Abstract: A radio receiver uses the same tuner for receiving a selected digital television (DTV) signal, irrespective of whether it is a quadrature-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal. The tuner supplies a final IF signal in a 6-MHz-wide frequency band, the lowest frequency of which is not appreciably more than 2.69 MHz. The final IF signal is digitized at a rate that is a multiple of both the symbol frequencies of the QAM and VSB signals, for synchrodyning to baseband, with the 2.69 MHz difference between the carrier frequencies of QAM and VSB signals being taken into account in the digital synchrodyning circuitry. The carrier frequencies of the QAM and VSB final IF signals are regulated to be submultiples of the multiple of both the symbol frequencies of the QAM and VSB signals by applying automatic frequency and phase control signals developed in the digital circuitry to a local oscillator of the tuner.

Abstract: During a period of transition from broadcasting analog TV signals to broadcasting digital TV signals, digital TV reception is susceptible to disruption owing to co-channel interference by analog TV signals. During this same transition period usually a digital TV receiver will incorporate an auxiliary analog TV receiver. This auxiliary analog TV receiver is advantageously used during digital TV signal reception for determining the amount of co-channel interference by analog TV signals, so that comb filtering can be selectively applied to symbol coding recovered from the digital TV signal, for suppressing artifacts of co-channel interfering analog TV signal when they are large enough to have substantial adverse on symbol decoding. The amount of NTSC co-channel interference is estimated by detecting the level of intercarrier generated by mixing the audio and video signals of the analog TV signal.

Abstract: An adaptive filter or equalizer for digital data communication includes, a first cascade circuit connected to operate as a digital finite-impulse-response (FIR) filter, the first cascade circuit having a respective first single input for receiving samples of complex input data, a respective second input composed of a first plurality of input taps for receiving filter weighting signals, and a respective output for producing samples of filtered data. An error signal generator responds to samples supplied from the output of first cascade circuit to generate samples of an error signal.

Abstract: A method for detecting when a digital television signal is accompanied by co-channel interfering NTSC signal of substantial amplitude is described for use in a digital television receiver. The video portion of any co-channel interfering NTSC signal is synchrodyned to baseband, for generating an in-phase demodulation result including first artifacts of the digital television signal, and for generating a quadrature-phase demodulation result including second artifacts of the digital television signal. The quadrature-phase demodulation results are phase shifted by 90.degree. at frequencies in a prescribed frequency range before being linearly combined with the in-phase quadrature-phase demodulation results, to generate a linear combining result substantially free of the first and second artifacts of the digital television signal in the prescribed frequency range.

Abstract: Automatic gain control (AGC) for a quadrature-amplitude-modulation (QAM) digital radio receiver, such as used for receiving digital high-definition television transmissions, is provided immunity to the effects of the ringing of intermediate-frequency (IF) amplifiers at carrier frequency in response to impulse noise. The energy associated with the ringing of the IF amplifiers is at frequencies relatively close to the carrier of the IF signal as compared to data modulation. Filtering that suppresses the energy associated with the ringing of the IF amplifiers is used to recover information concerning the envelope variations of the QAM signal free from accompanying ringing energy, which envelope variations are then peak detected to develop AGC signals for the QAM digital radio receiver.

Abstract: During a period of transition from broadcasting analog TV signals to broadcasting digital TV signals, digital TV reception is susceptible to disruption owing to co-channel interference by analog TV signals. During this same transition period usually a digital TV receiver will incorporate an auxiliary analog TV receiver. This auxiliary analog TV receiver is advantageously used during digital TV signal reception for determining the amount of co-channel interference by analog TV signals, so that comb filtering can be selectively applied to symbol coding recovered from the digital TV signal, for suppressing artifacts of co-channel interfering analog TV signal when they are large enough to have substantial adverse on symbol decoding. The amount of co-channel interference is estimated from synchronously detected analog TV signal.

Abstract: Post-coder selection circuitry uses an NTSC interference detector for controlling the selection of whether post-coding is to precede trellis decoding in an HDTV receiver. The NTSC interference detector includes an NTSC extracting filter for supplying an NTSC extracting filter response that separates accompanying co-channel interfering NTSC signal component from the received I-channel baseband signal including its direct bias component. The NTSC interference detector includes a comparing portion for periodically integrating the NTSC extracting filter response and deciding whether the co-channel interfering NTSC signal component from the I-channel baseband signal is above a first reference value or not.

Abstract: A video signal receiver with reduced sensitivity to interference from co-channel digital TV signals includes circuitry for selecting a vestigial sideband amplitude-modulation signal descriptive of a video signal, converting the selected VSB AM signal to an intermediate frequency signal, and amplifying the IF signal to provide an amplified IF signal. The VSB AM signal is selected from any single one of a plurality of channels which can contain co-channel interference from a digital television signal. The amplified IF signal is synchronously detected with respect to video carrier frequency for generating an in-phase synchronous detection response and for generating a quadrature-phase synchronous detection response. All frequency components of the quadrature-phase synchronous detection response above a prescribed frequency are phase shifted substantially 90.degree.

Abstract: Co-channel interference accompanying multiple-level symbols in a digital receiver, such as a digital television receiver, is suppressed by using a first comb filter to reduce the energy of the co-channel interference before data slicing. The first comb filter incidentally carries out a symbol re-coding procedure of first type that introduces error into the symbol decoding results generated by the data slicing. A second comb filter carries out a symbol re-coding procedure of second type after the data slicing to compensate for the symbol re-coding procedure of first type and generate corrected symbol decoding results. The symbol re-coding procedure of first type re-codes an input symbol stream through differential delay and first linear combination of the differentially delayed terms.

Abstract: In a radio receiver for receiving vestigial sideband (VSB) signals including symbol codes descriptive of digital signals, HDTV signals being exemplary of such VSB signals, a tuner provides for selecting one of channels at different locations in a frequency band used for transmitting such VSB signals. The tuner also includes mixers for performing plural conversion of the selected channel to a final intermediate-frequency signal, which is digitized by an analog-to-digital converter. A phase tracker, operative on narrow-bandpass filtered portions of the digitized final intermediate-frequency signal centering on its carrier frequency, suppresses an imaginary portion of the final intermediate-frequency signal, arising from multipath distortion or from phase incoherency in local oscillations used during frequency conversion.

Abstract: A radio receiver for receiving a selected digital HDTV signal, irrespective of whether it is a quadrature-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal, using the same tuner. The tuner supplies a final IF signal in a 6 MHz frequency band, the lowest frequency of which is not appreciably more than 2.27 MHz. The final IF signal is digitized at a rate that is a multiple of both the symbol frequencies of the QAM and VSB signals, for synchrodyning to baseband, with the 2.375 MHz difference between the carrier frequencies of QAM and VSB signals being taken into account in the digital synchrodyning circuitry. The carrier frequencies of the QAM and VSB final IF signals are regulated to be submultiples of the multiple of both the symbol frequencies of the QAM and VSB signals by applying automatic frequency and phase control signals developed in the digital circuitry to a local oscillator of the tuner.

Abstract: All except possibly the shortest code words in variable-length coding of Huffman type supplied in a codestream having data segments in which each successive code word comprises a pointer code segment followed by a target code segment are decoded in a plurality of successive steps, a plural-bit chunk each step.. Selection circuitry successively selects chunks of the pointer code segment and the target code segment of each codeword, determining the beginning of the pointer code segment of a first of the codewords responsive to a start of data segment command. The beginning of the pointer code segment of each further codeword is determined responsive to the accumulated bit-lengths of the complete codewords processed by the decoder since the start of data segment command, and the beginning of the target code segment of each codeword is determined with respect to the beginning of the pointer code segment of that same codeword by an indication of the bit-length of the pointer code segment of that same codeword.

Abstract: A light-in-weight portable television receiver or computer monitor has doors that close over its display screen, to facilitate it being transported by a child of nine or ten years age. The display screen is sustantially vertical during normal viewing. These doors have loudspeakers on their interior surfaces, which doors open out from the sides of the cabinet to space the loudspeakers further apart for better stereophonic sound reproduction.

Abstract: A system for reproducing a luminance signal from a medium containing a previously recorded luminance signal with a high-frequency portion thereof compressed in dynamic range includes a circuit for recovering that luminance signal from the medium. Filtering is done to separate the low-frequency and compressed-in-dynamic-range high-frequency portions of the recovered luminance signal from each other. A corer responds to the separated compressed-in-dynamic-range high-frequency portion of the recovered luminance signal to provide a cored high-frequency portion with expanded dynamic range and reduced noise.

Abstract: A tuner selects one of channels at different locations in a frequency band used for transmitting VSB HDTV signals including symbol codes descriptive of digital signals. The tuner also includes mixers for performing plural conversion of the selected channel to a final intermediate-frequency signal, which is digitized by an analog-to-digital converter. A phase tracker, operative on narrow-bandpass filtered portions of the digitized final intermediate-frequency signal centering on its carrier frequency, suppresses an imaginary portion of the final intermediate-frequency signal, arising from multipath distortion or from phase incoherence in local oscillations used during frequency conversion(s).

Abstract: BPSK modulation of suppressed carrier in quadrature with a video carrier amplitude-modulated by composite video signal is used for transmitting a serial-bit digital signal, which is subjected both to "pre-line-comb" and "pre-frame-comb" partial-response filtering prior to conversion to BPSK modulating signal. The "pre-frame-comb" partial-response filtering of the serial-bit data is done on a continuous basis, rather than transmitting frames of the BPSK twice, once in positive logic and once in negative logic, during successive pairs of consecutive frames of the NTSC television signal. This results in the full luminance bandwidth below chroma frequencies being available on average for the transmission of BPSK, rather than half that bandwidth.

Abstract: A switchable current amplifier comprising first and second transistors of complementary conductivity type, an input terminal connected to the emitter electrode of the first transistor, an output terminal to which the collector electrode of the second transistor connects, an inverting current amplifier having an input connection to which the emitter electrode of the second transistor connects and having an output connection to the base electrode of the first transistor. A control circuit is connected to an interconnection between the collector electrode of the first transistor and the base electrode of the second transistor for selectively diverting --in response to a control signal--collector current flow from said first transistor away from flowing as base current to the second transistor, thereby selectively disabling current amplification between the input and output terminals.

Abstract: A current mirror amplifier (CMA) and another current amplifier are connected in a degenerative current feedback loop with a point therein which point exhibits a low a-c impedance with respect to a-c ground and provides for sensing signal current applied thereto from an impedance element. The CMA has an input terminal connected to this sensing point, a common terminal connected to a-c ground and an output terminal connected to a constant current source load. The other current amplifier has input and common terminals connected to the CMA output terminal and to the sensing point, respectively, and has an output terminal from which sensed signal current is available.

Abstract: A three-terminal current amplifier with current-mode feedback to stabilize its current gain to be substantially independent of the common-emitter forward current gains of its component transistors. The feedback connection is made by means of a current splitter which includes a pair of emitter-connected transistors operated at substantially the same absolute temperature, T. These transistors have a potential substantially linearly proportional to T applied between their base electrodes. The current-amplifier output terminal is coupled to the interconnected emitter electrodes of the transistors and the collector electrode of the first transistor is coupled to the current-amplifier input terminal.

Abstract: A low output impedance precision dynamic voltage divider network having low power dissipation and particularly suited for fabrication on a monolithic integrated circuit chip.