HDTV signal receiver with imaginary-sample-presence detector for QAM/VSB mode selection
First Claim
1. 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, comprising:
- a tuner for selecting said selected digital HDTV signal, irrespective of whether it is quadrature-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal, and converting it to a final intermediate-frequency (IF) signal;
an analog-to-digital converter for digitizing said final IF signal to generate a digitized final IF signal;
QAM synchrodyning circuitry for generating real and imaginary sample streams of interleaved QAM symbol code, by synchrodyning said digitized final IF signal to baseband providing it is a QAM signal and otherwise processing said digitized final IF signal as if it were a QAM signal to be synchrodyned to baseband;
VSB synchrodyning circuitry for generating real and imaginary sample streams of interleaved VSB symbol code, by synchrodyning said digitized final IF signal to baseband providing it is a VSB signal and otherwise processing said digitized final IF signal as if it were a VSB signal to be synchrodyned to baseband;
first squaring means for squaring each sample in said imaginary sample stream from said VSB synchrodyning circuitry to generate a corresponding sample of a first squared-sample signal;
a first digital lowpass filter, connected for supplying a first lowpass filter response to said first squared-sample signal;
a threshold detector responsive to said first lowpass filter response for generating a control signal, said control signal being in a first condition when said first lowpass filter response is not below a threshold value and being in a second condition when said first lowpass filter response is below said threshold value;
means responding to said control signal being in a first condition for automatically switching the radio receiver to operate in a QAM signal reception mode; and
means responding to said control signal being in a second condition for automatically switching the radio receiver to operate in a VSB signal reception mode.
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Accused Products
Abstract
A radio receiver for receiving a selected digital HDTV signal, irrespective of whether it is a complex-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal, using the same tuner. The final IF signal from the tuner is digitized for application to in-phase and quadrature QAM synchronous detectors and to in-phase and quadrature VSB synchronous detectors. The carrier frequencies of the QAM and VSB final IF signals are regulated to be submultiples of symbol frequency by applying automatic frequency and phase control signals developed in the digital circuitry to a local oscillator of the tuner. The mean average energy in the output samples of the quadrature VSB synchronous detector is sensed for automatically switching the radio receiver reception mode, for operation in a VSB HDTV signal reception mode when the mean average energy is below a threshold level, and for operation in a QAM signal reception mode when the mean average energy is not below the threshold level.
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Citations
32 Claims
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1. 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, comprising:
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a tuner for selecting said selected digital HDTV signal, irrespective of whether it is quadrature-amplitude-modulation (QAM) or a vestigial sideband (VSB) signal, and converting it to a final intermediate-frequency (IF) signal; an analog-to-digital converter for digitizing said final IF signal to generate a digitized final IF signal; QAM synchrodyning circuitry for generating real and imaginary sample streams of interleaved QAM symbol code, by synchrodyning said digitized final IF signal to baseband providing it is a QAM signal and otherwise processing said digitized final IF signal as if it were a QAM signal to be synchrodyned to baseband; VSB synchrodyning circuitry for generating real and imaginary sample streams of interleaved VSB symbol code, by synchrodyning said digitized final IF signal to baseband providing it is a VSB signal and otherwise processing said digitized final IF signal as if it were a VSB signal to be synchrodyned to baseband; first squaring means for squaring each sample in said imaginary sample stream from said VSB synchrodyning circuitry to generate a corresponding sample of a first squared-sample signal; a first digital lowpass filter, connected for supplying a first lowpass filter response to said first squared-sample signal; a threshold detector responsive to said first lowpass filter response for generating a control signal, said control signal being in a first condition when said first lowpass filter response is not below a threshold value and being in a second condition when said first lowpass filter response is below said threshold value; means responding to said control signal being in a first condition for automatically switching the radio receiver to operate in a QAM signal reception mode; and means responding to said control signal being in a second condition for automatically switching the radio receiver to operate in a VSB signal reception mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification