Carrier recovery processor for a QAM television signal

• US 5,315,619 A
• Filed: 05/15/1992
• Issued: 05/24/1994
• Est. Priority Date: 05/15/1992
• Status: Expired due to Term

• Current Assignee: RCA Thomson Licensing Corporation
• Original Assignee: RCA Thomson Licensing Corporation
• Inventors: Bhatt, Bhavesh B.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US07/883,735
• Time in Patent Office: 739 Days
• Field of Search: 375/39, 375/88, 375/94, 358/141, 358/13, 358/181, 370/20, 370/77, 370/100.1
• US Class Current: 375/340
• CPC Class Codes: H03M 13/25 Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM] modulation codes H03M13/31
• CPC Class Codes: H04L 27/3872 Compensation for phase rotation in the demodulated signal
• CPC Class Codes: H04N 11/30 with transmission of the extra information by means of quadrature modulation
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 9/44 Colour synchronisation
• CPC Class Codes: H04N 9/66 for synchronous demodulators

Abstract

A television receiver responds to a quadrature amplitude modulated (QAM) signal containing symbols mapped into a four quadrant grid-like constellation defined by I and Q axes. Demodulated I and Q components are processed by a carrier recovery network which adjusts the parameters of a locally generated carrier reference signal so as to maintain a desired orientation of the QAM constellation. The carrier recovery network includes a time multiplexed processor, including a signal multiplier, exhibiting plural operating modes in a digital phase locked loop exhibiting a loop delay of one symbol period.

Claims

1. In a television signal receiver including a signal processing path for processing a television signal containing a carrier quadrature amplitude modulated (QAM) with symbols exhibiting a given symbol period and mapped into prescribed locations of a grid-like constellation, apparatus comprising:

means for generating a reference signal nominally at the frequency of said carrier;

input means responsive to said modulated carrier and to said reference signal for producing a processed modulated carrier;

means for generating a control signal as a function of an offset exhibited by a constellation associated with said processed carrier relative to a constellation associated with said television signal; and

means for coupling said control signal to said signal processing path for reducing said offset;

wherein

said means for generating said control signal is a time multiplexed processor with plural operating modes providing a product-type output signal in at least one of said plural operating modes representative of said offset.

2. Apparatus according to claim 1, wherein

said multiplexed processor exhibits a complete multiplex operating cycle within said symbol period.

4. Apparatus according to claim 1, wherein

said television signal exhibits a spectrum wherein said quadrature amplitude modulated carrier is modulated with high priority information relative to information modulating an additional carrier in said spectrum.

5. Apparatus according to claim 1, wherein

said multiplexer processor comprises a signal multiplier.

3. In a television signal receiver including a signal processing path for processing a television signal containing a carrier quadrature amplitude modulated (QAM) with symbols exhibiting a given symbol period and mapped into prescribed locations of a grid-like constellation, apparatus comprising:

means for generating a reference signal nominally at the frequency of said carrier;

input means responsive to said modulated carrier and to said reference signal for producing a processed modulated carrier;

means for generating a control signal as a function of an offset exhibited by a constellation associated with said processed carrier relative to a constellation associated with said television signal; and

means for coupling said control signal to said signal processing path for reducing said offset;

wherein

said means for generating said control signal is a time multiplexed processor with plural operating modes providing a product-type output signal in at least one of said plural operating modes representative of said offset, said multiplexed processor being responsive to a first signal containing a constellation of symbols at received locations, and to a second signal containing a constellation of symbols at expected locations, said output signal of said multiplexed means representing a difference between said received and expected locations.

6. In a television signal receiver including a signal processing path for processing a television signal containing a carrier quadrature amplitude modulated (QAM) with symbols exhibiting a given symbol period and mapped into prescribed locations of a grid-like constellation, apparatus comprising:

means for generating a reference signal nominally at the frequency of said carrier;

input means responsive to said modulated carrier and to said reference signal for producing a processed modulated carrier;

means for generating a control signal as a function of an offset exhibited by a constellation associated with said processed carrier relative to a constellation associated with said television signal; and

means for coupling said control signal to said signal processing path for reducing said offset;

wherein

said means for generating said control signal is a time multiplexed processor with plural operating modes providing a product-type output signal in at least one of said plural operating modes representative of said offset; and

said multiplexed processor comprises a signal multiplier which is multiplexed with latch means to successively perform multiplying and accumulating functions.

7. In a television signal receiver including a signal processing path for processing a television signal containing a carrier quadrature amplitude modulated (QAM) with symbols exhibiting a given symbol period and mapped into prescribed locations of a grid-like constellation, apparatus comprising:

means for generating a reference signal nominally at the frequency of said carrier but subject to exhibiting a phase or frequency offset with respect to said carrier;

input means responsive to said modulated carrier and to said reference signal for producing a processed modulated carrier;

means for generating a control signal as a function of said offset, said means for generating said control signal including a phase locked loop comprising multiplier means providing an output signal as a function of said offset in response to a first signal with symbols at received locations and to a second signal with symbols at expected locations;

means for providing timing signals to said phase locked loop for causing said phase locked loop including said multiplier means to exhibit time-multiplexed operation; and

means for coupling said control signal to said signal processing path for reducing said offset.

8. Apparatus according to claim 7, wherein

said phase locked loop including said multiplier means exhibits a complete multiplex operating cycle within said symbol period.

9. Apparatus according to claim 7, wherein

said control signal adjusts the phase of said reference signal.

10. Apparatus according to claim 7, wherein

said television signal exhibits a spectrum including said quadrature amplitude modulated carrier modulated with high priority information relative to information modulating an additional carrier in said spectrum;

and

said phase locked loop including said multiplier means exhibits a complete multiplex operating cycle within said symbol period.

11. Apparatus according to claim 10, wherein

said input means comprises an adaptive equalizer.

12. Apparatus according to claim 7, wherein

said phase locked loop is a second order phase locked loop.

13. In a television signal receiver including a signal processing path for processing a television signal containing a carrier quadrature amplitude modulated (QAM) with symbols exhibiting a given symbol period and mapped into prescribed locations of a grid-like constellation, apparatus comprising:

means for generating a reference signal nominally at the frequency of said carrier but subject to exhibiting a phase of frequency offset with respect to said carrier;

input means responsive to said modulated carrier and to said reference signal for producing a processed modulated carrier;

means for generating a control signal as a function of said offset, said generating means including a second order phase locked loop comprising multiplier means providing an output signal as a function of said offset in response to a first signal with symbols at received locations and to a second signal with symbols at expected locations;

means for providing timing signal to said phase locked loop for causing said phase locked loop including said multiplier means to exhibit time-multiplexed operation; and

means for coupling said control signal to said signal processing path for reducing said offset, wherein said phase locked loop includes

means responsive to said processed modulated carrier for selecting said symbols, said selecting means exhibiting a first signal gain factor and including memory means for generating said second signal with said symbols at expected locations.

14. Apparatus according to claim 13 and further including

means in said phase locked loop exhibiting a second signal gain factor.