Thermometer DAC Cell Shifting for Lower Harmonic Distortion
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Solution Overview
Problem
Thermometer encoded Digital-to-Analog Converter (DAC) architectures suffer from systematic errors leading to harmonic distortions due to non-identical DAC cells, which are not effectively addressed by existing technologies.
Innovation Solution
The proposed solution involves a DAC design with a shift code generation circuit that generates a pseudorandom shift code based on the difference between input digital control codes, reducing the correlation between the input code and activated DAC cells, thereby minimizing harmonic distortions and noise. This is achieved through a circuit that includes a code difference determination circuit, a pseudorandom number generator, and a combiner circuit to modify and accumulate the shift code, ensuring a pseudorandom selection of DAC cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed cell selection is used for each digital code, then the DAC structure is simple, but systematic errors and harmonic distortions occur due to non-identical cells
Solution Approach 1:
The patent applies dynamics by making the cell selection variable rather than fixed. A shift code is generated that dynamically changes which DAC cells are activated for each digital code, preventing systematic errors while maintaining simplicity. The shift code modifies the cell activation pattern dynamically without requiring complex additional circuitry.
Solution Approach 2:
The patent changes the selection parameter of DAC cells from fixed to variable by introducing a shift code. This parameter change allows different cells to be selected for the same digital code at different times, reducing the impact of non-identical cell characteristics and minimizing harmonic distortions.
2Manufacturing precision
If pseudorandom shift code is generated to reduce correlation, then harmonic distortions are minimized, but the circuit complexity increases
Solution Approach 1:
The patent introduces a shift code generation circuit as an intermediary component that produces pseudorandom shift codes. This intermediary element modifies the cell selection process without requiring complete redesign of the DAC structure, achieving distortion reduction with minimal added complexity.
Solution Approach 2:
The patent uses a simplified approach where the shift code generation circuit creates a modified version of the original digital code by applying a pseudorandom shift pattern. This copying mechanism allows the same DAC structure to be used with improved performance by simply modifying the activation pattern.
3Measurement precision
If more DAC cells are activated to improve resolution, then the output precision increases, but the power consumption increases
Solution Approach 1:
The patent applies partial action by activating only the necessary number of DAC cells required to achieve the desired resolution, rather than activating all cells. The pseudorandom shift code ensures that the minimum required cells are activated while distributing the activation pattern to reduce correlation effects, thereby maintaining precision with reduced power consumption.
Data Source
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AI summary
A digital-to-analog converter is provided. The digital-to-analog converter comprises an input configured to receiving a first digital control code for controlling a plurality of digital-to-analog converter cells. Further, the digital-to-analog converter comprises a code converter circuit configured to converter the first digital control code to a second digital control code. Further, the digital-to-analog converter comprises a shift code generation circuit configured to generate a shift code based on a code difference between the first digital control code and a third digital control code. The digital-to-analog converter additionally comprises a bit-shifter circuit configured to bit-shift the second digital control code based on the shift code in order to obtain a modified second digital control code. The digital-to-analog converter comprises a cell activation circuit configured to selectively activate one or more of the plurality of digital-to-analog converter cells based on the modified second digital control code. Each activated digital-to-analog converter cell is configured to output a respective cell output signal. Further, the digital-to-analog converter comprises an output configured to output an analog output signal based on the cell output signals