Head Signal Quality Distributions

How do you determine the quality of your PRML signal? SAM histograms provide a direct indication of how much margin you have, what the noise contribution to signal quality is, and whether there are anomalous events. Shown below is a SAM histogram of a noisy PR4 signal (top) with distinct non-noise anomalies indicated by the histogram (bottom). The center of the display indicates a 0 SAM value.

Rapidly Locate PRML Signal Quality Problems

If you do not know the exact location of a PRML error, or if you want to locate signal areas with poorest margins from a PRML channel viewpoint, use the DDA 260’s powerful channel tools. Simply turn a knob, and the DDA 260 will display your head signal in order of signal locations with worst SAM. Also displayed will be the corresponding SAM value for each location.

Head Signal Quality Line Graphs

Easily observe how head-signal quality varies over a PRML signal. Shown below is a PRML head signal (top) and a trace of how the head signal quality (SAM) varies from nominal (bottom). The signal spike shown is a clear indication of a PRML signal quality problem and its location.

PES Runout Analysis

See the values for the Position Error Signal (PES) runout contributors for each wedge around a track. Values provided include Repetitive Runout, Non-Repetitive Runout, and Instantaneous Runout.