Performance evaluation of an adaptive RAM-DFE read channel

The bit error rate (BER) performance of a 54 Mbps RAM-Decision feedback equalizer (RAM-DFE) read channel for magnetic hard-disk drives is evaluated. A controlled test environment allows comparison of measured BER to the performance predicted by a model of the equalizer and channel. Implementational effects are found to degrade performance 0.6 dB in relation to theory. Measurements also show a 0.2 dB loss due to error propagation at 10/sup -8/ BER with the probability of a 30 bit burst, given a single decision error, to be less than 10/sup -5/. A simple Markov model of the error propagation process corroborates the findings. Finally, the RAM-DFE read channel is compared to a partial response maximum likelihood (PRML) detector of similar complexity on a spin-stand running with a thin-film head and media. The RAM-DFE exhibits a measured 25 fold decrease in BER over the PRML system on a wide range of densities.<>