Segmented Resistor-String D/A Converter to Prevent Bit Inversion
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Solution Overview
Problem
Multi-bit D/A converter circuits face issues with bit inversion and large layout area, particularly in six-bit or more systems, where existing resistor string and R-2R ladder resistor designs either suffer from bit inversion or require excessive space.
Innovation Solution
A D/A converter circuit utilizing a three-stage resistor string structure with switching circuits and buffers to select and generate analog voltages, reducing the number of resistors and switches while preventing bit inversion, and incorporating adjusting resistors to mitigate abrupt changes in analog output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an R-2R ladder resistor D/A converter circuit is used, then the layout area is reduced, but bit inversion occurs in six-bit or more systems
Solution Approach 1:
The digital input signal is divided into upper bits and lower bits. The upper bits control a first switching circuit that selects from voltages generated by a first resistor string, while the lower bits control a second switching circuit that selects from voltages generated by a second resistor string. This segmentation allows the circuit to achieve accurate D/A conversion without bit inversion while maintaining a compact layout area.
2Reliability
If a resistor string D/A converter circuit is used, then bit inversion is prevented, but the layout area becomes very large (five times larger than R-2R type)
Solution Approach 1:
The resistor string is divided into two separate resistor strings (first and second). The first resistor string handles the upper bits and the second resistor string handles the lower bits. This segmentation reduces the number of resistors and switches needed compared to a full resistor string implementation, thereby reducing the layout area while still preventing bit inversion.
Solution Approach 2:
The circuit transitions from a single-dimensional resistor string to a two-dimensional structure with parallel first and second resistor strings. Each resistor string handles a portion of the bit resolution, allowing the circuit to achieve the same functionality with fewer total components and reduced layout area.
3Area of stationary object
If the number of resistors and switches is reduced, then the layout area is reduced, but conversion accuracy may be compromised
Solution Approach 1:
The digital input is segmented into upper and lower bits, each handled by separate switching circuits and resistor strings. This segmentation allows each subset of bits to be processed with fewer components while maintaining overall conversion accuracy through the combined output of both paths.
Solution Approach 2:
Buffers are introduced as intermediary elements between the first and second resistor strings and the final output. These buffers isolate the voltage selection circuits from the final D/A conversion stage, ensuring that the reduced number of resistors and switches does not compromise conversion accuracy.
Data Source
AI summary
A multi-bit D/A converter circuit that prevents a bit inversion and requires a reduced layout area is offered. A first switching circuit is provided in order to select a pair of analog voltages generated across one of resistors in a first resistor string. The selected pair of analog voltages is provided as reference voltages to a second resistor string. A second switching circuit is provided in order to select a pair of analog voltages generated across one of the resistors in the second resistor string. The selected pair of analog voltages is provided as reference voltages to a third resistor string. A third switching circuit is provided in order to select one of analog voltages generated in the third resistor string.