ZERO-CROSSING INTERPOLATOR TO REDUCE ISOCHRONOUS DISTORTION IN A DIGITAL FSK MODEM

摘要

In a digital data communication receiver, an apparatus for estimating the time of zero-crossing between successive samples of a continuous frequency shift keyed (FSK) or like zero-crossing signal in a manner more accurate than is provided by the basic sampling clock. The apparatus includes means for sensing a change in sign relative to successive samples of the signal and means responsive to the sensed sign change to interpolate between the values of the respective samples for indicating more accurately the time of occurrence of the zero-crossing prior to the second sample, thereby demodulating the continuous signal.