Current-Steering DAC Calibration for Static Linearity Correction
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Solution Overview
Problem
High-resolution digital to analog converters face limitations in performance due to current source matching, with existing calibration methods being costly in terms of production time, silicon area, and design complexity, and failing to effectively calibrate both binary and thermometric combinations.
Innovation Solution
A method for static linearity calibration of current steering DACs using a minimal analog hardware feedback loop, comprising a comparator, digital mismatch estimator, and compensator, which estimates and compensates errors in current sources through a calibration DAC, reducing silicon area and design complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lookup memory is used to store measured mismatch data and apply error voltage during normal operation, then current source accuracy is improved, but production time increases and silicon area increases due to on-chip memory
Solution Approach 1:
The patent extracts the mismatch correction function from a separate lookup memory table and integrates it directly into the DAC structure. The correction values are embedded within the existing current source architecture, eliminating the need for external or large on-chip memory while maintaining accuracy improvement.
Solution Approach 2:
The patent makes the DAC structure multi-functional by enabling it to perform both normal conversion and mismatch correction simultaneously. The same current sources and switching network are used for both the primary DAC function and the correction function, eliminating dedicated correction hardware and reducing silicon area.
2Measurement precision
If lookup memory is used to store measured mismatch data and apply error voltage during normal operation, then current source accuracy is improved, but production time increases
Solution Approach 1:
The patent performs mismatch measurement and correction value generation as a preliminary step during manufacturing, but the correction is applied automatically during normal operation without requiring additional production time. The correction values are pre-calculated and integrated into the device structure, allowing immediate application during use.
3Measurement precision
If gate voltage of MOS current sources is adjusted by changing reference current values to ensure matching, then current source matching is improved, but design complexity increases due to plurality of switches
Solution Approach 1:
The patent merges the correction function with the existing DAC structure by using the same current sources and switching network for both primary conversion and correction. This integration eliminates the need for separate correction switches and reduces design complexity while maintaining matching accuracy.
4Measurement precision
If fixed reference current source and two sub DAC setup are used to estimate error and change gate voltage, then current source error correction is improved, but silicon area and power increase
Solution Approach 1:
The patent makes the DAC structure multi-functional by enabling it to perform both normal conversion and mismatch correction simultaneously. The same current sources and switching network are used for both the primary DAC function and the correction function, eliminating dedicated correction hardware and reducing silicon area.
Solution Approach 2:
The patent merges the correction function with the existing DAC structure by using the same current sources and switching network for both primary conversion and correction. This integration eliminates the need for separate correction hardware and reduces both silicon area and power consumption.
5Measurement precision
If R2R DAC is used to estimate error at output node, then current source mismatch calibration is improved, but applicability is limited to equal current sources only
Solution Approach 1:
The patent changes the fundamental approach from using an R2R DAC (which assumes equal current steps) to a method that works with binary-weighted and thermometric combinations. The correction mechanism is adapted to handle different current source configurations by using programmable correction values that match the specific DAC architecture being used.
Data Source
AI summary
In accordance with the present invention a system and method for calibration of the current steering DAC is elaborated which helps to reduce design complexity and reduce silicon area required in the design. Present invention is utilising a clocked comparator and plurality of switch transistors 405,305 and AUX DAC in conjunction with digital estimator and digital compensator blocks to estimate the errors in the current sources 406 and compensate the errors using same AUX DAC during normal operation mode.