain- and timing-errors are also higher.Base on the increase of recording density and the rapid improved of process speed, we need a new architecture of PRML channel to gain better performance. This dissertation gives a solution of this useful architecture, which includes VGA, CTF, FIR, and ADC these functional blocks.At the end of this document, perpendicular recording is introduced. This technique has increased the capacity of HDD tremendously. Comparing some characteristics between longitudinal and perpendicular recording, most of the current read channel can be compatible.