Auxiliary Current Sources for Waveform Synthesis SFDR
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Solution Overview
Problem
Existing digital waveform synthesizers face limitations in spurious-free dynamic range (SFDR) due to limited output impedance of current sources, causing deviations from ideal sine waveforms as the number of activated current cells increases.
Innovation Solution
The use of auxiliary current sources weighted according to a predefined waveform, such as sine squared, in parallel with main current sources, to compensate for code-dependent variations in main current outputs, thereby maintaining accurate waveform synthesis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of activated current cells is increased to improve waveform accuracy, then the output current of each current cell decreases due to limited output impedance, causing deviation from ideal sine waveform
Solution Approach 1:
The patent implements feedback by measuring the actual output current of each current cell and using this information to adjust the activation state of auxiliary current sources. This closed-loop control compensates for the current reduction caused by limited output impedance, maintaining stable and accurate current output even when multiple cells are activated simultaneously.
Solution Approach 2:
The patent changes the operational parameters by introducing auxiliary current sources that can be dynamically activated or deactivated based on the number of active main current cells. This parameter adjustment compensates for the non-ideal behavior of current sources, maintaining constant output current regardless of the total number of activated cells.
2Manufacturing precision
If auxiliary current sources are added to compensate for main current variations, then waveform accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the current source function into two distinct parts: main current sources that generate the primary waveform signal and auxiliary current sources that provide compensation. This segmentation allows each type of current source to have a specialized function, improving overall waveform accuracy while organizing the complexity into manageable, functionally-separated components.
Solution Approach 2:
The auxiliary current sources are designed to serve multiple purposes: they compensate for the limited output impedance of main current sources, correct for non-ideal current distribution, and maintain waveform accuracy across different operating conditions. This multi-functionality justifies the added complexity by providing multiple benefits from a single component addition.
Data Source
AI summary
A circuit is provided with a plurality current cells. The current cells each comprise a main current source and an auxiliary current source coupled in parallel. The main current source supplies a main current to a current output of the current cell, and the auxiliary current source supplies an auxiliary current to the current output of the current cell. The main current sources are weighted according to a first predefined waveform, and the auxiliary current sources are weighted according to a second predefined waveform which is different from the first predefined waveform.