An Analysis of Inherent Distortion in Asynchronous Frequency-Shift Modulators

A large p a r t of present-day d a t a c o m m u n i c a t i o n s systems utilize bin a r y frequency-shift channels for transmission. In such systems, particularly in t h e wideband systems (i.e., s y s t e m s in which t h e bit r a t e is n o t small compared to the carrier frequency), t h e problem of " j i t t e r " is i m p o r t a n t . J i t t e r is t h e error in the reproduction of the exact time of transition between m a r k i n g a n d spacing signals at the receiver o u t p u t . T h i s problem is indicated in Fig. 1, in which it is assumed t h a t t h e indicated data-source waveform is jitter-free a n d is t r a n s m i t t e d repetitively. T h e received waveforms arc shown overlapping one a n o t h e r . N o t e t h a t , in addition to a usually harmless transmission delay, t h e receiver transitions do not all occur at t h e same relative time, b u t are instead distributed a b o u t t h e correct transition. T h e measure of j i t t e r which will be used in this p a p e r will be t h e m a x i m u m time error which m a y occur in the system, denoted by r