Current-Steering DAC Scrambling for Lower Harmonic Distortion

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional current-steering digital-to-analog converters (DACs) face challenges in achieving high accuracy and speed due to statistical variations in switches, leading to errors in current output, which result in degradation of linear performance and increased harmonic distortion.

Innovation Solution

A scrambling system is introduced for the DAC, which includes a scrambling module that randomly selects current sources based on the digital input word, using binary-thermometer row and column decoders to generate control signals and pseudo-random sequences, thereby eliminating the correlation of errors with the output signal and reducing harmonic distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional current-steering DAC architecture is used, then the DAC can achieve high speed operation, but statistical variations in switches cause errors in current output leading to degradation of linear performance and increased harmonic distortion

Engineering Contradiction:

Improveoperation speedVSAvoidlinear performance

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent applies dithering technique that intentionally introduces random noise into the digital input signal to randomize the switching patterns. This converts the harmful effect of statistical variations into a beneficial averaging effect where the errors become uncorrelated with the output signal, thereby reducing harmonic distortion and improving linear performance while maintaining high-speed operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Measurement precision

If high resolution (12-14 bit) and high speed (above 100 MHz) are pursued, then the DAC meets modern communication requirements, but statistical variations in switches lead to increased harmonic distortion

Engineering Contradiction:

Improveconversion accuracyVSAvoidharmonic distortion

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent introduces dithering that adds controlled random noise to the digital input, which randomizes the switching behavior of the current sources. This converts the harmful correlated errors generated by statistical variations into uncorrelated noise, significantly reducing harmonic distortion and spurious-free dynamic range degradation while enabling high-resolution high-speed conversion

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent modifies the digital input signal parameters by adding a dither component with specific statistical properties (random noise). This parameter change transforms the deterministic switching patterns into stochastic patterns, causing the errors to average out over time and reducing their impact on the analog output spectrum

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7586429B1Scrambling system for high resolution ditigal-to-analog converter

Publication Date: 2009.09.08 MARVELL ASIA PTE LTD

AI summary

A scrambling system for a digital-to-analog converter (DAC) includes a DAC that receives a digital input word and a scrambling module that randomly selects at least one of a plurality of current sources based on the digital input word. The DAC outputs an analog signal based on the at least one of the plurality of current sources.