Self-Calibrating DAC Circuit for Differential Nonlinearity
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Solution Overview
Problem
Digital-to-analog converters (DACs) face inaccuracies due to manufacturing errors, leading to differential non-linearity (DNL) issues, particularly when transitioning between control codes, which current calibration methods fail to adequately address.
Innovation Solution
A self-calibrating DAC system utilizing a tunable cell, weighted cells, and a calibration cell, enabled by a calibration sequence and signal, adjusts the tunable cell's weight to minimize errors through sampling and processing of analog output differences, effectively reducing DNL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a DAC uses fixed-weight current cells, then the device complexity is low, but the manufacturing precision deteriorates due to process variations causing DNL errors
Solution Approach 1:
The patent applies dynamics by making the current cell weights adjustable rather than fixed. Each current cell is replaced with a tunable current cell whose weight can be dynamically adjusted during calibration to compensate for manufacturing variations. This allows the DAC to adapt its weight values to achieve accurate DNL performance despite process variations.
Solution Approach 2:
The patent changes the weight parameters of current cells from fixed to tunable. By introducing tuning words and calibration circuits, the weight values can be modified to compensate for manufacturing errors. The calibration process adjusts these parameters to minimize DNL, transforming a static design into one with adjustable parameters for improved precision.
2Manufacturing precision
If a DAC incorporates calibration circuits and tunable cells, then the manufacturing precision improves, but the device complexity increases
Solution Approach 1:
The patent implements self-service through automatic calibration functionality. The calibration circuit automatically adjusts the tuning words of tunable current cells to minimize DNL errors without requiring external manual intervention. The system self-calibrates by measuring output accuracy and adjusting weights accordingly, reducing the need for complex external calibration equipment and manual procedures.
Solution Approach 2:
The patent employs feedback mechanisms where the calibration circuit monitors the DAC output and uses this information to adjust the tuning words of current cells. The feedback loop continuously optimizes the weight values to maintain accurate DNL performance, allowing the system to automatically correct for manufacturing variations through iterative adjustment based on measured performance.
3Measurement precision
If the DAC operates in calibration mode with all cells enabled, then the measurement precision improves, but the productivity decreases due to calibration time
Solution Approach 1:
The patent applies periodic action by implementing calibration at specific intervals rather than continuously. The DAC operates in normal conversion mode during most time, periodically switching to calibration mode to adjust tuning words. This periodic calibration approach maintains measurement precision while minimizing the impact on productivity, as calibration is performed only when needed rather than continuously interfering with normal operation.
Solution Approach 2:
The patent implements preliminary action by performing calibration before normal operation or during initialization. The tuning words are adjusted in advance to establish accurate weight values, and then the DAC operates in normal mode without continuous calibration interference. This preliminary calibration ensures measurement precision is established beforehand, allowing high-speed conversion operations to proceed without repeated calibration interruptions.
Data Source
AI summary
A digital-to-analog converter improves differential non-linearity by performing a calibration of at least one weighted cell in response to a calibration command. The digital-to-analog converter includes a group of weighted cells, a tunable cell having a tunable weight controlled by a tuning word, and a calibration cell to generate a combined output signal in response to a digital input word, the calibration command, and a calibration sequence. The digital-to-analog converter also includes a calibration circuit configured to sample and subsequently process the combined output signal to establish the tuning word in accordance with the calibration command and the calibration sequence.