Digital Up-Conversion Module for Cable Modem Signal Interference
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Solution Overview
Problem
Conventional cable modem systems face challenges with signal interference and distortion due to analog components, and testing high-speed digital to analog converters is difficult without specialized measures.
Innovation Solution
A digital up-conversion module that block up-converts multiple channels in the digital domain, using a digital modulator and a 12-bit digital to analog converter (DAC) on a single integrated circuit, with built-in test capabilities enabled by a direct digital frequency synthesizer for testing high-speed operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If analog components (mixers, filters, amplifiers) are used in conventional CMTS transmitters to modulate and up-convert base-band signals, then the system can transmit multiple channels in the frequency range from 50 MHz to 860 MHz, but signal interference and distortion occur due to the analog phase lock loop generating multiple signals
Solution Approach 1:
The patent replaces the analog phase lock loop system with a digital phase lock loop system. The digital PLL generates a single clock signal that is then used to generate all necessary local oscillator frequencies through digital signal processing, eliminating the multiple analog clock sources that caused signal interference and distortion while maintaining the capability to transmit multiple channels.
2Manufacturing precision
If a 12-bit digital to analog converter (DAC) operates at clock frequencies in excess of 2 giga-samples per second to achieve high performance level, then the conversion precision and speed are improved, but testing becomes virtually impossible without special test measures and procedures
Solution Approach 1:
The patent incorporates built-in self-test (BIST) functionality directly into the DAC and up-converter system. Test patterns are generated and applied to the DAC at its normal high operating speed (exceeding 2 giga-samples per second), allowing the system to test itself under actual operating conditions without requiring external specialized test equipment or slowing down the converter.
3Adaptability or versatility
If multiple clock sources or a single tunable source are used in the analog phase lock loop to generate local oscillator frequencies for up-conversion, then the system can cover the required frequency range, but multiple signals are created that contribute to signal interference
Solution Approach 1:
The patent merges multiple separate clock generation functions into a single digital phase lock loop system. One master clock source generates the timing signal, which is then processed digitally to produce all necessary local oscillator frequencies for up-converting multiple channels. This consolidation eliminates the multiple analog signals that caused interference while maintaining full frequency range coverage from 50 MHz to 860 MHz.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces signal interference, optimizes power consumption, and allows for effective testing of high-speed components, enhancing the performance and testability of cable modem systems.
Implementation Method 1
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
Data Source
AI summary
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.