Digital optical receiver for cable television systems

• US 6,433,906 B1
• Filed: 09/22/1999
• Issued: 08/13/2002
• Est. Priority Date: 09/22/1999
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Farhan, Forrest M.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US09/401,477
• Time in Patent Office: 1,056 Days
• Field of Search: 359/167, 359/115, 359/118, 359/123, 359/124, 359/137, 359/189, 359/162, 725/121, 725/124, 725/129, 375/229, 375/350, 375/232
• US Class Current: 398/167.5
• CPC Class Codes: H04B 10/27 Arrangements for networking
• CPC Class Codes: H04N 7/22 Adaptations for optical transmission

Abstract

A cable television system (400) includes a transmitter (200) for generating a digital optical signal and a receiver (201) for receiving such digital optical signal and converting it to an analog signal. The receiver (201) includes a digital filter (300) disposed between a deserializer (225) and a digital-to-analog converter (230), which digital filter conditions the digital electrical signal received from the deserializer (225). 1o The digital filter (300) is employed as a digital noise mitigation block so as to improve the quality of the signals in the reverse path, returning to the cable television system (400) headend (105).

Claims

1. In a communications system including an optical transmitter for transmitting digital optical signals via a communications medium to an optical receiver, the optical receiver comprising:

a detector for receiving a digital optical signal and for converting said digital optical signal to a serial stream of electrical pulses;

a serial-to-parallel converter for converting said serial stream of electrical pulses to a set of parallel outputs corresponding to a digital word;

a first digital filter coupled to said serial-to-parallel converter and adapted to filter said digital word,

wherein said first digital filter comprises at least one bandpass filter, and wherein the at least one bandpass filter is adapted to filter a different spectral portion of said digital word;

a second digital filter coupled to said first digital filter, said second digital filter adapted to filter said filtered digital word,

wherein said second digital filter comprises at least one adaptive estimation filter, and wherein each adaptive estimation filter is coupled to each bandpass filter; and

a digital to analog converter coupled to the second digital filter for converting the filtered digital word to an analog electrical signal.

2. An optical receiver as in claim 1, wherein said receiver is disposed in the headend of a cable television system.

3. An optical receiver as in claim 1, wherein said receiver is disposed in a hub deployed in a cable television system.

4. The communications system of claim 1, wherein said first digital filter comprises a plurality of bandpass filters.

5. The communications system of claim 4, wherein said second digital filter comprises a plurality of adaptive estimation filters.

6. A cable television system for providing signals, the cable television system comprising:

an optical transmitter for receiving an analog information signal and transmitting in accordance therewith a digital optical signal representative of the analog information signal;

an optical receiver for receiving the digital optical signal via a communication medium and receiving therefrom an analog signal representative of the analog information signal, said optical receiver including a converter for converting said digital optical signal to a digital electrical signal, and a digital filter for filtering said digital electrical signal according to at least one criteria,

the digital filter comprising;

a first digital filter adapted to filter a different spectral portion of the digital electrical signal; and

a second digital filter coupled to the first digital filter, wherein the second digital filter is an adaptive estimation filter,

whereby combining the first and second digital filters reject out-of-band and in-band interference.

7. A cable television system as in claim 6, wherein said first digital filter compromises a plurality of bandpass filters.

8. A cable television system as in claim 7, wherein said second digital filter comprise s a pluraity of adaptive estimation filters.