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 resistor self-heating 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 an 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 a current DAC to adjust the R-2R ladder and account for temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an R-2R ladder DAC is used to achieve high voltage and high precision, then the output voltage range and precision are improved, but differential non-linearity errors occur due to resistor self-heating and temperature variations
Solution Approach 1:
The patent applies preliminary action by performing calibration procedures before actual DAC operation to determine correction coefficients. The system pre-characterizes the R-2R ladder resistors and stores correction data in lookup tables, so that when the DAC operates, the pre-computed trim codes immediately compensate for self-heating and temperature effects without requiring real-time complex calculations.
Solution Approach 2:
The patent implements feedback through calibration circuits that measure actual resistor behavior and generate correction coefficients based on observed deviations. The system uses feedback from calibration measurements to adjust the trim codes stored in memory, continuously improving compensation accuracy. The lookup tables are populated based on feedback from actual device characterization.
2Reliability
If resistor self-heating is compensated through calibration, then linearity accuracy is improved, but additional calibration circuits and trim codes are required
Solution Approach 1:
The patent reduces operational complexity by performing all complex calibration measurements and coefficient calculations during manufacturing or initial setup. The correction coefficients are pre-computed and stored in lookup tables within the DAC device, eliminating the need for complex real-time calculation hardware during normal operation. This shifts complexity from operational to setup phase.
Solution Approach 2:
The patent introduces lookup tables as an intermediary between the calibration process and the DAC operation. Instead of directly implementing complex self-heating compensation circuits, the system uses pre-stored trim codes from lookup tables to mediate the compensation process. This intermediary approach simplifies the operational circuitry while maintaining high accuracy.
3Measurement precision
If temperature coefficient mismatches are corrected, then precision across temperature variations is improved, but additional trim codes and calibration procedures are needed
Solution Approach 1:
The patent performs comprehensive temperature characterization during manufacturing, measuring resistor behavior across the full operating temperature range. Correction coefficients for temperature variations are pre-calculated and stored in the lookup tables, enabling the DAC to automatically compensate for temperature drift without requiring complex real-time temperature sensing or calculation circuits.
Solution Approach 2:
The patent addresses temperature coefficient mismatches by changing the effective resistance parameters through trim codes. The calibration process determines optimal trim code values that adjust the resistance parameters to compensate for temperature-induced variations. The lookup tables store these parameter adjustment values for different operating conditions.
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 by trimming the R-2R ladder and compensating for self-heating and temperature-related issues, enhancing the precision and accuracy of the analog output voltage across varying temperatures.
Implementation Method 1
a DAC that uses an 'R-2R' ladder is generally satisfactory for higher voltage and higher precision applications
Implementation Method 2
a value indicative of a product of a resistor temperature coefficient (TC) and a resistor self-heating coefficient (SHC)
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.