An all-digital realization of a baseband DLL implemented as a dynamical state estimator

The delay-locked-loop (DLL) is a device that automatically adjusts a local delay estimate to the time delay between two versions of an incoming signal. It has been shown that, in the sense of local variance, this device performs equally as well as the maximum-likelihood estimator, whereas the implementation cost can be reduced considerably. Several publications describe digital or hybrid implementations of such a device for the tracking of PN-codes, for example. This paper, however, deals with a baseband type of the DLL, which was developed for noncontact range, speed, and acceleration measurement by means of two signals generated by spatially separated infrared sensor. To obtain an unbiased estimate under meaningful signal model assumptions, a dynamical state estimator was implemented for the above quantities. The state model is linear, whereas the measurement equation is highly nonlinear. To perform this nonlinear output operation, a novel numerical controlled oscillator (NCO) was developed that works with normalized exponential representation of the control number that allows us to match the loop to a wide range of the sampling rate via gain scheduling. An all-digital implementation of the estimator and results of a field test are presented.