CARRIER RECOVERY SYSTEM

A digital carrier recovery system includes at least two modes of operatio n, namely, an acquisition mode and a tracking mode. The bandwidth of the carrie r recovery loop filter is different for the acquisition mode and the tracking mode. In the acquisition mode, the digital phase-locked loop seeks and locks to the long term frequency offset of the received carrier signal. In the tracking mode, the digital phase-locked loop tracks the instantaneous variations in the carrier phase. Switching between the acquisition mode and the tracking mode is realized digitally, and includ es programmable hysteresis, resulting in optimal performance in the presence of signals having high levels of phase noise (jitter). More specifically, the carrier recovery loop filter "locks" to the pilot signal of an incoming signal, e.g., a vestigial side band (VSB) video signal, by employing a so-called digital vector tracking phase-locked loop that demodulates the VSB signal. The digital vector tracking phase-locked loop includes a complex filter, i. e., a so-called vector tracking filter, that very quickly locks to the pilot signal of the passband VSB signal and once locked to the pilot signal, switches to the tracking mode that provides significantly better tracking of phase noise. Th e demodulation is achieved by employing a complex multiplication of the incomi ng signal with a complex exponential sequence to obtain an in-phase (I-phase) componen t and a quadrature-phase (Q-phase) component. The complex exponential sequence is generated, in one embodiment, by employing a SIN/COS look up table that is driven by a phase difference signal generated by the digital vector tracking phase-locke d loop. A residual direct current (dc) component in the I-phase component caused by th e pilot signal is removed, resulting in a baseband I/Q signal. A technical advantage of this carrier recovery invention is that the bandwidth of the phase-locked loop filter can be different for the acquisition mode and the tracking mode. This allows for optimal performance in both the acquisition and tracking modes of operation.