Compact DAC Current Reassignment for Monotonic Code Transitions
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Solution Overview
Problem
Existing digital-to-analog converters (DACs) face challenges in achieving monotonicity while minimizing the number of switches, which affects the size and accuracy of the converter.
Innovation Solution
A method for controlling a DAC that involves receiving a digital input, detecting changes in the most significant bits (MSBs) and least significant bits (LSBs), and using a switching circuit to decouple a current source from the LSB transconductance stage and couple it to the MSB transconductance stage, ensuring consistent current source error across transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a segmented DAC is used to reduce the number of switches, then device complexity is reduced, but monotonicity deteriorates
Solution Approach 1:
The patent implements dynamic switching of current sources based on the digital input code value. The system transitions from static current source allocation to dynamic allocation, where current sources are selectively enabled or disabled based on MSB/LSB transitions. This dynamic approach maintains monotonicity by ensuring proper current source switching during code transitions while keeping the physical number of switches limited.
Solution Approach 2:
The patent changes the operational parameters of the DAC by introducing switching control logic that monitors MSB and LSB transitions. When specific transition conditions are detected (MSB changes or LSB changes by 2^Y-1), the system adjusts which current sources are active. This parameter change approach allows the DAC to maintain monotonic behavior without requiring a full thermometric implementation with excessive switches.
2Reliability
If a thermometric DAC is used to ensure monotonicity, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent divides the DAC into distinct MSB and LSB sections with separate current source groups. Instead of using a single large thermometric array, the system segments the conversion function and applies different current source switching strategies to each segment. This segmentation allows monotonicity to be maintained through controlled transitions between segments rather than requiring a complete thermometric structure.
Solution Approach 2:
The patent makes current sources serve multiple functions by enabling them to be dynamically assigned to different operational modes. The same current source can serve the LSB section during normal operation and the MSB section during transition conditions. This multi-functionality reduces the total number of current sources and switches needed compared to a dedicated thermometric implementation.
3Area of stationary object
If the number of switches is reduced for compactness, then area is reduced, but manufacturing precision deteriorates
Solution Approach 1:
The patent implements preliminary detection of MSB and LSB transition conditions before actual current source switching occurs. The control logic anticipates when transitions will happen and prepares the switching state in advance. This preliminary action ensures that current sources are switched at the correct moment, maintaining linearity and monotonicity even with fewer switches and reduced area.
Data Source
AI summary
There is provided a method for controlling a digital-to-analog converter, DAC. The DAC receives a digital input comprising a plurality of bits including a first segment comprising X most significant bits, MSBs, and a second segment comprising Y least significant bits, LSBs. The DAC modifies the connection of a plurality of current sources, changing the current source coupling between LSB and MSB transconductance stages. By doing this, the monotonicity of the system can be improved in a compact DAC.