Resistive DAC Cell Layout for Output Linearity in MOS Drivers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern transmitters face challenges in achieving optimal linearity due to the non-linear output impedance of driver circuits in Digital-to-Analog Converters (DACs), particularly in Metal-Oxide-Semiconductor (MOS) technology, which affects the conversion of digital data to analog signals.
Innovation Solution
Incorporating a resistive element with a resistance of at least 20Ω, such as a thin film or polysilicon resistor, between the driver circuit and the capacitive element in DAC cells to desensitize the DAC to resistance variations, thereby linearizing the output stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If driver circuits (inverter circuits or logic circuits) are used to drive output signals of DAC cells, then the DAC can convert digital data to analog signals, but the non-linear output impedance of the driver circuit degrades the linearity of the DAC
Solution Approach 1:
A resistive element is introduced as an intermediary component between the driver circuit and the capacitive element in the DAC cell. This resistor linearizes the output impedance by dominating the impedance characteristics, thereby compensating for the non-linearity of the driver circuit and improving overall DAC linearity
Solution Approach 2:
The output impedance characteristics of the DAC cell are modified by adding a resistive element that changes the overall impedance profile. This parameter change linearizes the output stage, making the impedance more predictable and less dependent on the non-linear driver circuit behavior
2Ease of manufacture
If MOS technology is used to implement driver circuits, then the DAC can be manufactured with standard semiconductor processes, but the unequal on-resistance of NMOS and PMOS components creates non-linear output impedance
Solution Approach 1:
The resistive element serves as a mediator that decouples the linearity requirements from the driver circuit implementation. By placing the resistor between the driver and capacitive element, it masks the non-linear impedance variations caused by unequal NMOS/PMOS on-resistances, allowing standard MOS fabrication to be used while achieving better linearity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the linearity of the DAC, allowing for improved conversion of digital data to analog signals, leading to better performance in transmitters, especially in communication standards that demand higher accuracy.
Implementation Method 1
Incorporating a resistive element with a resistance of at least 20Ω, such as a thin film or polysilicon resistor, between the driver circuit and the capacitive element in DAC cells to desensitize the DAC to resistance variations, thereby linearizing the output stage
Data Source
AI summary
A digital-to-analog converter is provided. The digital-to-analog converter includes a plurality of digital-to-analog converter cells coupled to an output node of the digital-to-analog converter. At least one of the plurality of digital-to-analog converter cells includes a capacitive element configured to generate an analog cell output signal based on a drive signal. The at least one of the plurality of digital-to-analog converter cells further includes a driver circuit configured to generate the drive signal, and a resistive element exhibiting a resistance of at least 20Ω. The resistive element is coupled between the driver circuit and the capacitive element or between the capacitive element and the output node.