An improved delay lock loop for use in ranging and data modulated spread-spectrum systems

Switching the phase of the discriminator characteristics of a delay lock loop (DLL) has previously been shown to improve the maximum search rate possible when the DLL is used to acquire initial synchronisation between two maximal length pseudonoise sequences. However, the theoretical analysis in this earlier work was found to be over optimistic when compared with the experimental results, because the analysis failed to take into account the effects of switching transients. The paper shows how the loop may be modified to remove switching transients, and hence achieve results which are as good as the original predictions. The paper shows the effect of the maximum initial search rate on the pull-in time of both standard and switched DLLs, and it is seen that increasing the epoch search rate can worsen the pull-in time of the loop near the maximum allowable value. The paper also shows how the switched DLL may be applied, in a cost effective way, to the case of a spread-spectrum system with data modulation using a form of data feedback which enables the DLL to acquire lock with no loss of performance.