METHOD AND APPARATUS FOR PROCESSING A TELEVISION SIGNAL WITH A COARSELY POSITIONED IF FREQUENCY

• US 20080225168A1
• Filed: 03/04/2008
• Published: 09/18/2008
• Est. Priority Date: 03/14/2007
• Status: Active Grant

• Current Assignee: Fresco Microchip, Inc. (Spectra7 Microsystems Inc.)
• Original Assignee: Fresco Microchip, Inc. (Spectra7 Microsystems Inc.)
• Inventors: Greggain, Lance, Selby, Steve, Ouslis, Chris, Shyshkin, Vyacheslav, Silver, Larry
• Granted Patent: US 8,570,446 B2
• Time in Patent Office: Days
• US Class Current: 348/554
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/42638 involving a hybrid front-end, e.g. analog and digital tuners
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 3/27 Circuits special to multi-standard receivers
• CPC Class Codes: H04N 5/211 Ghost signal cancellation H04N23/81 takes precedence
• CPC Class Codes: H04N 5/4446 IF amplifier circuits specially adapted for B&W TV RF amplifiers in general H03F3/189
• CPC Class Codes: H04N 5/46 for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27
• CPC Class Codes: H04N 5/91 Television signal processing therefor
• CPC Class Codes: H04N 9/642 Multi-standard receivers

Abstract

Various embodiments are described herein for a universal television receiver that is capable of processing television channel signals broadcast according to a variety of analog and digital broadcast standards. Analog processing includes using coarse filtering with pass bands that are wide enough to accommodate frequency shifts in a desired television channel signal and analog circuitry variability and digital processing includes tracking a carrier frequency of the desired television channel signal to generate and apply a frequency shift feedback signal to compensate for frequency shifts in the carrier frequency.

Claims

1. A television receiver for processing received television signals to provide video and audio information for a desired television channel signal, wherein the television receiver comprises:

an analog processing block for providing coarse filtering and amplification to a multi-channel television signal to produce a first signal, the coarse filtering being configured to use pass bands that are wide enough to accommodate frequency shifts in the desired television channel signal and analog circuitry variability;

an analog to digital converter coupled to the analog processing stage for digitizing the first signal to produce a second signal; and

a digital processing block coupled to the analog to digital converter for processing the second signal to obtain the video and audio information for the desired television channel signal,

wherein the receiver is configured to track a carrier frequency of the desired television channel signal and generate and apply a frequency shift feedback signal to compensate for frequency shifts in the carrier frequency.

2. The television receiver of claim 1, wherein the digital processing block is configured to additionally apply a known frequency shift for known frequency offset errors in the carrier frequency.

3. The receiver of claim 2, wherein the receiver further comprises an RF processing block coupled to the analog processing block for receiving broadcast television signals and providing amplification, filtering and mixing to generate the multi-channel television signal, wherein the RF processing block comprises a mixing stage having an oscillator with a coarse step size or a fine step size, and the digital processing block is further configured to compensate for the step size of the oscillator when generating the known frequency shift.

4. The television receiver of claim 1, wherein the analog processing block comprises at least one coarse bandpass filter or at least one coarse low pass filter for providing analog filtering.

5. The television receiver of claim 4, wherein the mixing stage comprises elements for providing an additional level of analog filtering.

6. The television receiver of claim 3, wherein the digital processing block is further configured to provide equalization for compensating for non-ideal analog filtering in at least one of the analog and RF processing blocks.

7. The television receiver of claim 2, wherein the first signal is a coarse channel signal, the second signal is a digitized coarse channel signal, and the digital processing block is further configured to process the digitized coarse channel signal to provide a processed digitized coarse channel signal, and the digital processing block comprises a video processing block having a frequency tracking loop for tracking the carrier frequency of the desired television channel signal, wherein the frequency tracking loop comprises:

a first frequency rotator for shifting the frequency content of the processed digitized coarse channel signal to the baseband based on the known frequency shift and additionally the frequency shift feedback signal for analog broadcast transmission standards;

a video filter stage for filtering the output of the first frequency rotator; and

a digital variable gain amplifier for amplifying the output of the video filter stage.

8. The receiver of claim 7, wherein the receiver further comprises a digital demodulator coupled to the digital processing block for processing the output of the digital variable gain amplifier and tracking the carrier frequency of the desired television channel signal to provide a digital transport stream in accordance with a digital television broadcast standard.

9. The receiver of claim 8, wherein the digital demodulator is further configured to generate and provide the frequency shift feedback signal to the first frequency rotator when the desired television channel signal is broadcast according to a digital television broadcast standard.

10. The receiver of claim 7, wherein the frequency tracking loop further comprises:

a second frequency rotator coupled to the digital variable gain amplifier for frequency shifting the output of the digital variable gain amplifier; and

a picture carrier recovery block coupled to the first and second frequency rotators, the picture carrier recovery block being configured to receive the output of the second frequency rotator, generate and provide the frequency shift feedback signal to the first frequency rotator and provide the video information of the desired television channel signal for analog broadcast transmission standards.

11. The receiver of claim 10, wherein the picture carrier recovery block comprises:

a carrier recovery filter configured to filter the output of the second frequency rotator to produce a filtered picture carrier signal;

a first phase rotator configured to apply phase adjustment to the filtered picture carrier signal to produce a phase-adjusted filtered picture carrier signal; and

a carrier recovery block coupled to the first phase rotator and the first frequency rotator, the carrier recovery block being configured to process the phase-adjusted filtered picture carrier signal to compensate for phase noise and produce a phase control signal that is provided to the first phase rotator to control the amount of the phase adjustment, the carrier recovery block further being configured to generate the frequency shift feedback signal.

12. The receiver of claim 10, wherein the picture carrier recovery-block comprises a carrier recovery block including:

a phase-frequency detector configured to receive an input phase signal based on the output of the second frequency rotator, generate a phase error signal by comparing the input phase signal with a reference phase signal, and generate a frequency error signal based on the phase error signal;

a summer configured to sum the frequency error signal and a version of the phase error signal to produce an adjusted frequency error signal;

a frequency loop amplifier configured to provide an amplified frequency error signal based on the adjusted frequency error signal; and

a frequency oscillator block configured to generate the frequency shift feedback signal based on the amplified frequency error signal.

13. The receiver of claim 12, wherein the frequency oscillator block comprises:

a frequency accumulator configured to update a current frequency based on the amplified frequency error signal to produce a frequency adjusted signal; and

a frequency clipping block configured to specify upper and lower limits for the frequency adjusted signal, and when the frequency adjusted signal exceeds one of the limits, the frequency clipping block is configured to limit the frequency adjusted signal to that limit,

wherein, the frequency shift feedback signal is generated based on the output of the frequency clipping block.

14. The receiver of claim 11, wherein the carrier recovery block further comprises:

a low pass filter configured to filter the phase error signal to produce a filtered phase error signal; and

a phase loop amplifier configured to amplify the filtered phase error signal to produce the version of the phase error signal.

15. The receiver of claim 7, wherein the digital processing block further comprises an audio filtering block having a second frequency tracking loop configured to extract an audio carrier frequency of the desired television channel signal for analog television broadcast standards and the audio filtering block is configured to apply a second known frequency shift to compensate for a known frequency offset in the audio carrier frequency.

16. The receiver of claim 15, wherein the second frequency tracking loop comprises:

a third frequency rotator for shifting the frequency content of the processed digitized coarse channel signal to the baseband;

an audio filter stage for filtering the output of the third frequency rotator;

a frequency demodulator coupled to the audio filter stage for demodulating the output of the audio filter stage and producing a first intermediate audio signal; and

an audio IF carrier recovery block that is configured to track the audio carrier signal that corresponds to the desired television channel signal based on one of the first intermediate audio signal and a sound IF carrier recovery signal, and to produce an audio frequency shift feedback signal which is provided to the third frequency rotator.

17. The receiver of claim 11, wherein the digital processing block further comprises an audio filtering block that is configured to process the output of the first frequency rotator to extract an audio carrier frequency of the desired television channel signal for analog television broadcast standards, wherein the processing is based on the phase control signal.

18. The receiver of claim 11, wherein the digital processing block further comprises an audio filtering block that is configured to process the output of the first frequency rotator to extract an audio carrier frequency of the desired television channel signal for analog television broadcast standards, wherein the audio filtering block comprises:

a third frequency rotator for shifting the frequency content of the frequency shift feedback signal to the baseband;

an audio filter stage for filtering the output of the third frequency rotator;

a frequency demodulator for demodulating the output of the audio filter stage and producing a first intermediate audio signal; and

an audio IF carrier recovery block that is configured to track the audio carrier signal that corresponds to the desired television channel signal.

19. A method of processing received television signals in a television receiver to provide video and audio information for a desired television channel signal, wherein the method comprises:

providing coarse filtering and amplification to a multi-channel television signal to produce a first signal, the coarse filtering being configured to use pass bands that are wide enough to accommodate frequency shifts in the desired television channel signal and analog circuitry variability in the television receiver;

digitizing the first signal to produce a second signal; and

processing the second signal to obtain the video and audio information for the desired television channel signal by tracking a carrier frequency of the desired television channel signal and generating and applying a frequency shift feedback signal to compensate for frequency shifts in the carrier frequency.

20. The method of claim 19, wherein the method further comprises additionally applying a known frequency shift for known frequency offset errors in the carrier frequency.

21. The method of claim 20, wherein the method comprises utilizing an RF processing block for receiving broadcast television signals and providing amplification, filtering and mixing to generate the multi-channel television signal, the RF processing block comprising a mixing stage having an oscillator with a coarse step size or a fine step size, and the method further comprises compensating for the step size of the oscillator when generating the known frequency shift.

22. The method of claim 19, wherein the step of providing coarse filtering and amplification comprises utilizing at least one coarse bandpass filter or at least one coarse low pass filter for providing analog filtering.

23. The method of claim 22, wherein the method further comprises providing the mixing stage with elements for providing an additional level of analog filtering.

24. The method of claim 19, wherein the processing step comprises providing equalization for compensating for non-ideal analog filtering.

25. The method of claim 20, wherein the first signal is a coarse channel signal, the second signal is a digitized coarse channel signal, and the method further comprises:

processing the digitized coarse channel signal to provide a processed digitized coarse channel signal;

shifting the frequency content of the processed digitized coarse channel signal to the baseband based on the known frequency shift and additionally the frequency shift feedback signal for analog broadcast transmission standards;

filtering the shifted frequency content of the processed digitized coarse channel signal with a video filter stage to produce a filtered signal; and

amplifying the filtered signal to produce an amplified signal.

26. The method of claim 25, wherein the method further comprises using a digital demodulator to process the amplified signal and track the carrier frequency of the desired television channel signal to provide a digital transport stream in accordance with a digital television broadcast standard.

27. The method of claim 26, wherein the method further comprises using the digital demodulator to generate and provide the frequency shift feedback signal when the desired television channel signal is broadcast according to a digital television broadcast standard.

28. The method of claim 25, wherein for analog broadcast transmission standards, the method further comprises:

frequency shifting the amplified signal to produce a frequency shifted amplified signal;

generating the frequency shift feedback signal based on the frequency shifted amplified signal and providing the frequency shift feedback signal to the first frequency rotator; and

filtering the frequency shifted amplified signal to provide the video information of the desired television channel signal.

29. The method of claim 28, wherein the method further comprises:

filtering the frequency shifted amplified signal to produce a filtered picture carrier signal;

applying phase adjustment to the filtered picture carrier signal to produce a phase-adjusted filtered picture carrier signal; and

processing the phase-adjusted filtered picture carrier signal to compensate for phase noise, to produce a phase control signal that is used to control the amount of the phase adjustment, and to generate the frequency shift feedback signal.

30. The method of claim 28, wherein the method further comprises:

receiving an input phase signal based on the frequency shifted amplified signal;

generating a phase error signal by comparing the input phase signal with a reference phase signal;

generating a frequency error signal based on the phase error signal;

summing the frequency error signal and a version of the phase error signal to produce an adjusted frequency error signal;

amplifying the phase adjusted frequency error signal to produce an amplified frequency error signal; and

generating the frequency shift feedback signal based on the amplified frequency error signal.

31. The method of claim 30, wherein generating the frequency shift feedback signal comprises:

updating a current frequency based on the amplified frequency error signal to produce a frequency adjusted signal;

limiting the frequency adjusted signal to an upper or lower limit when the frequency adjusted signal exceeds the upper or lower limit respectively; and

generating the frequency shift feedback signal based on the limited frequency adjusted signal.

32. The method of claim 29, wherein the method further comprises:

filtering the phase error signal to produce a filtered phase error signal; and

amplifying the filtered phase error signal to produce the version of the phase error signal.

33. The method of claim 25, wherein the method further comprises using a second frequency tracking loop to extract an audio carrier frequency of the desired television channel signal for analog television broadcast standards by applying a second known frequency shift to compensate for a known frequency offset in the audio carrier frequency.

34. The method of claim 33, wherein the method further comprises:

frequency shifting the frequency content of the processed digitized coarse channel signal to the baseband;

filtering the frequency shifted signal using an audio filtering stage to produce a filtered signal;

demodulating the filtered signal to produce a first intermediate audio signal; and

tracking the audio carrier signal that corresponds to the desired television channel signal based on one of the first intermediate audio signal and a sound IF carrier recovery signal and producing an audio frequency shift feedback signal used in the frequency shifting step.

35. The method of claim 28, wherein the method further comprises processing the shifted frequency content of the processed digitized coarse channel signal to extract an audio carrier frequency of the desired television channel signal for analog television broadcast standards, wherein the processing is based on the phase control signal.

36. The method of claim 28, wherein the method further comprises:

frequency shifting the shifted frequency content of the processed digitized coarse channel signal to the baseband;

filtering the frequency shifted signal using an audio filtering stage to produce a filtered signal;

demodulating the filtered signal to produce a first intermediate audio signal; and

tracking the audio carrier signal that corresponds to the desired television channel signal based on the first intermediate audio signal.