APPARATUS AND METHOD FOR AN ERROR MINIMIZING PHASE LOCKED LOOP

A method of estimating a period and a time delay, or phase, of an input signal. A plurality of transition times {tilde over (t)}i are received, each transition time {tilde over (t)}i having a weight &agr;{tilde over (&ggr;)}i comprising a forgetting factor &agr; and a weighting factor {tilde over (&ggr;)}i. Upon receiving an Nth transition time to and determining an Nth weighting factor &ggr;0, maximum likelihood estimates {circumflex over (T)} and {circumflex over (t)}&phgr; of the period and the time delay, respectively, are calculated. The estimates are computed recursively, with {circumflex over (T)} depending upon &agr;, &ggr;0, t0, and a preceding maximum likelihood estimate {circumflex over (T)} of the period. The value of {circumflex over (t)}&phgr; depends upon &agr;, &ggr;0, and t0. The estimates {circumflex over (T)} and {circumflex over (t)}&phgr; also depend on sums SN−1(n)=&Sgr;i=−(N−2)0in&agr;−i{circumflex over (&ggr;)}i. After the estimates {circumflex over (T)} and {circumflex over (t)}&phgr; are computed, the sums are updated in anticipation of the next transition time. The method is preferably implemented electronically, resulting in a digital phase locked loop. The weighting factors allow the digital phase locked loop to lock onto a signal having absent transitions.