METHOD AND APPARATUS FOR ENCODING AND DECODING AN NRZI DIGITAL SIGNAL WITH LOW DC COMPONENT AND MINIMUM LOW FREQUENCY COMPONENTS

摘要

A converted digital signal is provided in an NRZI (non-return to zero, inverted) code with a DC component of zero and with a maximum predetermined number of bits between level transitions in the signal. The base digital signal is divided into m-bit base words, each of which is then converted into an n bit converted code to form a converted digital signal suitable for recording. The n-bit converted code includes a plurality of primary combinations having a DC component substantially equal to zero when NRZI-coded and a plurality of secondary combinations having a DC component with an absolute value of two when NRZI-coded. A variance of DC charge of the primary combination when NRZI-coded and a polarity of DC component of the secondary combination when NRZI-coded are altered in response to DC charge of the preceding converted digital signal.