Vector tracking filter

Abstract

A new filter that may be employed in timing recovery circuits, and automatic gain control circuits, employs a so-called vector tracking filter (VTF). The VTF includes a complex filter with a time constant so long that it might be considered a leaky integrator. In operation, the VTF builds up an average vector (timing (gain) estimate vector) having a direction that is the average of the estimated timing (gain) error, which is stored in the VTF. When the VTF is employed in an automatic gain control arrangement, the vector becomes a scalor and only the amplitude is tracked. When an arbitrary timing (gain) correction is made, to the incoming signal, this causes a rotation of the timing (gain) estimate vector. In order to track this rotation, a comparable rotation is made to the stored timing (gain) estimate vector. This allows the stored timing (gain) estimate vector to build up, and at any time the stored timing (gain) estimate vector will be the same as if the current incoming phase had been constant for all previous time. Consequently, it is possible to use a very long time constant in the VTF for long-term steady timing (gain) and at the same time acquire timing (gain) fast. In one example, the length of the vector stored in the VTF is allowed to build up until it reaches the mean value of the incoming timing (gain) estimate.