Some Simple Self-Synchronizing Digital Data Scramblers

Two types of self-synchronizing digital data scramblers and descramblers are introduced and examined. The descramblers recover synchronization quickly after the insertion or deletion of channel bits, and they are relatively insensitive to channel errors. The scramblers act to increase the period of periodic data sequences, and the periodic channel sequences produced have approximately half as many transitions in one period as there are bits in a period. These circuits find application in common carrier systems where short-period data sequences produce high-level tones in the transmission band and, as a consequence, interchannel interference. And they have application when receiver clocks derive synchronization from transitions in the channel signal. A number of variations and modifications of the scramblers which affect their cost and size are considered. The scramblers and descramblers are similar in construction and consist of linear sequential filters with either feed-forward or feedback paths, counters, storage elements and peripheral logic. The counters, storage elements and peripheral logic monitor the channel sequence but react infrequently so that the scramblers and descramblers behave principally as linear sequential filters.