US Patent 7421042 Carrier tracking loop lock detector

An ATSC (Advanced Television Systems Committee) VSB (Vestigial Sideband) receiver includes a carrier tracking loop (CTL) for processing a received ATSC VSB signal and a CTL lock detector. The CTL lock detector includes an averaging filter for averaging the down-converted received ATSC VSB signal to provide a DC offset, an estimator for providing an estimate of the DC offset, and a comparator for providing a lock signal as a function of a comparison between the estimate of the DC offset and the DC offset, wherein the lock signal is representative of either a locked condition or an unlocked condition of the CTL.