Digital decoding using dynamically determined tracking threshold values

Abstract

A data channel is provided that includes a digital decoder that receives a dynamically determined tracking threshold value. The tracking threshold value has a voltage amplitude used by the decoder in decoding a digital voltage signal into binary data. The digital signal is generated using an analog voltage signal that represents data read from a storage medium, such as a magnetic tape or disk. The present method is able to generate appropriate tracking threshold values even during sudden changes in the voltage amplitudes associated with the digital signal. In dynamically determining tracking threshold values, an averaging method with error recovery is employed, that is independent of the particular encoding used with the stored data. For each inputted digital voltage signal that represents a binary bit, a comparison is made between it and a current accepting value. Unless the digital voltage signal is at least equal to the accepting value, it is not used in computing a new tracking threshold value. A running average value, based on a predetermined number of the most recently accepted digital voltage signal amplitudes, is determined. An updated tracking threshold value is then determined from the current average value. A feedback loop is also utilized whereby an updated accepting value is determined to be used in accepting/rejecting further signal inputs. The error recovery is employed to decrease the accepting value if a predetermined number of consecutively received digital voltage signals are rejected.