R-2R Ladder DAC Calibration for Self-Heating Linearity Errors
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Solution Overview
Problem
Digital-to-analog converters (DACs) face challenges in achieving high precision and large output voltage ranges due to differential non-linearity (DNL) errors caused by self-heating of resistors and temperature-related mismatches in R-2R ladder architectures, which affect the accuracy of analog signal conversion.
Innovation Solution
An integrated circuit with a DAC core using a thermometric R-2R ladder, a DNL calibration circuit, a self-heating calibration circuit, and a temperature calibration circuit that generates trim codes to correct for DNL and self-heating errors, utilizing memory-stored resistor temperature coefficients and self-heating coefficients to adjust the R-2R ladder, thereby improving the accuracy of analog signal conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an R-2R ladder DAC is used for high voltage and high precision applications, then the output voltage range and precision are improved, but differential non-linearity errors occur due to self-heating of resistors and temperature-related mismatches
Solution Approach 1:
The patent applies preliminary action by performing calibration procedures before actual DAC operation to determine and store correction values for self-heating and temperature effects. The calibration circuits pre-characterize the resistor temperature coefficients and self-heating coefficients, storing these values in memory for later compensation during normal operation, thus preventing DNL errors before they occur.
Solution Approach 2:
The patent implements feedback through calibration circuits that measure the actual performance of the R-2R ladder and generate correction values based on observed self-heating and temperature drift. These correction values are fed back to adjust the DAC output, creating a closed-loop system that continuously compensates for thermal effects and maintains precision despite temperature variations.
2Reliability
If resistor self-heating is compensated for, then DNL error is reduced, but additional calibration circuits and memory are required
Solution Approach 1:
The patent merges the self-heating calibration functionality with the existing R-2R ladder structure by using the same resistor network for both normal operation and calibration measurements. The calibration circuits share common nodes and components with the operational DAC, reducing overall device complexity while still providing comprehensive self-heating compensation.
3Measurement precision
If temperature coefficient calibration is performed, then temperature-related mismatches are corrected, but the calibration process becomes more complex
Solution Approach 1:
The patent applies parameter changes by measuring and storing the temperature coefficients of the resistors at different temperatures during calibration. These temperature-dependent parameters are captured and used to generate correction values that adapt to varying operating conditions, enabling the DAC to maintain precision across a wide temperature range through programmed compensation.
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 solution effectively reduces DNL and integral non-linearity errors, enhancing the precision and reliability of the DAC's analog output by trimming the R-2R ladder and compensating for self-heating and temperature-related drift, ensuring accurate conversion across varying conditions.
Implementation Method 1
a self-heating calibration circuit generates a self-heating trim code based on the value from the memory
Implementation Method 2
a DAC core to convert a DAC code to an analog signal including a plurality of thermometric arms and an R-2R ladder
Data Source
AI summary
An integrated circuit includes a digital-to-analog converter (DAC) core including a plurality of thermometric arms and an R-2R ladder, the DAC core to convert a DAC code to an analog signal. The integrated circuit includes additional components as well. A differential non-linearity (DNL) calibration circuit outputs DNL coefficients based on the DAC code. A memory stores a value indicative of a product of a resistor temperature coefficient (TC) and a resistor self-heating coefficient (SHC). A current DAC (IDAC) couples to the R-2R ladder. A self-heating calibration circuit generates a self-heating trim code based on the value from the memory. An adder adds a value indicative of the DNL coefficients with the self-heating trim code to generate an IDAC trim code and provides the IDAC trim code to the IDAC to trim the R-2R ladder.