Modified coherent PN-code tracking delay-locked loop
Andreas Wilde · 2002
In spread spectrum systems PN-code tracking is a crucial performance aspect. The delay-locked loop (DLL) is an appropriate device to guarantee fine synchronisation. In this paper, a modification of the coherent DLL with an early-late spacing of 2/spl Delta/ is proposed. In the design of a DLL there is a tradeoff between tracking jitter and tracking range. The 2/spl Delta/-loop has the largest tracking range, but a poor tracking jitter performance. However, the jitter performance is improved by reducing the noise power in the loop. This is achieved by selecting the strongest DLL branch, i.e. early or late branch. This modifies the coherent DLL detector S-curve only slightly while reducing the noise power by a factor of 3 dB. A performance analysis is done for the coherent 2/spl Delta/-loop in a Gaussian noise environment and the results are compared to the conventional coherent 1/spl Delta/- and 2/spl Delta/-loops.