Current-Steering DAC Common-Mode Correction for Stable Output
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Solution Overview
Problem
Current digital-to-analog converters (DACs) in wireless communication systems face challenges with non-constant common-mode (CM) current, which affects signal quality and noise levels due to the dependency of CM current on the DAC input code, particularly when a bypass path is implemented.
Innovation Solution
A current-steering DAC system with a bypass path is developed, incorporating a common-mode current compensation path that generates a compensation current to reduce the CM current component, directing it between the positive and negative output paths, thereby maintaining a constant net CM current independent of the input code.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bypass path is implemented in the DAC to improve signal routing flexibility, then the DAC can handle different input code ranges more efficiently, but the common-mode current becomes non-constant and dependent on the input code
Solution Approach 1:
A common-mode current compensation path is introduced as an intermediary element between the positive and negative output paths. This compensation path includes a compensation current source that generates a current equal to the difference between the positive and negative output currents, thereby canceling out the non-constant common-mode current component and restoring stability to the overall common-mode current.
Solution Approach 2:
The compensation current source dynamically adjusts its output current based on the input code by selectively activating compensation current sources corresponding to bypassed most significant bits. This parameter change allows the compensation path to counteract the varying common-mode current produced by the bypass path across different input code ranges.
2Productivity
If the DAC uses a current-steering architecture with bypass paths, then conversion speed and efficiency are improved, but noise interference increases due to varying CM current
Solution Approach 1:
The compensation path acts as an intermediary that isolates the harmful varying common-mode current generated by the current-steering bypass architecture from affecting the output signal quality. By injecting the compensation current into the common-mode path, the harmful noise component is canceled while preserving the beneficial fast conversion performance of the current-steering architecture.
3Measurement precision
If the DAC maintains high precision across all input codes, then signal accuracy is improved, but the complexity of maintaining constant CM current increases
Solution Approach 1:
The compensation current source is segmented into multiple individual compensation current sources, each corresponding to a specific most significant bit that can be bypassed. This segmentation allows the system to activate only the necessary compensation components based on the input code, maintaining precision while managing complexity through modular design rather than requiring a fully complex continuous compensation mechanism.
Data Source
AI summary
Certain aspects of the present disclosure are directed to a digital-to-analog converter (DAC) system. The DAC system generally includes a first current-steering DAC having a positive output, a negative output, and a bypass output; a common-mode (CM) path coupled between the positive and negative outputs; and a CM current compensation path coupled to the CM path.