Method and apparatus for removing data stream variations

Abstract

The specification discloses means for correcting timing variations present in a data stream emanating from a data storage device such as a magnetic tape drive or the like before the data stream is applied to the data separator or other such input device of a computer. This is accomplished by remodulating the time-varying bits in the data stream in a manner which reduces or eliminates the undesired timing variations. Basically, the system utilizes frequency-modulation techniques to in effect remodulate the raw data stream. The application discloses, as one preferred embodiment, a pulse-width modulator which receives the error signal output of a phase-locked loop network, the input of the pulse-width modulator being coupled to the incoming raw data stream. The primary output of the phase-locked loop circuit is coupled to the input of the pulse-width modulator, and the output of the pulse-width modulator is coupled to the input of a pulse generator so as to produce output pulses of substantially uniform width which occur in synchronism with output pulses of the pulse-width modulator and thus constitute in effect a remodulated version of the raw data stream, in which the undesired timing variations have been removed or reduced by an acceptable level.