Multi-Bit DAC Element Selection to Suppress Repeated-Data Tones
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Solution Overview
Problem
Multi-bit delta-sigma data converters experience tone generation due to mismatched current sources in the internal multi-bit DAC, leading to noise that is not effectively dispersed, particularly when specific data are repeatedly inputted, which can decrease the signal-to-noise ratio (SNR) and affect resolution.
Innovation Solution
A dynamic elements matching circuit using data weight averaging (DWA) technique that dynamically selects unit elements based on input data and adjusts the pointer position and circulation direction to prevent tone generation by averaging mismatching errors and dispersing noise into a wider band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multi-bit delta-sigma modulator and internal multi-bit DAC are used, then stability of the whole system is increased and high SNR is achieved with relatively low oversampling ratio, but noise is generated due to mismatched current sources in the internal multi-bit DAC
Solution Approach 1:
The patent applies dynamic element matching (DEM) technique that dynamically switches between multiple current sources based on input data patterns. Instead of using fixed current sources, the system dynamically selects and combines different current sources to generate the required output current, thereby distributing and averaging the mismatch errors across multiple sources over time. This dynamic switching mechanism prevents tone generation while maintaining system stability and achieving high SNR with low oversampling ratio.
Solution Approach 2:
The patent changes the operational parameters of the DAC by varying the selection and combination of current sources based on input data characteristics. When specific data patterns are detected (indicating potential tone generation), the system alters which current sources are activated and how they are combined. This parameter change strategy redistributes the mismatch errors dynamically, converting correlated noise into uncorrelated noise that appears as white noise rather than tones, thus reducing audible noise while maintaining high fidelity.
2Manufacturing precision
If conventional DWA technique is used to select unit elements, then mismatching errors are averaged, but tone generation occurs when specific data are repeatedly inputted
Solution Approach 1:
The patent incorporates a feedback mechanism that monitors the input data patterns and detects when specific data are repeatedly inputted. Based on this feedback, the system dynamically adjusts the element selection strategy to prevent tone generation. The feedback loop identifies correlated noise patterns and modifies the DWA technique accordingly, switching between different current sources or altering the switching sequence to break the correlation, thereby converting tones into white noise while maintaining error averaging benefits.
Solution Approach 2:
The patent enhances the conventional DWA technique by making it dynamic and adaptive. Instead of following a fixed switching sequence, the system dynamically adjusts which unit elements are selected based on real-time detection of input data patterns. When repeated data patterns are detected, the system dynamically changes the selection strategy to prevent tone generation. This dynamic adaptation allows the system to maintain mismatching error averaging under normal conditions while preventing tone generation when specific data patterns occur.
Data Source
AI summary
A method for converting data includes matching dynamic elements by repeatedly selecting a portion of unit elements among N unit elements according to data and a circulation direction. An existence of a tone generation possibility is determined by comparing a present pointer position with a previous pointer position and by comparing present data with previous data. At least one of the present pointer position and the circulation direction is changed based on the existence of the tone generation possibility. The present pointer position and the present data are stored or the changed pointer position and the present data are stored. Unit elements are sequentially selected by the present data from the stored pointer position in the circulation direction or the changed circulation direction. The present pointer position is moved by the present data in the circulation direction or the changed circulation direction.