Abstract: A phase detector that uses symbol sign information to aid the phase error detection process to determine a phase error of a complex signal such as a vestigial side band (VSB) signal. The phase detector comprises a subtractor having one input coupled to the I signal (i.e., an unquantized digital value that is sometimes referred to as a quasi-analog signal) and a second input coupled to the data output of a slicer (quantizer) representing the magnitude of a sample point within a symbol (i.e., a digital value representing one of M levels of the VSB signal). The unquantized signal is subtracted from the quantized I signal to produce a &Dgr;I signal. The I signal is also processed to determine the sign of the present symbol. A before-after symbol processor determines the sign values of a previous (before) symbol and a later (after) symbol and compares those signs to the sign of the present symbol.

Abstract: An NTSC bandwidth-compatible HDTV system employs multiple quadrature amplitude modulation (QAM). A first suppressed QAM carrier is modulated with high priority information including predominantly low frequency information. A second suppressed QAM carrier is modulated with low priority information including predominantly high frequency information. The high priority QAM signal exhibits a larger amplitude and narrower bandwidth than the low priority QAM signal, and is disposed in the lower portion of the multiple QAM frequency spectrum normally occupied by the vestigial sideband of a standard NTSC television signal. The frequency spectrum of the multiple QAM signal exhibits signal attenuation at frequencies associated with high energy information in a standard NTSC signal, e.g., frequencies around the NTSC picture and sound carriers.

Abstract: A high definition television receiver including analog and digital signal processing circuits receives an analog high definition television signal representative of digital television information. The received signal contains narrowband high priority information and wideband low priority information. An automatic gain control (AGC) signal is developed from the narrowband information as a function of the values of coefficients of an associated adaptive equalizer, and as a function of the number of saturated samples processed by associated input analog-to-digital converters.

Abstract: A high definition television receiver including digital signal processing circuits receives a high definition television signal containing narrowband high priority information from which a system clock is derived, and low priority wideband information. After a channel change, a clock signal developed from narrowband information associated with the previously tuned channel is used as the receiver clock until a clock signal with a desired phase characteristic is developed from the narrowband information of the newly tuned channel.

Abstract: A system for synchronizing first and second video signals which are to be combined is disclosed. The second signal is data compressed digital signal containing macro blocks of composite data preceded by a field sync flag synchronized with the field rate of the first signal. Each macro block contains a video block including a plurality of image line blocks. Each line block contains multiplexed video data such as luminance and chrominance information preceded by a marker flag. The flag preceding the first line block in a video block is a field flag which identifies the beginning of a scanning field associated with that video block. The flags preceding other line blocks in that video block identify the other line blocks respectively. Each flag contains a unique data preamble which identifies the associated line block. Illustratively, field flag data includes unique header, field number, and "performance index" data for controlling data quantization.

Abstract: A digital phase synchronization system in which a received pulse wave is compared in a phase detector with a local pulse wave obtained by frequency dividing the output of a local oscillator. One output of the phase detector is used to control the subtraction or addition of pulses from the local oscillator until phase synchronization is achieved. Another output of the phase detector is used to control the number of pulses which are subtracted or added. The number of pulses subtracted or added is proportional to the phase difference when the phase difference is greater than a predetermined value, and is limited to one or a few pulses when the phase difference is below the predetermined value.