Pulse width modulator for communication system including fiber optic communications

• US 6,457,178 B1
• Filed: 03/17/1998
• Issued: 09/24/2002
• Est. Priority Date: 03/17/1998
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Slim, David H.
• Primary Examiner(s): Faile, Andrew
• Assistant Examiner(s): Koenig, Andrew Y.
• Application Number:
  US09/040,008
• Time in Patent Office: 1,652 Days
• Field of Search: H04/N.7173, H04/N.716, H04/J 1.402, H04/B 1.004, 725/127, 725/129, 725/118, 725/119, 725/149, 359/125, 359/184, 359/186, 375/238, 332/109, 332/110
• US Class Current: 725/127
• CPC Class Codes: H04B 10/25751 Optical arrangements for CATV or video distribution adaptations of television systems for optical transmission H04N7/22
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/524 Pulse modulation
• CPC Class Codes: H04N 21/615 Signal processing at physical level signal processing in analog two-way television systems H04N7/173
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications
• CPC Class Codes: H04N 7/22 Adaptations for optical transmission

Abstract

A cable television system (100) includes ahead end section (105) for processing information provided from subscriber equipment via a reverse path within the system (100). The reverse signal is provided from subscriber equipment in the form of a broadband RF signal, which can include voice, data, and/or video information. The broadband RF signal is provided from a plurality of subscribers to a node (200) that pulse width modulates the RF signal to generate a reverse optical signal. The pulse width modulated optical signal is then provided to the head end section (105) for processing to recover the information contained therein.

Claims

1. A communication system for processing forward and reverse signals, the communication system comprising:

a node for converting a reverse broadband radio frequency (RF) signal to a reverse optical signal using pulse width modulation of an optical source, wherein the optical source that generates the reverse optical signal having pulses of durations that are proportional to amplitudes of the reverse broadband RF signal, the node comprising;

a sampling circuit for sampling the reverse broadband RF signal to generate a sampled signal;

a linear sweep generator for generating a ramp waveform;

a comparator for comparing the ramp waveform and the sampled signal and for generating an output signal when the ramp waveform is equal to the sampled signal;

logic for terminating generation of the ramp waveform by the linear sweep generator in response to reception of the output signal from the comparator; and

a pulse generator for driving the optical source based upon duration of the ramp waveform.

2. The communication system of claim 1, further comprising:

a head end section for generating a forward optical signal; and

a converter for converting the forward optical signal into a plurality of forward RF signals for transmission to subscribers of the communication system.

3. The communication system of claim 1, wherein the optical source comprises a laser diode.

4. The communication system of claim 2, further comprising:

a photoelectric detector for receiving the reverse optical signal and recovering therefrom the reverse broadband RF signal, wherein the reverse broadband RF signal is further processed by the head end section to recover information encoded therein.

5. A cable television system, comprising:

a head end section for transmitting a forward optical signal;

a converter for converting the forward optical signal to a plurality of forward RF signals for transmission over branches of the cable television system;

taps located along the branches of the cable television system for routing portions of the plurality of forward RF signals to subscriber equipment;

a node for receiving a reverse broadband RF signal from the subscriber equipment and for pulse width modulating the reverse broadband RF signal via an optical source to generate a reverse optical signal for transmission to the head end section, the node comprising;

a sampling circuit for sampling the reverse broadband RF signal to generate a sampled signal;

a linear sweep generator for generating a ramp waveform;

a comparator for comparing the ramp waveform and the sampled signal and for generating an output signal when the ramp waveform is equal to the sampled signal;

logic for terminating generation of the ramp waveform by the linear sweep generator in response to reception of the output signal from the comparator; and

a pulse generator for driving the optical source based upon duration of the ramp waveform.

6. The cable television system of claim 5, wherein the converter is included within the node.

7. The cable television system of claim 5, wherein the reverse broadband RF signal includes video information.

8. The cable television system of claim 5, wherein the reverse broadband RF signal includes data information.

9. The cable television system of claim 5, wherein the reverse broadband RF signal includes voice information.

10. The cable television system of claim 5, wherein the node comprises:

the optical source for generating the reverse optical signal, which is characterized by pulses having durations that are proportional to amplitudes of the reverse broadband RF signal.

11. The cable television system of claim 5, wherein the optical source comprises a laser diode.

12. The cable television system of claim 5, further comprising:

a photoelectric detector for receiving the reverse optical signal and recovering therefrom the reverse broadband RF signal, wherein the reverse broadband RF signal is further processed by the head end section to recover information encoded therein.