DAC Output-Node Calibration for Current Switch Mismatch
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Solution Overview
Problem
High-speed and high-resolution digital-to-analog converters (DACs) face performance issues due to current source switch element mismatch, which existing calibration methods at the source node fail to fully address, as they do not account for parasitic effects and weighting network inaccuracies.
Innovation Solution
A DAC calibration system that measures and corrects current source switch element mismatch at the output node by using a multiplexer, current switches, weighting networks, and calibration modules to generate orthogonal digital signals, convert output currents to pulses, and adjust bias voltages based on measured voltage or current values to ensure matching output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If source node current measurement is used for calibration, then calibration process is simplified, but measurement accuracy deteriorates because it does not reflect the actual mismatch at the output node
Solution Approach 1:
The patent introduces an intermediary measurement approach by using the output node as the measurement point instead of the source node. A calibration signal is injected at the output node and propagated backward through the weighting network to the current source switches, allowing accurate measurement of the actual output current mismatch while maintaining a systematic calibration process.
2Measurement precision
If output node current measurement is used for calibration, then measurement accuracy improves, but device complexity increases due to the need for additional calibration circuits and orthogonal signaling
Solution Approach 1:
The patent employs periodic action by using orthogonal calibration signals that are injected in a systematic sequence. The calibration process uses periodic switching of the multiplexer to apply calibration signals to different current source switches in turn, allowing the system to measure and correct each switch's contribution to output mismatch through repeated cyclic measurement and adjustment.
Solution Approach 2:
The calibration system is segmented into modular functional blocks: a multiplexer for signal routing, individual calibration signal injection circuits for each current source switch, a measurement circuit at the output node, and a control unit for coordinating the calibration process. This segmentation allows the complex calibration function to be implemented through manageable, independent modules.
3Productivity
If high speed and high resolution are achieved in DAC design, then performance improves, but current source switch element mismatch worsens due to manufacturing variations and parasitic effects
Solution Approach 1:
The patent implements feedback by measuring the actual output current at the DAC output node and using this measurement to adjust and correct the current source switch elements. The calibration process continuously monitors the output current contribution of each switch and applies corrective adjustments to compensate for manufacturing variations and parasitic effects, ensuring accurate current matching despite high-speed operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively measures and corrects current source switch element mismatch at the output node, ensuring linear output voltage and current, thereby improving the accuracy and linearity of high-speed and high-resolution DACs.
Implementation Method 1
a resistive element coupled between the output node and a ground source, conducting the total output current pulse to the ground source to produce an output voltage on the output node
Data Source
AI summary
The present invention relates generally to a digital-to-analog converter (DAC) calibration. The present invention may be implemented by a DAC calibration system including a first current source, a first switch coupled to the first current source, a second current source, a second switch coupled to the second current source, an output node coupled to the first switch and the second switch, a first calibration module coupled to the output node, an average current measurement module coupled to the first calibration module, and a second calibration module coupled to the average current measurement module.