Method and system for direct digital up-conversion in a cable modem

• US 20050123029A1
• Filed: 10/28/2004
• Published: 06/09/2005
• Est. Priority Date: 12/03/2003
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chen, Chung-Ying, Vorenkamp, Pieter, Miller, Kevin L., Venes, Arnoldus G.
• Granted Patent: US 8,677,434 B2
• Time in Patent Office: Days
• US Class Current: 375/222
• CPC Class Codes: H04H 20/79 using downlink of the CATV systems, e.g. audio broadcast via CATV network
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

Provided are a method and system for a module for a cable modem termination system. The module includes a digital modulator configured to block up-convert a plurality of digital channels and a digital to analog converter coupled, at least indirectly, to an output of the digital modulator to convert the digital channels to an analog format.

Claims

1. A module for a cable modem termination system (CMTS), comprising:

a digital modulator configured to block up-convert a plurality of digital channels; and

a digital to analog converter (DAC) coupled, at least indirectly, to an output of the digital modulator to convert the digital channels to an analog format.

2. The method of claim 1, further comprising a serializer coupled between the digital modulator and the DAC.

3. The module of claim 2, wherein the digital modular include an interpolation filter and up-converter logic.

4. A module for performing block conversion in a cable modem termination system (CMTS), comprising:

a digital modulator configured to up-convert one or more digital channels; and

a digital to analog converter (DAC) configured to transform the up-converted channels from digital domain to an analog domain.

5. The module of claim 4, wherein the module is a digital up-converter.

6. The module of claim 4, wherein the channels are adjacent to one another.

7. The module of claim 5, wherein each of the channels includes a quadrature amplitude modulated (QAM) carrier signal.

8. The module of claim 4, wherein the digital modulator includes an interpolation filter and up-conversion logic.

9. The module of claim 4, further comprising a serializer to serialize an output from the modulator and provide a serialized signal as an input to the DAC.

10. The module of claim 4, wherein the digital modulator and the DAC are formed on a single integrated circuit (IC).

11. The module of claim 10, wherein the digital modulator and the DAC are based upon a clock speed greater than or equal to two giga-samples per second.

12. The module of claim 4, wherein the DAC is a 12 bit DAC.

13. The module of claim 4, wherein the module includes built-in testability.

14. The module of claim 13, further comprising a direct digital frequency synthesizer configurable for being multiplexed with the up-converted digital channels and being provided as an input, at least indirectly, to the DAC.

15. The module of claim 4, further comprising a switching device configured to selectively provide one of a primary clock signal and a secondary clock signal as an input to at least the DAC.

16. The module of claim 4, further comprising a clock generator for synchronizing operation of the modulator, the DAC, the serializer to operation of base-band devices.

17. An up-conversion system for a cable modem termination system (CMTS), comprising:

a combiner for combing one or more digital channels into a single bit-stream stream;

a digital modulator to modulate the digital bit-stream; and

a digital to analog converter (DAC) for converting the digital bit-stream into one or more analog radio frequency output signals.

18. The up-conversion system of claim 17, wherein the combiner is of the heterodyne variety.

19. The up-conversion system of claim 17, wherein the digital modulator and the DAC are formed on a first single integrated circuit (IC);

and wherein the combiner is formed on a second IC.

20. The up-conversion system of claim 18, wherein the digital modulator, the DAC, and the combiner are formed on a single IC.

21. A method for testing a block up-converting module within a cable modem termination system (CMTS), the module including a digital modulator coupled to a digital to analog converter (DAC), the method comprising:

multiplexing one or more fixed input words with an output of the digital modulator to produce a multiplexed signal; and

providing the multiplexed signal, at least indirectly, as an input to the DAC.

22. The method of claim 21, further comprising analyzing an output of the DAC when the multiplexed signal is provided as an input thereto.

23. The method of claim 22, wherein the fixed input words are representative of two or more independent frequencies.

24. The method of claim 23, wherein the two or more independent frequencies are produced in accordance with direct digital frequency synthesis principles.

25. The method of claim 21, wherein the multiplexing and the providing occur while the DAC is operating at speed.