Segmented DEM DAC Architecture for ISI and Mismatch Suppression
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Solution Overview
Problem
Digital-to-analog converters (DACs) face distortion due to non-ideal circuit behavior, particularly element mismatches and nonlinear inter-symbol interference (ISI), which affect the accuracy of multi-bit DAC outputs.
Innovation Solution
A high linearity digital-to-analog converter design employing segmentation and dynamic element matching techniques, using a combination of multi-bit DEM DACs with different DEM techniques such as rotated PWM and DWA algorithms, to reduce distortion and ISI errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple 1-bit DACs are used in thermometer coding multi-bit DAC designs, then the DAC can convert digital input to analog output, but element mismatches occur during fabrication causing error in the multi-bit DAC output
Solution Approach 1:
The multi-bit digital input is segmented into multiple code segments, with each segment driving a separate multi-bit DEM DAC. This segmentation allows different DEM techniques to be applied to different segments, enabling targeted correction of element mismatches in specific portions of the DAC output.
Solution Approach 2:
Different DEM techniques (such as rotated PWM and DWA algorithms) are applied to different code segments based on their specific characteristics. This parameter change approach allows optimization of each segment's element matching independently, improving overall DAC accuracy while addressing fabrication variations.
2Reliability
If practical 1-bit DACs are used, then the DAC can operate with real circuit behavior, but non-instantaneous transitions between levels introduce signal-dependent transient errors containing ISI
Solution Approach 1:
Dynamic Element Matching techniques are employed that adaptively adjust element selection based on signal transitions and prior input bit values. The DEM circuit dynamically compensates for transient errors by selecting optimal DAC elements during transitions, reducing ISI while maintaining reliable operation.
Solution Approach 2:
The DEM circuit uses feedback from prior input bit values and current transition states to adjust element selection in real-time. This feedback mechanism allows the system to compensate for signal-dependent transient errors and reduce ISI without sacrificing operational reliability.
3Measurement precision
If the same DEM technique is used for all code segments, then the design is simpler, but distortion caused by DAC nonlinearity cannot be sufficiently reduced
Solution Approach 1:
The DAC is divided into multiple independent code segment processing paths, each capable of using different DEM techniques. This segmentation enables sophisticated nonlinearity correction without requiring a single complex DEM circuit, distributing the complexity across multiple simpler parallel paths.
Solution Approach 2:
Different DEM techniques are selectively applied to different code segments based on their specific nonlinearity characteristics. This local quality approach allows optimization of each segment's distortion performance with the most appropriate technique, achieving high overall precision without uniformly complex design.
4Measurement precision
If instantaneous switching between levels is achieved, then transient errors are eliminated, but non-ideal circuit behavior makes this impossible in practice
Solution Approach 1:
Instead of attempting to eliminate the inherent non-instantaneous transitions that are unavoidable in practical circuits, the DEM technique converts this harmful effect into a manageable characteristic by dynamically compensating for it. The finite transition time becomes a known parameter that can be corrected through adaptive element selection.
Solution Approach 2:
The DEM circuit acts as an intermediary between the digital input and the physical DAC elements, mediating the transition process by selecting optimal elements based on transition state. This intermediary layer provides the ideal instantaneous switching behavior at the system level despite non-ideal individual component behavior.
Data Source
AI summary
A digital-to-analog conversion circuit is used for converting a first digital input into a first analog output, and includes a segmentation circuit, a plurality of multi-bit dynamic element matching digital-to-analog converters (DEM DACs), and a combination circuit. The segmentation circuit applies segmentation to the first digital input to generate a plurality of code segments. The multi-bit DEM DACs convert the code segments into a plurality of DAC outputs, respectively, wherein the multi-bit DEM DACs include at least a first multi-bit DEM DAC and a second multi-bit DEM DAC, and the first multi-bit DEM DAC and the second multi-bit DEM DAC employ different DEM techniques. The combination circuit combines the DAC outputs to generate the first analog output.