Digital quadrature radio receiver with two-step processing
First Claim
Patent Images
1. A receiver for digitally processing an analog radio-frequency (RF) broadcast signal comprising:
- tuner means for receiving said analog RF broadcast signal and generating an analog intermediate frequency (IF) signal having a frequency fa ;
analog-to digital converter means operating at a fixed sampling rate fs and coupled to said tuner means for converting said analog IF signal to a first digital IF signal comprised of a plurality of samples, said first digital IF signal being contained in the frequency range between zero and fs /2, said first digital IF signal having a center frequency fd1 about equal to fs /4;
concurrent complex mixing, filtering, and sample-rate reducing means coupled to said analog-to-digital converter means for generating a complex IF signal having a near-zero center frequency fd2 within the frequency range from -fs /8 to +fs /8, said complex IF signal having an in-phase component I and a quadrature-phase component Q each being formed from weighted alternate samples of said first digital IF signal according to a set of predetermined weights, said weights corresponding to a complex nonsynchronous mixing signal having a frequency equal to fs /4 and corresponding to a reduction in sampling rate by a whole multiple of 4; and
second complex mixing means coupled to said concurrent means for synchronously detecting said complex IF signal, said second complex mixing means including a variable oscillator producing sine and cosine signals locked to the frequency and phase of said complex IF signal.
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Abstract
A digital signal processing (DSP) radio receiver employs a conventional analog RF tuner to produce an analog intermediate frequency. The receiver performs DSP functions of digitally sampling the analog intermediate frequency at a sampling rate fs, concurrently mixing, filtering, and sample-rate reducing the sampled intermediate frequency using a digital filter for inherently generating a near-zero complex intermediate frequency signal, and synchronously detecting the complex IF signal. In a preferred embodiment, the invention is employed to reproduce AM stereo signals.
197 Citations
15 Claims
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1. A receiver for digitally processing an analog radio-frequency (RF) broadcast signal comprising:
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tuner means for receiving said analog RF broadcast signal and generating an analog intermediate frequency (IF) signal having a frequency fa ; analog-to digital converter means operating at a fixed sampling rate fs and coupled to said tuner means for converting said analog IF signal to a first digital IF signal comprised of a plurality of samples, said first digital IF signal being contained in the frequency range between zero and fs /2, said first digital IF signal having a center frequency fd1 about equal to fs /4; concurrent complex mixing, filtering, and sample-rate reducing means coupled to said analog-to-digital converter means for generating a complex IF signal having a near-zero center frequency fd2 within the frequency range from -fs /8 to +fs /8, said complex IF signal having an in-phase component I and a quadrature-phase component Q each being formed from weighted alternate samples of said first digital IF signal according to a set of predetermined weights, said weights corresponding to a complex nonsynchronous mixing signal having a frequency equal to fs /4 and corresponding to a reduction in sampling rate by a whole multiple of 4; and second complex mixing means coupled to said concurrent means for synchronously detecting said complex IF signal, said second complex mixing means including a variable oscillator producing sine and cosine signals locked to the frequency and phase of said complex IF signal.
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2. A receiver for receiving stereo signals broadcast in the C-QUAM format comprising:
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tuner means for receiving said analog broadcast signal and generating an analog C-QUAM intermediate frequency (IF) signal having a frequency fa ; analog-to-digital converter means operating at a fixed sampling rate fs and coupled to said tuner means for converting said analog IF signal to a first digital IF signal comprised of a plurality of samples, said first digital IF signal being contained in the frequency range between zero and fs /2, said first digital IF signal having a center frequency fd1 ; concurrent complex mixing, filtering, and sample-rate reducing means coupled to said analog-to-digital converter means for generating a complex IF signal within the frequency range from -fs /8 to +fs /8 and having a center frequency fd2, said complex IF signal having an in-phase component I and a quadrature-phase component Q each being formed from weighted alternate samples of said first digital IF signal according to a set of predetermined weights, said weights corresponding to a complex nonsynchronous mixing signal having a frequency equal to fs /4 and corresponding to a reduction in sampling rate by a whole multiple of 4; a synchronous detector demodulating said complex IF signal to produce a detected C-QUAM signal including a synchronous-detector I signal and a synchronous-detector Q signal, said detected C-QUAM signal having a phase-locked center frequency at substantially zero; an envelope detector generating an envelope signal corresponding to the envelope of said broadcast signal; and conversion means coupled to said synchronous detector and said envelope detector for converting said detected C-QUAM signal to a QUAM signal. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for digitally processing an AM stereo signal received as an analog broadcast signal using quadrature encoding of stereo information, said method comprising the steps of:
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receiving said analog broadcast signal; generating an analog intermediate frequency (IF) signal having a center frequency fa ; converting said analog IF signal to a first digital IF signal at a fixed sampling rate fs, said first digital IF signal being contained in the frequency range between zero and fs /2, said first digital IF signal having a center frequency fd1 ; filtering said first digital IF signal in a digital filter to obtain a complex IF signal within the frequency range from -fs /8 to +fs /8 and having a center frequency fd2, said complex IF signal having an in-phase component I and a quadrature-phase component Q each being formed from weighted alternate samples of said first digital IF signal according to a set of predetermined weights, said weights corresponding to a complex nonsynchronous mixing signal having a frequency equal to fs /4 and concurrently corresponding to a reduction in sampling rate by a whole multiple of 4; synchronously demodulating said complex IF signal to obtain a demodulated baseband signal; detecting an envelope of-said broadcast signal to generate an envelope signal; modifying said demodulated baseband signal in accordance with said envelope signal; and recovering said stereo information from said modified demodulated baseband signal. - View Dependent Claims (15)
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Specification