Multi-channel receiver with improved AGC

• US 20080159446A1
• Filed: 12/29/2006
• Published: 07/03/2008
• Est. Priority Date: 12/29/2006
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Wang, Zhenyu, Yu, Jinguo, Lai, Yhean-Sen, Song, Jie
• Granted Patent: US 7,978,773 B2
• Time in Patent Office: Days
• US Class Current: 375/345
• CPC Class Codes: H03G 3/3068 Circuits generating control signals for both R.F. and I.F. stages
• CPC Class Codes: H03G 3/3078 Circuits generating control signals for digitally modulated signals
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/2649 Demodulators

Abstract

An improved multi-channel receiver for satellite broadcast applications or the like. In an exemplary embodiment, a primary AGC loop controls an analog sub-receiver adapted to simultaneously receive multiple signals. Multiple digital demodulators, coupled to the sub-receiver, demodulate the multiple received signals. Multiple secondary AGC loops, one for each received signal, compensate for variations in demodulated signal strengths caused by the primary AGC loop. A feed-forward AGC compensation technique generates scalar control values for scaling the demodulated signals before the demodulated signals are processed by the secondary AGC loops. This at least partially compensates for gain variations caused by the primary AGC, reducing received signal drop-outs before the secondary AGC loops can compensate for the gain variations. Because of systemic delays in the sub-receiver and the demodulators, the scalar control values are independently timed to be coincident with the variations in the demodulated signal strengths caused by the primary AGC loop.

Claims

1. A receiver comprising:

a gain section adapted to generate, based on a gain control value, an output signal from one or more received signals;

a detector adapted to generate an intensity value in response to the output signal;

a demodulator, for each received signal, adapted to demodulate the output signal into a corresponding demodulated signal having an amplitude;

a scalar, for each demodulated signal, adapted to scale the amplitude of the corresponding demodulated signal based on a corresponding scalar control value; and

a controller adapted to generate and adaptively change the gain control value and each scalar control value based on changes in the intensity value, wherein the controller is further adapted to delay a change of at least one of the scalar control values based on at least one processing delay associated with generating the corresponding demodulated signal.

2. The receiver of claim 1, wherein:

the receiver is adapted to receive two or more received signals;

the receiver comprises two or more demodulators and two or more scalars corresponding to the two or more received signals; and

the controller is adapted to delay the change of each scalar control value based on the at least one processing delay associated with the generation of the corresponding demodulated signal.

3. The receiver of claim 2, wherein the controller, responsive to the two or more demodulators, is adapted to independently delay the change of each scalar control value in accordance with any differences in the processing delays by the demodulators.

4. The receiver of claim 3, wherein the controller is adapted to delay the change of each scalar control value to coincide in time with a change in the corresponding demodulated signal resulting from an earlier change in the intensity value.

5. The receiver of claim 1, wherein:

the receiver is adapted to process three received signals comprising a COFDM signal and two TDM signals; and

the receiver comprises a COFDM demodulator, two TDM demodulators, and three scalars corresponding to the three received signals.

6. The receiver of claim 1, wherein the controller is adapted to delay the change of the at least one scalar control value to coincide in time with a change in the corresponding demodulated signal resulting from an earlier detected change in the intensity value.

7. The receiver of claim 1, further comprising an analog-to-digital converter adapted to digitize the output signal for application to the detector and each demodulator, wherein:

the detector is a power detector;

each demodulator is a digital down-converter; and

the power detector, each demodulator, each scalar, and the controller are implemented in a digital processor.

8. The receiver of claim 1, wherein the controller is adapted to control a change in gain of each scalar to be substantially equal and opposite to a earlier change in gain of the gain section, such that amplitude scaling by each scalar at least partially compensates for gain changes by the gain section.

9. The receiver of claim 1, further comprising a secondary gain loop for each scaled, demodulated signal generated by the corresponding scalar.

10. The receiver of claim 9, wherein each secondary gain loop comprises:

a secondary scalar adapted to further scale the corresponding scaled, demodulated signal based on a secondary scalar control value; and

a secondary detector adapted to generate the secondary scalar control value based on the output of the secondary scalar.

11. A method for processing one or more received signals, the method comprising:

generating, based on a gain control value, an output signal from the one or more received signals;

generating an intensity value in response to the output signal;

demodulating, for each received signal, the output signal into a corresponding demodulated signal having an amplitude;

scaling, for each demodulated signal, the amplitude of the corresponding demodulated signal based on a corresponding scalar control value; and

generating and adaptively updating the gain control value and each scalar control value based on changes in the intensity value, wherein a change of at least one scalar control value is delayed based on at least one processing delay associated with generating the corresponding demodulated signal.

12. The method of claim 11, wherein:

the output signal is generated, based on the gain control value, from two or more received signals; and

the change of each scalar control value is delayed based on the at least one processing delay associated with the generation of the corresponding demodulated signal.

13. The method of claim 12, wherein:

the output signal is generated, based on the gain control value, from three received signals comprising a COFDM signal and two TDM signals; and

the output signal is independently demodulated by a COFDM demodulator and two TDM demodulators.

14. The method of claim 12, wherein the change of each scalar control value is independently delayed to take into account any differences in the processing delays associated with the generation of the two or more demodulated signals.

15. The method of claim 14, wherein the change of each scalar control value is delayed to coincide in time with a change in the corresponding demodulated signal resulting from an earlier detected change in the intensity value.

16. The method of claim 11, wherein the change of the at least one scalar control value is delayed to coincide in time with a change in the corresponding demodulated signal resulting from an earlier detected change in the intensity value.

17. The method of claim 11, further comprising the step of digitizing the output signal for generating the intensity value and for each demodulation of the output signal.

18. The method of claim 11, wherein a change in gain of each scalar is controlled to be substantially equal and opposite to an earlier change in gain of the gain section, such that amplitude scaling of each demodulated signal at least partially compensates for changes in gain in generating the output signal.

19. The method of claim 11, further comprising the step of further scaling each scaled, demodulated signal based on a corresponding secondary scalar control value generated based on the further scaled, demodulated signal.

20. Apparatus for processing one or more received signals, the apparatus comprising:

means for generating, based on a gain control value, an output signal from the one or more received signals;

means for generating an intensity value in response to the output signal;

means for demodulating, for each received signal, the output signal into a corresponding demodulated signal having an amplitude;

means for scaling, for each demodulated signal, the amplitude of the corresponding demodulated signal based on a corresponding scalar control value; and

means for generating and adaptively updating the gain control value and each scalar control value based on changes in the intensity value, wherein a change of at least one scalar control value is delayed based on at least one processing delay associated with generating the corresponding demodulated signal.