Discrete time control loop for the magnetic tape channel

Abstract

The Discrete Time Control Loop (DTCL) performs channel timing without requiring an active PLO. It can be expressed as an algorithm, implementable in hardware or software. The algorithm is illustrated on a simple example, and its transfer function derived. Its response to a velocity step and to transition shifts are examined. The DTCL provides timing to the 16-channel IBM 3590 tape system. Phase correction is performed individually per channel, while frequency correction is done globally by averaging all frequencies. Timing is still available if a dropout occurs in any channel.