Digitally Trimmed DAC Architecture for DNL Error Correction
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Solution Overview
Problem
Digital-to-analog converters (DACs) face challenges in achieving accurate output voltages due to differential nonlinearity (DNL) errors, which can exceed one least significant bit (LSB) voltage, affecting their performance and requiring complex correction methods.
Innovation Solution
A digital-to-analog converter (DAC) with a controller that generates an output code based on input code and DNL errors, using a segmented R2R DAC architecture with thermometric and binary arms, and trim arms to adjust output voltage, ensuring the output voltage differs from the ideal by less than one LSB voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional DAC architecture is used, then device simplicity is maintained, but DNL errors exceed one LSB voltage affecting performance
Solution Approach 1:
The DAC is divided into multiple segments including a main DAC portion and a trim DAC portion. The trim DAC consists of multiple trim arms that can be independently controlled to correct DNL errors in specific segments of the output code range, allowing localized correction without complicating the entire DAC structure.
Solution Approach 2:
A controller acts as an intermediary between the digital input code and the DAC switches. The controller generates trim codes that activate specific trim arms to compensate for DNL errors, effectively mediating the correction process without requiring complex analog circuitry in the DAC itself.
2Manufacturing precision
If auxiliary trim DACs are added to correct DNL errors, then manufacturing precision is improved, but device complexity and circuit overhead increase
Solution Approach 1:
The trim DAC functionality is merged with the main DAC structure by sharing the same reference voltage terminal, output terminal, and control logic. The trim arms are integrated into the existing DAC architecture, eliminating the need for separate auxiliary trim DAC circuits and reducing overall device complexity.
Solution Approach 2:
The trim arms serve multiple functions: they correct DNL errors, provide fine-adjustment capability for output voltage, and can operate in conjunction with the main DAC portions. This multi-functionality reduces the need for dedicated correction circuits, thereby reducing circuit overhead.
3Manufacturing precision
If DNL errors are corrected using complex correction methods, then output voltage accuracy is improved, but design complexity increases
Solution Approach 1:
The invention changes the control parameters by introducing trim codes that selectively activate trim arms based on the input code range. This parameter-based control approach simplifies the design compared to complex analog correction circuits, as it uses digital control logic to achieve precision correction.
Data Source
AI summary
In described examples, a digital-to-analog converter (DAC) includes an output, a ground, a reference voltage terminal, an input code terminal, multiple switches, multiple resistors, and a controller. The switches couple to the reference voltage terminal when activated and to the ground when deactivated. The resistors are variously coupled between corresponding ones of the switches and the output, so that activating the switches causes the DAC to output an output voltage. The controller is coupled to the input code terminal and coupled to control the switches. The controller generates an output code based on an input code in response to at least one differential nonlinearity error greater than one least significant bit voltage. The input code corresponds to a first ideal output voltage, the output code corresponds to a second, different ideal output voltage. The controller generates an output voltage by controlling the switches using the output code.