Fractional DSP Waveform Synthesis for Fixed-Rate DAC Baud Flexibility

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Solution Overview

Problem

Conventional signal sources for data communication applications face challenges in synthesizing waveforms for arbitrary baud rates, requiring time-consuming re-calibration and complex design with high-speed DACs that vary across a full octave in frequency, leading to sensitivity to sample rate changes.

Innovation Solution

The use of digital signal processing (DSP) to synthesize waveforms with an asynchronous or narrowly tunable rate DAC, employing fractional replication/interpolation techniques to up-sample waveforms to the desired baud rate, allowing dynamic changes in waveform baud rates without re-calibration and introducing impairments like jitter for stress testing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional synchronous waveform generation with variable sample rate DACs is used to support arbitrary baud rates, then adaptability to different baud rates is improved, but device complexity and calibration requirements increase

Engineering Contradiction:

Improvesupport for arbitrary baud ratesVSAvoidDAC design complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent changes the sample rate parameter from variable to fixed, decoupling the DAC sample rate from the baud rate. This allows the DAC to operate at a constant high sample rate while the baud rate varies arbitrarily, resolving the contradiction by making the sample rate parameter independent of the adaptive parameter (baud rate).

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an intermediary processing stage between the baud-rate signal and the fixed sample rate DAC. This intermediary performs resampling or interpolation to convert the variable baud rate signal to the fixed DAC sample rate, enabling arbitrary baud rate support without requiring the DAC itself to be variable.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If DAC sample rate is varied across full octave to support different baud rates, then adaptability is improved, but manufacturing precision and stability deteriorate due to sensitivity to sample rate changes

Engineering Contradiction:

Improvebaud rate flexibilityVSAvoidDAC performance stability

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent fixes the DAC sample rate parameter at a constant value, eliminating sample rate variations that cause manufacturing precision issues. The adaptability is achieved through digital signal processing rather than varying the DAC's fundamental operating parameter, thus maintaining manufacturing precision while achieving baud rate flexibility.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If conventional synchronous synthesis with integer interpolation is used, then device complexity is reduced, but adaptability to arbitrary baud rates deteriorates

Engineering Contradiction:

Improvesynthesis algorithm simplicityVSAvoidsupport for non-integer baud rate ratios

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent extends the simple integer interpolation approach to fractional interpolation, allowing the interpolation factor to be any rational number rather than just an integer. This maintains the simplicity of the synthesis algorithm while dramatically improving adaptability to arbitrary baud rates that may not have integer relationships with the sample rate.

Inventive Principle:

Principle #35Parameter changes

4Adaptability or versatility

If high-speed DACs with variable sample rate are designed, then adaptability to different baud rates is improved, but ease of manufacture and optimization deteriorate

Engineering Contradiction:

Improvebaud rate coverageVSAvoidDAC design and optimization

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent changes the DAC from a variable sample rate device to a fixed sample rate device operating at a consistently high rate. This simplifies the manufacturing and optimization process, as the DAC can be designed and tuned for a single operating point rather than requiring complex variable rate control circuits and multiple calibration modes.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11146280B2Digital signal processing waveform synthesis for fixed sample rate signal sources

Publication Date: 2021.10.12 TEKTRONIX INC

AI summary

A test and measurement instrument including a digital-to-analog converter having an output sample rate configured to receive a digital sample waveform and a reference clock and output an analog waveform at the sample rate, a waveform synthesizer configured to receive an input waveform having a baud rate and output a digital sample waveform having a baud rate less than the sample rate of the digital-to-analog converter, and a port configured to output the analog waveform.