STACK FILTER PHASE-LOCK LOOPS

The basic design of a general purpose digital phase lock loop is impro ved upon by incorporating a stack filter into the feedback path of the loop. The addition of a stack filter provides enhanced performance in the presence of impulsive noise while providing the same steady-state performance of a conventional digital phase lock loop. Both first- an d second-order loops benefit from the addition of stack filters. The p articular case of using a median filter is examined in detail. In addi tion, a linear regression model is used in conjunction with the absolu te error criterion to provide robust estimates of phase and frequency. The resulting loop structure incorporates median and weighted median filters in its feedback path.