Resistor-Ladder DAC Switching for Low Nonlinearity Accuracy
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Solution Overview
Problem
Existing digital-to-analog converter (DAC) designs face limitations in accuracy due to switches or methods used to project the most significant bits (MSB) voltage range on the least significant bits (LSB) ladder, leading to errors in generating the desired analog value.
Innovation Solution
The use of p-channel depletion devices as both switching and resistive elements eliminates the need for large switches and operational amplifiers, with a MSB resistor ladder coupled to a LSB resistor ladder through switching units formed by p-channel depletion transistors, allowing for accurate voltage projection and compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional switches or methods are used to project MSB voltage range on LSB ladder, then the DAC can be implemented with standard components, but accuracy deteriorates with errors up to 12 or more LSBs
Solution Approach 1:
The patent combines the MSB and LSB resistor ladders into a unified resistor network where MSB resistors are connected in parallel with corresponding LSB resistors. This merging eliminates the need for separate switching mechanisms to project MSB voltage onto the LSB ladder, thereby improving accuracy to within less than +/- 1 LSB while reducing device complexity.
Solution Approach 2:
Each resistor in the unified ladder serves multiple functions: it contributes to both the MSB and LSB voltage division simultaneously. The switching units selectively connect these multi-functional resistors to different nodes, allowing a single resistor structure to perform what previously required separate MSB and LSB ladder projections.
2Device complexity
If separate MSB and LSB resistor ladders are used, then the DAC structure can be simplified, but accuracy deteriorates due to projection errors
Solution Approach 1:
The patent merges separate MSB and LSB resistor ladders into a single unified resistor network where resistors are connected in parallel between common nodes. This unified structure maintains simplicity while eliminating projection errors by allowing direct voltage division across the entire resistor range without intermediate switching projections.
Solution Approach 2:
The switching units act as intermediaries that selectively connect specific parallel resistor pairs to form the effective resistance for each digital code. This intermediary switching mechanism enables accurate analog output by dynamically configuring the unified resistor network without requiring separate MSB and LSB projection paths.
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 significantly reduces integral nonlinearity errors, achieving accuracy within less than +/- 1 LSB, compared to conventional DACs which can have errors of up to 12 or more LSBs, thereby enhancing the precision of the digital-to-analog conversion.
Implementation Method 1
each switching unit comprises a first switch for connecting a first terminal of an associated MSB resistor with a first terminal of the LSB resistor ladder and a second switch for connecting a second terminal of the associated MSB resistor with a second terminal of the LSB resistor ladder
Implementation Method 2
each switch is configured form a resistor of similar value of the resistors of the LSB resistor ladder when switched on
Implementation Method 3
providing an MSB resistor ladder comprising a plurality of series connected resistors between a first and second reference potential; providing an LSB resistor ladder comprising a plurality of series connected resistors
Data Source
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AI summary
A digital-to analog-converter (DAC) has a MSB resistor ladder with a plurality of series connected resistors, wherein the MSB resistor ladder is coupled between a first and second reference potential, a LSB resistor ladder with a plurality of series connected resistors, and a plurality of switching units for connecting one of the series connected resistors of the MSB resistor ladder with the LSB resistor ladder, wherein each switching unit has a first switch for connecting a first terminal of an associated MSB resistor with a first terminal of the LSB resistor ladder and a second switch for connecting a second terminal of the associated MSB resistor with a second terminal of the LSB resistor ladder and wherein each switch is configured form a resistor of similar value of the resistors of the LSB resistor ladder when switched on.