Multi-Bit DAC Cell Swapping for Continuous Active Calibration
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Solution Overview
Problem
Existing calibration methods for multi-bit digital-to-analog converters (DACs) in high-speed and high-resolution analog-to-digital converters (ADCs) fail to account for charge injected by switching means during normal operation, leading to inaccuracies in calibration and reduced linearity.
Innovation Solution
An additional DAC cell is provided to be interchangeable with other DAC cells, allowing for active calibration without interrupting conversion, enabling measurement and compensation of both DC and dynamic mismatches through a calibration circuit that uses each DAC cell as a 1-bit ADC, simulating normal operation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switching means are inactive during calibration in known methods, then calibration can be performed, but charge injection effects during normal operation are not accounted for leading to calibration inaccuracies
Solution Approach 1:
The calibration method transitions from a static approach (switching means inactive) to a dynamic approach (switching means active) by performing calibration while the switching means are in their normal operational state, thereby capturing charge injection effects and improving both calibration accuracy and linearity
Solution Approach 2:
The system uses feedback from the calibration process to adjust and compensate for charge injection effects. By measuring the actual charge injection during active switching and feeding this information back into the calibration algorithm, the system achieves higher accuracy while maintaining reliability
2Measurement precision
If calibration is performed by taking DAC cells out of service, then calibration can be completed, but conversion process is interrupted
Solution Approach 1:
The DAC is segmented into multiple cells, allowing one cell to be calibrated while others remain in service. This segmentation enables calibration to be performed on individual cells without taking the entire DAC out of operation, maintaining conversion continuity
Solution Approach 2:
The calibration process is designed to occur continuously in the background while the DAC remains operational. By using redundant cells and performing calibration during normal operation rather than requiring shutdown, the useful action of conversion continues uninterrupted
3Measurement precision
If additional DAC cell is added for active calibration, then calibration accuracy improves, but device complexity increases
Solution Approach 1:
The additional DAC cell serves multiple functions: it acts as a spare cell that can replace any failed cell, and simultaneously serves as a calibration reference cell. This multi-functionality justifies the added complexity by providing both redundancy and improved calibration capability
Solution Approach 2:
The system changes the operational parameters of the additional cell dynamically - it can be switched between being a standby replacement cell and an active calibration reference cell depending on system needs. This parameter flexibility allows the cell to serve multiple purposes without permanently increasing functional complexity
Data Source
AI summary
In a method for calibrating a multi-bit DAC intended, particularly, for application in high-speed and high-resolution ADCs, such as ΣΔ ADCs, and comprising a number of DAC cells, apart from the number of DAC cells applied in the multi-bit DAC for conversion, an additional DAC cell is provided, which can be interchanged with each of the other DAC cells in order to switch each DAC cell successively from the multi-bit DAC into a calibration circuit to calibrate said DAC cell without interrupting the conversion. The calibration circuit includes means for measuring errors in the DAC cell under calibration and means for correcting said DAC cell.