Digital implementation of multi-channel demodulators

Details Digital implementation of multi-channel demodulators Digital implementation of multi-channel demodulators

2001-09-18

2004-03-09

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Receivers

C375S347000

Reexamination Certificate

active

06704372

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
NOT APPLICABLE
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
NOT APPLICABLE
REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.
NOT APPLICABLE
BACKGROUND OF THE INVENTION
The present invention relates generally to broadband communications, and more particularly to a method and circuitry for implementing demodulator circuits.
There is a growing acceptance of video services, such as video on demand, and an anticipated deployment of home servers. As a result, broadband appliance manufacturers have an increasing need to support multiple simultaneous channels of digital content delivered over the cable system. This need includes other systems such as satellite and terrestrial TV systems. The ability to simultaneously demodulate potentially all of the channels viewed by a particular home can fundamentally change the viewing paradigm for video content from one that is driven by network schedules to one that is driven by consumers independent of networks.
FIG. 1
is a simplified high-level block diagram of a traditional multi-channel cable and satellite demodulator
100
of a type that is used in cable and satellite systems. A multi-channel RF input signal typically includes a plurality of RF channels, each characterized by a different carrier frequency and being modulated in accordance with desired information to be carried on that channel. Each channel's bandwidth is less than the spacing of the carrier frequencies. For example, carrier frequencies in the UHF band (300 MHz to 3 GHz) may be spaced at 6 MHz intervals. Included are receiver chains
102
a
,
102
b
, and
102
c
. Each chain includes a tuner
110
, an analog-to-digital converter (ADC)
120
and a digital demodulator
130
. Digital demodulator
130
includes a forward error correction (FEC) circuit (not explicitly shown).
The function of each tuner
110
is to select an RF channel falling within a specific frequency band. There is one tuner for each RF channel. The input RF signal for a tuner contains many or all RF channels. Each tuner then converts the frequency of its selected RF channel to a lower fixed frequency pass band for cable systems, or to baseband for satellite systems. Each ADC
120
then digitizes the selected RF signal. Then each digital demodulator
130
performs signal demodulation and outputs recovered digital bits with error indication signals.
Each RF channel requires one analog tuner and analog band-pass or low-pass filters. The problem with this approach is that the cost, power consumption, and complexity go up as the required number of RF channels goes up.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method and circuitry for demodulating signals such as downstream signals. At least some embodiments are characterized by lower cost, lower power consumption, and/or lower complexity.
A digital multi-channel demodulator circuit according to an embodiment of the invention includes a frequency-block down-converter that receives a multi-channel analog RF signal and shifts the multi-channel analog RF signal to a lower frequency band. An ADC receives the multi-channel analog RF signal from the frequency-block down-converter and converts the multi-channel analog RF signal to a multi-channel digital RF signal. A digital channel demultiplexer receives the multi-channel digital RF signal from the ADC and demultiplexes the multi-channel digital RF signal into separate digital RF channels.
Other embodiments include a digital selector that receives the separate RF channels and selects one or more RF channels, and a plurality of demodulators that receive one or more of the RF channels from the digital selector and demodulate one or more of the RF channels.
Other embodiments include a digital tuner for use in multi-channel demodulation. The digital tuner includes a numeric control oscillator (NCO) that generates a select frequency, the select frequency being associated with a corresponding and separate RF channel. A complex multiplier receives the multi-channel digital RF signal and multiplies the multi-channel digital RF signal with the select frequency and passes the result through a low-pass filter LPF to extract the signal that is superimposed on the corresponding RF channel.
Other embodiments include a polyphase channel demultiplexer for use in multi-channel demodulation. The polyphase channel demultiplexer includes at least one low-pass filter (LPF) configured to receive the multi-channel digital RF signal and to synchronize the RF channels. Also included is a discrete Fourier transform circuit (DFT) that demultiplexes the multi-channel digital RF signal into separate digital RF channels.
Embodiments of the present invention achieve their purposes and benefits in the context of known circuit and process technology and known techniques in the electronic and process arts. Further understanding, however, of the nature, features, and advantages of the present invention is realized by reference to the latter portions of the specification, accompanying drawings, and appended claims.


REFERENCES:
patent: 5299192 (1994-03-01), Guo et al.
patent: 5504783 (1996-04-01), Tomisato et al.
patent: 5699363 (1997-12-01), Wishart et al.
patent: 6014366 (2000-01-01), Ichiyoshi
patent: 6263195 (2001-07-01), Niu et al.
patent: 000296175 (1988-12-01), None

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