On the performance of a low complexity baseband 2nd order delay locked loop incorporating a non-linear NCO

We present a fully digital delay locked loop (DLL) which incorporates low complexity complex-signal phase detector and non-linear NCO components. The NCO is based on a pulse position modulation (PPM) method which is implemented using a fixed time-precision interpolator. Unlike the conventional DLL which uses a linear VCO, the NCO used here is highly non-linear. The DLL structure is described and the performance of the MA-ABS phase detector is presented. The closed loop performance is analysed for the case of a second order loop filter and the results of digital simulations are presented