Direction-constrained ternary codes using peak and polarity detection

Abstract

A class of ternary square wave signals is detectable by peak polarity detection alone without need for amplitude discrimination. The ternary codes are used to increase data density recording at the same clock rate as binary codes. This is satisfied by selective direction-constrained run length limited (RLL) signals. The direction constraint is that the half-step transitions can only occur in pairs of the same polarity. Alternate half-step pairs of opposite polarity are forbidden. This avoids the need for amplitude discrimination. The RLL (d,k) constraint includes 'd' number of clock times when a transition is forbidden and 'k>d' clock times within which consecutive transitions must occur. The latter determines a minimum frequency for clocking purposes. This eases peak shift detection.