Digital quadrature radio receiver with two-step processing

Claim 2

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 f a ; analog-to digital converter means operating at a fixed sampling rate f s 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 f s /2, said first digital IF signal having a center frequency f d1 about equal to f s /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 f d2 within the frequency range from -f s /8 to +f s /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 f s /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.

Claim 3

A receiver for receiving stereo signals broadcast in the C-QUAM format comprising: tuner means for receiving said analog broadcast signal and generating an analog C-QUAM intermediate frequency (IF) signal having a frequency f a ; analog-to-digital converter means operating at a fixed sampling rate f s 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 f s /2, said first digital IF signal having a center frequency f d1 ; 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 -f s /8 to +f s /8 and having a center frequency f d2 , 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 f s /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.

Claim 4

A receiver for receiving stereo signals broadcast in the C-QUAM format comprising: tuner means for receiving said analog broadcast signal and generating an analog C-QUAM intermediate frequency (IF) signal having a frequency f a ; analog-to-digital converter means operating at a fixed sampling rate f s 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 f s /2, said first digital IF signal having a center frequency f d1 ; 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 -f s /8 to +f s /8 and having a center frequency f d2 , 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 f s /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.

Claim 5

The receiver of claim 2 wherein said concurrent means is comprised of a finite impulse response filter.

Claim 6

The receiver of claim 3 wherein said weights concurrently provide an anti-aliasing filter function.

Claim 7

The receiver of claim 2 wherein f d1 is about equal to f s /4 and f d2 is nearly equal to zero.

Claim 8

The receiver of claim 2 further comprising: matrix means coupled to said envelope detector and said conversion means for generating said stereo signals from said envelope signal and said QUAM signal.

Claim 9

The receiver of claim 6 further comprising digital-to-analog converter means coupled to said matrix means for generating analog stereo signals.

Claim 10

The receiver of claim 2 wherein said conversion means comprises: implicit calculating means coupled to said envelope detector and said synchronous detector for generating a correction signal using implicit feedback; and multiplier means coupled to said synchronous detector and said implicit calculating means for multiplying said synchronous-detector Q signal and said correction signal to generate a QUAM signal corresponding to the difference of said stereo signals.

Claim 11

The receiver of claim 2 wherein said conversion means comprises: comparing means coupled to said envelope detector and said synchronous detector for generating a correction signal based on the error between said envelope signal and said synchronous-detector I signal; multiplier means coupled to said synchronous detector and said comparing means for multiplying said synchronous-detector Q signal and said correction signal to generate a QUAM signal corresponding to the difference of said stereo signals.

Claim 12

The receiver of claim 2 wherein said conversion means comprises: divider means coupled to said synchronous detector for dividing said synchronous-detector Q signal by said synchronous-detector I signal to generate a divider signal; and multiplier means coupled to said divider means and said envelope detector for multiplying said divider signal and said envelope signal to generate a QUAM signal corresponding to the difference of said stereo signals.

Claim 13

The receiver of claim 2 further comprising stereo detect means coupled to said conversion means for detecting the presence of a stereo pilot signal in said QUAM signal.

Claim 14

The receiver of claim 11 further comprising blend control means coupled to said stereo detect means for selecting stereo or monophonic reception in accordance with the detection of said stereo pilot signal by said stereo detect means.

Claim 15

The receiver of claim 2 wherein said synchronous detector comprises: loop filter means coupled to said conversion means for filtering said QUAM signal; oscillator means coupled to said loop filter means for producing sine and cosine signals locked to the frequency and phase of said QUAM signal; and complex mixer means coupled to said oscillator means and said concurrent means for mixing said complex IF signal with said sine and cosine signals to produce said detected C-QUAM signal.

Claim 18

The method of claim 14 wherein f d1 is about equal to f s /4 and f d2 is about equal to zero.