Digital IF demodulator
View Patent ↗A digital IF demodulator includes an analog-to-digital (A/D) converter that receives an analog IF signal and converts it to a digital IF signal. A parallel multiplier then down-converts the digital IF signal to a baseband signal having a video component and an audio component. The frequency down-conversion uses a parallel multiplier driven by an outer feedback loop that corrects gross frequency errors in said digital IF signal. The digital IF demodulator also includes a video recovery circuit that selects the video component from the baseband signal and further down-converts the baseband signal to a video baseband using a video complex mixer driven by an inner feedback loop that corrects fast phase perturbations in the video recovery circuit. Finally, the digital IF demodulator includes an audio recovery circuit that (i) receives said baseband signal from the parallel multiplier, and (ii) down-converts the audio component to an audio baseband signal using an audio complex mixer.
1. A digital IF demodulator, including:
means for converting an analog IF signal to a digital IF signal;
means for down-converting said digital IF signal to a baseband signal having a video component and an audio component, said means for down-converting including means for correcting gross frequency errors in said digital IF signal;
means for selecting said video component from said baseband signal; and
means for down-converting said video component to a video baseband signal, including a means for correcting fast phase perturbations in said digital IF signal.
2. The digital IF demodulator of claim 1 , further comprising:
means for down-converting said audio component to an audio baseband signal.
3. The digital IF demodulator of claim 1 , wherein said means for correcting a gross frequency error, includes:
means for generating an outer loop oscillator signal based on feedback from said video baseband signal, so as to center a down-converted digital IF signal in a video filter of said means for selecting said video component.
4. The digital IF demodulator of claim 1 , wherein said means for correcting fast phase perturbations in said digital IF signal, includes:
means for generating an inner loop oscillator signal based on feedback from said video baseband signal, so as to center said video baseband signal in the passband of a corresponding output filter.
5. The digital IF demodulator of claim 4 , wherein said means for generating said outer loop oscillator signal is based on said inner loop oscillator signal.
6. The digital IF demodulator of claim 4 , wherein said means for generating an inner loop oscillator signal is more responsive to changes in said video baseband signal than said means for generating said outer loop oscillator signal.
7. The digital IF demodulator of claim 4 , wherein said means for generating an inner loop oscillator signal has a defective filter pole so that accumulated gross frequency offsets leak to said means for generating an outer loop oscillator.
8. The digital IF demodulator of claim 4 , wherein at least one of said means for generating an outer loop oscillator signal and said means for generating an inner loop oscillator signal include a sine/cosine look-up table coupled to an output of a numerically controlled oscillator.
9. The digital IF demodulator of claim 1 , further comprising:
means for variably amplifying said analog IF signal, responsive to an amplitude of said video baseband signal.
10. The digital IF demodulator of claim 9 , wherein a gain of said means for amplifying is determined to use a full dynamic range of said means for converting.
11. The digital IF demodulator of claim 1 , wherein said digital IF demodulator is at least partially disposed on a silicon substrate, according to a Complementary Metal Oxide Semiconductor (CMOS) process.
12. The digital IF demodulator of claim 1 , wherein said audio component of said digital IF signal includes an audio carrier that is offset in frequency from a picture carrier in said video component of said digital IF signal.
13. The digital IF demodulator of claim 12 , wherein said audio carrier is offset from said picture carrier by approximately 4.5 MHz.
14. The digital IF demodulator of claim 12 , wherein said audio carrier is offset from said picture carrier by approximately 5.5 MHz.
15. The digital IF demodulator of claim 12 , wherein said audio carrier is offset from said picture carrier by approximately 6.0 MHz.
16. The digital IF demodulator of claim 12 , wherein said audio carrier is offset from said picture carrier by approximately 5.0 MHz.
17. The digital IF demodulator of claim 1 , wherein said means for correcting gross frequency errors includes a first feedback loop for correcting gross frequency errors in said digital IF signal.
18. The digital IF demodulator of claim 17 , wherein said means for correcting fast phase perturbations includes a second feedback loop for correcting fast phase perturbations in said digital IF signal, wherein said second feedback loop is different from said first feedback loop.