Multi-channel receiver with improved AGC
View Patent ↗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.
1. A receiver comprising:
a gain section adapted to generate, based on a gain control value, an output signal from two or more differently-modulated 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 the two or more differently-modulated received signals;
the receiver comprises two or more demodulators and two or more scalars corresponding to the two or more differently-modulated 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 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.
5. A method for processing two or more differently-modulated received signals, the method comprising:
generating, based on a gain control value, an output signal from the two or more differently-modulated 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.
6. The method of claim 5 , wherein:
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.
7. The method of claim 6 , 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.
8. The method of claim 5 , further comprising the step of digitizing the output signal for generating the intensity value and for each demodulation of the output signal.
9. Apparatus for processing two or more differently-modulated received signals, the apparatus comprising:
means for generating, based on a gain control value, an output signal from the two or more differently-modulated 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.
10. The apparatus of claim 9 , wherein:
the apparatus is adapted to process three received signals comprising a COFDM signal and two TDM signals; and
the apparatus comprises means for demodulating the COFDM signal, means for demodulating the two TDM signals, and means for scaling the three received signals.
11. The apparatus of claim 9 , wherein the means for generating and adaptively updating the gain control value and each scalar control value, responsive to the means for demodulating, is adapted to independently delay the change of each scalar control value in accordance with any differences in the processing delays by the means for demodulating.