Decision feedback equalization of the dc null in high-density digital magnetic recording

The dc null in a digital magnetic recording channel is equalized in a novel way which allows recovery of direct recorded NRZ waveforms with no coding constraints. The technique involves decision feedback equalization which can be implemented with simple filters. Feedback power is determined by the choice of and can be optimized independently of the fact of equalization. Measurements on a commercial helical-scan video transport indicate that the harmful effects of a dc null can be greatly reduced; specifically the error rate (excluding dropouts) on a 1023-bit 20-Mbit/sec pseudorandom pattern was reduced from 3 × 10^-5to below 10^-8.