DAC Dummy Cell Architecture for Supply-Induced Linearity Errors
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Solution Overview
Problem
The linearity of capacitive Digital-to-Analog Converters (DACs) is limited by the finite impedance of the reference power supply, leading to harmonic distortions due to the modulation of the supply voltage by the supply current, which affects the output waveform.
Innovation Solution
The proposed solution involves a DAC architecture with a plurality of first and second DAC cells, where the second DAC cells are driven by dummy data to decorrelate the supply current from the first digital data, thereby reducing the impedance of the power supply and minimizing harmonic distortions. This is achieved by generating dummy data that opposes or complements the first digital data, ensuring the supply current is independent of the input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dummy switching is applied to decorrelate supply current from digital data, then linearity is improved and harmonic distortions are reduced, but device complexity increases due to additional DAC cells and dummy data generation circuitry
Solution Approach 1:
The DAC is segmented into first DAC cells for normal operation and second dummy DAC cells for decorrelation. This segmentation allows the supply current to be decoupled from the digital input data by having the dummy cells switch independently, thereby improving linearity without affecting the primary conversion function.
Solution Approach 2:
Dummy DAC cells act as an intermediary element that mediates between the power supply and the digital input data. By introducing these dummy cells that switch based on dummy data, the harmful correlation between supply current and input data is broken, improving linearity while the dummy cells themselves serve as the intermediate mechanism.
2Object-generated harmful factors
If dummy DAC cells are added to reduce supply current correlation, then harmonic distortions are reduced, but the number of components increases
Solution Approach 1:
The dummy DAC cells convert the harmful effect of supply current correlation into a benefit. By intentionally adding switching activity from dummy cells, the original harmful correlation between supply current and digital data is counteracted, transforming the power supply interaction from harmful to beneficial for linearity.
Solution Approach 2:
The switching behavior parameter of the DAC is changed by introducing dummy cells that switch independently. This parameter change in the switching pattern decorrelates the supply current from the digital input data, reducing harmonic distortions while accepting an increase in component quantity.
3Manufacturing precision
If supply current is decorrelated from digital data using dummy switching, then linearity improves, but power consumption increases due to additional switching activity
Solution Approach 1:
Instead of switching all DAC cells for every input change, only a subset of dummy DAC cells is switched based on dummy data. This partial action approach achieves the necessary decorrelation for improved linearity while limiting the excessive power consumption that would result from switching all cells continuously.
Data Source
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AI summary
A digital-to-analog converter comprises a plurality of first digital-to-analog converter cells configured to generate a first analog signal based on first digital data, wherein the first digital-to-analog converter cells of the plurality of first digital-to-analog converter cells are coupled to a first output node for coupling to a first load. Further, the digital-to-analog converter comprises a plurality of second digital-to-analog converter cells configured to generate one or more second analog signals based on second digital data, wherein the second digital-to-analog converter cells of the plurality of second digital-to-analog converter cells are coupled to one or more second output nodes, and wherein the plurality of first digital-to-analog converter cells and the plurality of second digital-to-analog converter cells are coupled to a power supply node for coupling to a mutual power supply.