Abstract: In an NTSC digital television receiver, the composite video signal is digitized with a sampling frequency of 32/13 times the color subcarrier frequency, f.sub.c. The chrominance signal component of this video signal is demodulated using a pair of finite impulse responsive filters having programmable weighting factors. The weighting factors are changed in a 32 step sequence as 32 consecutive chrominance samples are applied to the filters. The circuitry which generates the weighting factors is responsive to a phase alignment signal to determine when the 32 step sequence begins.

Abstract: A sampled data filter used in a television automatic ghost cancellation system employs a single chain of cascaded delay elements and a crossbar switch matrix to implement the several different delayed sequences of samples that are used by the system to cancel several ghost signals. The rows of switch elements in the crossbar switch matrix are coupled to the individual delay elements, and the columns of the matrix are coupled to sample scaling circuitry. The scaled samples are summed to develop a psuedo-ghost signal which is combined with the input signal to cancel the ghost signal components.

Abstract: A digital television receiver, having a line locked clock, includes a first digital phase locked loop which regenerates quadrature phase related subcarrier signals that are used to synchronously demodulate the chrominance signal components of composite video signals into color information signals. When nonstandard video signals (e.g., from a video tape recorder) are processed by the receiver, frequency instabilities in the line locked clock signal may cause the color information signals to be distorted. To compensate for this distortion, a second phase locked loop is synchronized to a reference signal generated by an analog oscillator. The analog reference signal is linearly added to baseband analog video signals provided by a tuner. The combined signals are digitized by an analog-to-digital converter and then filtered by parallel low-pass and band-pass filters to develop digital signals representing the video signals and the reference signal, respectively.

Abstract: A television deghosting system includes an IIR filter having programmable filter coefficients which processes the input signals to remove ghost signal components. The IIR filter may be reconfigured as an FIR filter, having its coefficient and delay values changed to operate as a matched correlation filter. In this mode the filter is used to correlate a training signal to determine the relative delays of ghost signals with respect to the direct signal. The training signal used is the sum of the squared differentials of the in-phase and quadrature-phase components of the video IF signal during an interval defined by the leading edge of the vertical sync pulse and the first equalization pulse.

Abstract: A digital television receiver includes a first phase locked loop which develops a sampling clock signal that is locked to the horizontal line synchronizing signals components of a composite video signal. A second digital phase locked loop is clocked by the sampling clock signal and develops a digital signal that is phase locked to the color burst signal. This signal is used as a regenerated color subcarrier signal to synchronously demodulate the chrominance components of the composite video signal into I and Q color difference signals. To compensate for frequency instabilities in the regenerated subcarrier signal caused by frequency instabilities in the line-locked clock signal, a third digital phase locked loop develops an oscillatory signal which is phase locked to a reference signal generated by a crystal controlled oscillator. Control signals from the third phase locked loop are applied to circuitry which develops control signal that is independent of the crystal frequency.

Abstract: A digital television receiver includes a first phase locked loop which develops a sampling clock signal that is locked to the horizontal line synchronizing signal components of a composite video signal. A second digital phase locked loop is clocked by the sampling clock signal and develops a digital signal that is phase locked to the color burst signal. This digital signal is used as a regenerated color subcarrier signal to synchronously demodulate the chrominance components of the composite video signals into I and Q color difference signals. To compensate for frequency instability in the regenerated subcarrier signal caused by frequency instabilities in the line-locked clock signal, a third digital phase locked loop develops an output signal which is phase locked to a reference signal generated by a crystal controlled oscillator.

Abstract: A television receiver which includes an automatic deghosting system synchronously demodulates IF television signals to generate baseband signals representing the in-phase and quadrature phase modulation components of the IF signals. A signal representing the phase difference between the carrier of the signal as broadcast and the carrier of the received signal, which may include ghosts, is generated from the in-phase and quadrature signals. This signal is applied to circuitry which develops signals proportional to the sine and cosine of the phase angle separating the broadcast carrier phase and the received carrier phase. The demodulated in-phase and quadrature phase baseband signals are multiplied by the sine and cosine signals in a complex multiplier to correct distortion resulting from the synchronous demodulation using the carrier of the received signal.

Abstract: A digital television signal deghosting system includes an IIR filter responsive to the in-phase and quadrature-phase components of modulated television signals for cancelling ghost signals irrespective of their phase. A double-conversion tuner develops modulated composite video signals having a 3f.sub.c carrier frequency. An analog-to-digital converter responsive to a two-phase 3f.sub.c clock signal develops digital samples which alternately represent the baseband in-phase and quadrature-phase components of the modulated video signals. These samples are separated to develop digital signals representing the in-phase and quadrature-phase components of the modulated television signals.

Abstract: An automatic deghosting system synchronously demodulates IF television signals to generate baseband composite video signals. A strong RF ghost signal having a carrier phase that differs from that of the desired signal may cause demodulation phase errors, causing quadrature distortion in the baseband video signals. The circuitry shown in this disclosure synchronously demodulates the quadrature component of the IF television signals and develops a signal proportional to the difference between the values of the baseband quadrature signal immediately before and immediately after the leading edge of the vertical sync pulse. This signal, which is proportional to the demodulation phase error, is used to control a phase locked loop that regenerates the in-phase and quadrature carrier signals used by the synchronous demodulators to substantially eliminate any demodulation phase error.

Abstract: A digital television receiver, having a line-locked clock, includes a partly digital, partly analog phase locked loop. This phase locked loop regenerates two quadrature phase related subcarrier signals that are used to synchronously demodulate the chrominance signal components of the composite video signals into two color informaiton signals. The phase locked loop includes an analog voltage controlled oscillator which generates a signal that is independent of any frequency instability in the line locked clock signal. An analog-to-digital converter digitizes this signal to provide one of the subcarrier signals. This subcarrier signal is applied to a read-only memory to generate the second subcarrier signal. The two color information signals are obtained by multiplying the chrominance signals by the first and second subcarrier signals.

Abstract: Apparatus and a method for controlling the field or frame store signal processing of standard and nonstandard video signals is disclosed. The apparatus includes a nonstandard signal detector which compares the received horizontal sync signals to a horizontal sync signal generated internally be counting down a clock signal having a frequency proportional to the color subcarrier frequency. The detector produces a control signal which is in one state when the horizontal sync signals are substantially in coincidence and in a second state otherwise. This control signal is applied to apparatus which switches from field or frame store signal processing apparatus to alternative signal processing apparatus, which does not include a field or frame memory, to minimize distortion of the image when nonstandard signals are processed.

Abstract: A pix-in-pix television display includes a memory for holding samples representing one field of the small picture. Samples which are to be written into the memory are developed in a buffer memory one line at a time over intervals corresponding to the three line periods of the signal which produces the small picture. A line of samples is written from the buffer memory into the field memory over three line periods of the small picture signal. The memory write operation is suspended when data is read from the field memory for display. The write operation resumes when a read operation is completed at the address and pixel value which were being written when the write operation was suspended.

Abstract: A pix-in-pix television display includes circuitry for reducing the amount of memory needed to hold one field of the reduced size image. In the display apparatus, digital samples representing the large and small picture signals are developed at substantially equal rates by separate circuitry. Subsampling circuitry stores one out of every five of the samples representing a horizontal line of the small picture. These samples are displayed, synchronous with the large picture at a rate three-fifths times the display rate of the large picture samples to produce an apparent size reduction of one-third in the horizontal direction.

Abstract: Arc-over in the cathode ray tube of a digital television receiver produces a large current pulse which, when it discharges via the chassis ground, disrupts the reference ground potentials of other circuitry coupled to the chassis ground. The affected circuitry includes digital data storage elements which may experience random state changes caused by the fluctuating ground potential. The CRT arc-over condition is detected by circuitry which applies a pulse to the reset terminal of the microprocessor, causing it to restore the potentially corrupted data in the data storage elements using preset data stored in a less volatile programmable read only memory.

Abstract: A pix-in-pix television display, with a digital memory for holding samples representing one field of the small picture, includes circuitry for converting eight-bit luminance samples into five-bit samples for efficient storage in the digital memory. A subtracter subtracts a predetermined block level bias value from each sample and an adder adds a two bit psuedo-random dither value to each sample. The six most significant bits of these samples are applied to a limiter which changes the samples having values greater than thirty-one to have values of thirty-one. The five-bit luminance samples are obtained by taking the five least significant bits of the samples provided by the limiter.

Abstract: A pix-in-pix display includes a filtering system for processing the video signals which produce the reduced-size image. The filtering system includes an anti-aliasing filter which reduces the amplitude of the components of the video signals which may cause aliasing distortion when the image is subsampled. However, the filter passes substantial amounts of these components. The filtered video signal is subsampled and applied to a peaking filter which amplifies the band of frequencies containing the aliasing components relative to lower frequency bands to improve the appearance of detailed portions of the reproduced image.

Abstract: A digital deghosting system uses the interval between the sixth pre-equalization pulse and the first serration as a training signal to determine the timing and amplitude of ghost signals relative to the desired signal. The system includes level shifting circuitry to change the amplitude of the video signals during the training interval. This amplitude shift ensures that all of the information concerning the ghost signals is within the dynamic range of the analog to digital converter.

Abstract: A digital television receiver, which uses a comb filter to separate the luminance and chrominance components of composite video signals, includes an adaptive band-pass filter for processing the comb filtered chrominance signals. Comb filtered chrominance signals may include luminance vertical detail information at the relatively high frequencies also occupied by chrominance information. The adaptive band-pass filter is controlled to have a narrow bandwidth when significant amounts of this relatively high frequency vertical detail information are present and to have a wide bandwidth otherwise. Consequently, the bandwidth of the chrominance signal provided by this filter is restricted only when it is necessary to prevent distortion, and vertical detail is added to the luminance signal only when it is not likely to be contaminated with chrominance information.

Abstract: A narrow bandwidth analog-to-digital conversion (ADC) system is described in the context of the color burst processing and burst phase detecting circuitry of a digital color television receiver. The ADC includes a dither generator which adds a dither signal to either the analog input signal or to the reference signal used by the ADC. This dither signal increases in magnitude by 1/16 of an LSB value at a rate one-quarter of the burst frequency and changes in sign at one-half of the burst frequency. This signal passes through a low-pass filter in the chrominance channel providing an increase in sample resolution by averaging the samples in a chroma band-pass filter and in the phase detecting circuitry.

Abstract: System performance of picture-in-picture video display systems is dependent on critical timing relationships between the incoming signals and the clock signals used to sample and display both the large picture and small picture signals. Video signals from various sources, e.g. VTR's, tend to have jittering time bases which may cause the small image to appear jagged or tilted. This distortion in the small image may be reduced by effecting adaptive signal delays in the small picture signal responsive to the relative phase of the system clock signal with respect to the horizontal synchronizing pulses of the large and/or small picture signal. One phase measure is used to control an interpolator which combines successive samples of the small picture signal in proportions to develop sample values corresponding to samples that would have occurred had the small picture signal been sampled by a clock properly aligned to the small picture horizontal synchronizing pulses.