Parallel Sub-Band Signal Generator for High-Speed Optical Links
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Solution Overview
Problem
Current high-speed signal generators are limited by the sample rate of digital-to-analog converters (DACs), which restricts the maximum bit-rate of optical communication systems to around 10 Gb/s, as they can only generate frequency components up to half of their sample rate, necessitating the development of higher-speed signal sources to support increasing spectral widths.
Innovation Solution
A method involving a digital signal processor generating parallel digital sub-band signals, each processed by a DAC to produce analog sub-band signals, which are then combined using a RF mixing and summation circuit to generate an output signal with frequency components up to twice the sample rate, effectively extending the spectral range from DC to NFs/2, suitable for high-bit rate optical communication systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a DAC with sample rate Fs is used to generate analog drive signals, then the system can operate with simpler converter hardware, but the maximum frequency components are limited to Fs/2, restricting the bit-rate to around 10 Gb/s
Solution Approach 1:
The patent divides the digital drive signal into multiple parallel sub-band signals (e.g., low-band and high-band) that can be processed by separate DACs operating at lower sample rates. Each sub-band is then up-converted to different frequency ranges using mixers, allowing the overall system to achieve higher effective bandwidth without requiring a single high-speed DAC. This segmentation resolves the contradiction by breaking down the high-speed requirement into manageable lower-speed parallel processing stages.
Solution Approach 2:
The patent transitions from a single-dimensional time-domain signal processing approach to a multi-dimensional approach by introducing frequency domain processing through parallel sub-band decomposition and up-conversion. By adding the frequency dimension through spectral splitting and selective up-conversion, the system extends the effective bandwidth beyond the limitation of a single DAC's Nyquist frequency, thereby achieving higher bit-rates without proportionally increasing DAC speed requirements.
2Speed
If the DAC sample rate is increased to extend the frequency spectrum beyond Fs/2, then higher bit-rates can be achieved, but the cost and complexity of the DAC hardware increase significantly
Solution Approach 1:
The patent changes the operating parameters of multiple DACs from a single high sample rate to multiple lower sample rates. By processing the signal in parallel sub-bands and up-converting each to different frequency ranges, the system achieves an effective spectral width of NFs/2 (where N is the number of sub-bands) using DACs with sample rate Fs, rather than requiring a single DAC with sample rate NFs. This parameter transformation resolves the contradiction by achieving high spectral width through architectural configuration rather than hardware speed escalation.
3Productivity
If a single high-speed DAC is used to generate wideband signals, then the device architecture remains simple, but the maximum transmission symbol rates are limited to around 10 Gb/s
Solution Approach 1:
The patent segments the wideband signal generation task into multiple parallel channels, each handling a specific frequency sub-band. By dividing the digital drive signal into low-band and high-band components and processing them through separate DAC-mixer chains, the system achieves higher overall transmission symbol rates. Each parallel channel operates at manageable speeds while the combined output delivers the high-speed performance needed for 100 Gb/s and beyond, resolving the contradiction between productivity and complexity through functional decomposition.
Solution Approach 2:
The patent merges multiple parallel signal processing chains (each consisting of a DAC and up-conversion mixer) into a single composite output signal. By combining the up-converted sub-band signals from multiple parallel channels, the system achieves high transmission symbol rates that exceed what any single channel could provide alone. This merging strategy resolves the contradiction by aggregating the capabilities of multiple lower-complexity channels to achieve high productivity.
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 enables the generation of high-speed analog signals with spectral content from DC to NFs/2, doubling the maximum transmission symbol rates and supporting higher modulation formats, such as M-ary PSK and QAM, in optical communication systems beyond the limitations of existing technologies.
Implementation Method 1
A digital signal processing (DSP) block generates a set of N (where N is an integer and N≥2) parallel digital sub-band signals, each digital sub-band signal having frequency components within a spectral range between 0 Hz and ±Fs/2
Implementation Method 2
A respective Digital-to-Analog Converter (DAC) processes each digital sub-band signal to generate a corresponding analog sub-band signal, each DAC having a sample rate of Fs
Implementation Method 3
A combiner combines the analog sub-band signals to generate an output analog signal having frequency components within a spectral range between 0 Hz and ±NFs/2
Data Source
AI summary
A high speed signal generator comprises a digital signal processing (DSP) block configured to process an input digital signal to generate in parallel a first digital sub-band signal having frequency components within a first spectral range and a second digital sub-band signal having frequency components within the first spectral range. A first Digital-to-Analog Converter (DAC) is configured to process the first digital sub-band signal to generate a first analog sub-band signal and a second DAC is configured to process the second digital sub-band signal to generate a second analog sub-band signal. A combiner is to combine the first analog sub-band signal and the second analog sub-band signal to generate an output analog signal having frequency components covering a substantially continuous spectral range from a lower frequency f1 to a higher frequency f2. The substantially continuous spectral range is substantially wider than a width of the first spectral range, and the lower frequency f1 is less than or equal to one-third of the higher frequency f2.