Current-Steering DAC Calibration Using Reused R2R Mismatch Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current digital-to-analog converters (DACs), particularly current-steering DACs, face challenges in accurately measuring current source mismatches, which can lead to inaccuracies in converting input digital signals to analog outputs due to variations in current generation among the sources.
Innovation Solution
The implementation of a measurement circuit within the DAC that includes a first set of current sources, a resistive network, and a measurement circuit to compare currents generated by a second set of current sources against a reference current, using a current combining circuit to quantify mismatches and adjust control signals to calibrate the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current-steering DAC uses multiple current sources to generate analog output, then the conversion capability is enhanced, but current source mismatches cause measurement and calibration inaccuracies
Solution Approach 1:
The patent segments the measurement process into distinct phases: isolating individual current sources using switching circuits, measuring each current source separately against a reference, and combining results. This segmentation allows accurate measurement of each current source's mismatch without interference from others, resolving the contradiction between multi-source capability and measurement precision.
Solution Approach 2:
The patent introduces an intermediary measurement circuit that includes a reference current source and switching elements. This intermediary circuit mediates between the multiple current sources and the measurement process, enabling accurate comparison of each current source against a stable reference while maintaining the overall system's conversion capability.
2Adaptability or versatility
If external measurement equipment is used to measure current mismatches, then measurement flexibility is improved, but device complexity and calibration difficulty increase
Solution Approach 1:
The patent implements a universal measurement circuit that can measure all current sources within the DAC using the same integrated circuitry. The measurement circuit serves multiple functions: it can measure any current source by switching, provide reference currents, and generate calibration data. This multi-functionality eliminates the need for external equipment while maintaining measurement flexibility and reducing overall system complexity.
Solution Approach 2:
The DAC performs self-measurement and self-calibration through its own integrated measurement circuit. The system uses its internal resources (current sources, switching circuits, reference voltages) to measure and calibrate itself, eliminating dependency on external measurement equipment and reducing system complexity while maintaining flexibility.
3Productivity
If the R2R network is used for both DAC operation and current measurement, then component utilization is improved, but measurement accuracy may be affected by network loading
Solution Approach 1:
The patent employs preliminary action by switching the R2R network into a high-impedance state during measurement phases, preventing loading effects before they can occur. The measurement circuit is designed to isolate the R2R network from measurement currents, ensuring that the network's dual use for both DAC operation and measurement does not compromise accuracy.
Solution Approach 2:
The patent makes the R2R network dynamic by switching it between different operational states: active for DAC conversion and high-impedance/isolated for measurement. This dynamic reconfiguration allows the network to serve both functions without loading effects degrading measurement precision, as the network's state adapts to the current operational requirement.
Data Source
AI summary
A current digital-to-analog converter includes a binary current-generating section configured to generate a binary-weighted current based on a first set of control signals; a unary current-generating section configured to generate a unary-weighted current based on a second set of control signals; and a current combining circuit configured to add or subtract a reference current and a current generated by a current source of the unary current-generating section using the binary-weighted current.