Viterbi Detection of Class IV Partial Response on a Magnetic Recording Channel

The application of Viterbi detection to Class IV partial response on a magnetic recording channel is discussed. The theoretical performance is analyzed in the presence of noise correlation and quantizing errors. A simplified algorithm is described which was implemented on a transverse-scan magnetic tape recorder operating at a linear density of 1800 bits/mm and a transfer rate of 120 Mbits/s. Following an initial 5 bit analog-to-digital conversion of the ternary waveform, the Viterbi detector is implemented entirely in high-speed digital emitter-coupled logic. An advantage of approximately 1.5 dB in effective signal-to-noise ratio is gained over a simple level detector, a result which agrees well with the theoretical development.