Segmented DAC Circuit for Linear Gamma Voltage Output
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Solution Overview
Problem
Conventional resistor string digital-to-analog converters (DACs) face area inefficiency and distortion issues due to the limited voltage input range of operational amplifiers, leading to non-linear gamma curves, especially when processing large voltage differences.
Innovation Solution
A digital-to-analog converter design that includes an R-string section, a first DAC section, a second DAC section, a multiplexer, and an operational amplifier, where the R-string section provides two groups of voltage levels, and the multiplexer averages intermediate voltages from these levels to linearly process high and low end voltage levels, reducing the number of select lines and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional R-string DAC uses 2N select lines to convert N bits of data, then the converter can accurately process all voltage levels, but the chip area becomes excessively large and area inefficient
Solution Approach 1:
The patent divides the N-bit input word into two parts: remaining bits (N-1 bits) and LSB (1 bit). The R-string section is segmented to provide two groups of voltage levels, with the first group handling voltages near the lower rail and the second group handling voltages near the upper rail. This segmentation allows the use of fewer select lines (2N-1 instead of 2N) while maintaining accurate voltage level selection through the coordinated operation of the first DAC section, second DAC section, and multiplexer.
2Adaptability or versatility
If an operational amplifier processes very large voltage differences to expand the input range, then the voltage input range increases, but the gamma curve becomes distorted and non-linear
Solution Approach 1:
The patent applies local quality by creating different processing paths for different voltage ranges. The first DAC section handles voltage levels near the lower rail (first group), while the second DAC section handles voltage levels near the upper rail (second group). The multiplexer selectively connects to either the first or second DAC section based on the input voltage range, ensuring that each group is processed within the linear operating range of the operational amplifier, thus maintaining gamma curve linearity across the entire input range.
Solution Approach 2:
The multiplexer acts as an intermediary that selectively connects the operational amplifier to either the first DAC section or the second DAC section based on the input voltage level. This intermediary component enables the system to switch between different voltage processing paths, ensuring that the operational amplifier always receives input within its linear operating range, thereby preventing gamma curve distortion while maintaining a wide effective input range.
3Area of stationary object
If a dual output DAC reduces select lines from 2N to 2N-1, then chip area is saved, but the operational amplifier still experiences distortion when processing extreme voltage levels
Solution Approach 1:
The patent further segments the voltage processing by dividing the voltage range into two distinct groups: the first group near the lower rail handled by the first DAC section, and the second group near the upper rail handled by the second DAC section. This segmentation, combined with the multiplexer, allows the system to maintain the reduced select line count (2N-1) while ensuring that extreme voltage levels are processed through dedicated paths that avoid operational amplifier distortion, thus preserving gamma curve linearity.
Solution Approach 2:
The patent implements local quality by providing specialized processing paths for different voltage regions. The first DAC section is optimized for handling voltage levels near the lower rail, while the second DAC section is optimized for voltage levels near the upper rail. This localized optimization ensures that each voltage group is processed within the linear range of the operational amplifier, eliminating the distortion problems that would otherwise occur when processing extreme voltage levels with a single unified path.
Data Source
AI summary
A digital-to-analog converter is provided. The DAC includes a R-string section, a first DAC section, a second DAC section, a multiplexer, and an operational amplifier. The R-string section provides a first group of voltage levels and a second group of voltage levels. The first DAC section provides the output voltage according to the input word when the input word corresponds to a voltage level within a range of the first group of voltages levels. The second DAC section provides a second and a third voltage levels according to the remaining bits. The multiplexer is coupled to the second DAC section to provide an intermediate voltage from the first and the second voltage levels according to the LSB bit. The operational amplifier averages the intermediate voltage and one of the first and the second voltage levels to generate the output voltage.