Segmented DAC Thermometer Tuning for INL Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital-to-analog converter (DAC) devices suffer from integral non-linearity (INL) issues, particularly in high-speed wireline applications, which are not adequately addressed by current calibration methods targeting random mismatches, leading to performance degradation.
Innovation Solution
A system and method that adjusts the relative strength of thermometer segments in DAC devices to minimize INL by comparing actual output with an ideal linear output, using a calibration circuit and processor to iteratively tune each segment to achieve zero INL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermometer encoding is used in DAC segments, then mismatch impacts are reduced, but systematic INL remains unaddressed
Solution Approach 1:
The patent applies preliminary action by performing calibration of thermometer segments before actual DAC operation. The calibration process pre-adjusts the strength of each thermometer segment to compensate for systematic errors, ensuring that when the DAC operates normally, both random mismatch and systematic INL are minimized. This is achieved by sequentially calibrating each segment against a reference DAC that provides ideal linear output values.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the strength parameter of each thermometer segment during calibration. By varying the signal strength of individual segments and comparing outputs against a reference, the system identifies and corrects systematic deviations. This parameter adjustment continues iteratively until the thermometer segments produce linear output characteristics, thereby resolving the systematic INL issue while maintaining the mismatch reduction benefits of thermometer encoding.
2Reliability
If calibration is performed to reduce random mismatches, then mismatch effects are minimized, but systematic INL is not corrected
Solution Approach 1:
The patent applies segmentation by dividing the DAC into multiple thermometer segments and calibrating each segment independently. Rather than treating the DAC as a single unit, the calibration process sequentially adjusts each thermometer segment's strength based on its individual performance relative to a reference DAC. This segmented approach allows systematic INL errors in each segment to be identified and corrected separately, while maintaining the overall benefits of thermometer encoding for reducing random mismatch.
3Speed
If differential drivers are used for high-speed transmission, then data transport speed increases, but 3rd order non-linearity is introduced
Solution Approach 1:
The patent implements feedback by using a reference DAC to generate ideal linear output values that are continuously compared against the actual DAC output during calibration. The comparison circuit detects deviations between the ideal and actual outputs, and this feedback information is used to adjust the thermometer segment strengths. This feedback mechanism enables the system to compensate for the 3rd order non-linearity introduced by differential drivers, allowing high-speed transmission to proceed with minimized distortion.
Data Source
AI summary
A system and method for compensating segmented DAC intrinsic INL by adjusting the relative strength of DAC thermometer segments. In the method, the strength of each thermometer segment is adjusted sequentially to reduce INL to 0 at one point on each thermometer code range. The strength of the binary section is also adjusted to further reduce INL while conserving output amplitude. The system includes a calibration circuit that senses the DAC differential output and compares it to an ideal output generated from the same DAC via dithering between 0 and a maximum code. The compensation scheme only performs a specific type of DAC compensation, specifically compensating for systematic non-linearity rather than for mismatch-induced non-linearity. The method can also be applied to calibrate a full thermometer DAC.