Resistor-String DAC Layout With Fewer Higher-Order Switches
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Solution Overview
Problem
Resistor string type D/A converters require a large number of switches, leading to increased chip size due to the need for two switches between each pair of resistors, which complicates the design and increases the physical size of the converter.
Innovation Solution
A resistor string type D/A converter design that eliminates the need for multiple switches between each pair of higher-order analog voltages by using a higher-order resistor string with controlled switches and decoders to generate control signals for neighboring switches, reducing the overall number of switches required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two switches are provided between each pair of resistors in the higher-order resistor string, then the D/A converter can achieve high resolution and accurate voltage selection, but the chip size becomes larger due to the increased number of switches
Solution Approach 1:
The patent extracts and eliminates the redundant switch connected to the common potential point (ground or reference voltage). By removing this unnecessary switch while keeping the essential switch connected to the signal line, the design maintains the ability to select voltage levels while reducing the total switch count by approximately half, thus reducing chip size without compromising conversion accuracy.
Solution Approach 2:
The patent discards the redundant switch that connects to the common potential point, recognizing that its function is already provided by the common potential itself. The essential switching function is recovered and maintained through the single remaining switch that controls connection to the signal line, thereby eliminating unnecessary components while preserving the required functionality.
2Measurement precision
If a higher-order and lower-order division scheme is employed, then the D/A converter can achieve high resolution with reduced size, but the device complexity increases due to the need for multiple decoders and switch control mechanisms
Solution Approach 1:
The patent segments the D/A converter into higher-order and lower-order sections, each with their own resistor strings and decoders. This segmentation allows independent optimization of each section, enabling high overall resolution while managing complexity through modular design. The higher-order section handles coarse voltage selection while the lower-order section handles fine adjustments.
Solution Approach 2:
The patent employs a universal switch structure where the same basic switch design is used throughout both higher-order and lower-order sections. This multi-functional approach allows the same switch template to be replicated and reused, simplifying the overall control architecture despite the segmented design, and reducing the variety of unique control circuits needed.
Data Source
AI summary
A resistor string type D/A converter in accordance with an exemplary aspect of the present invention includes a resistor string, switches, a higher-order decoder, a lower-order decoder, and a conversion unit. The resistor string generates a plurality of analog voltages by dividing a voltage between a first reference voltage and a second reference voltage. Each of the switches is provided for a respective one of a plurality of voltage drawing points. The higher-order decoder generates a higher-order control signal according to the value of higher bits of an input digital signal. The lower-order decoder generates a lower-order control signal corresponding to the value of lower bits of the input digital signal. The conversion unit outputs a voltage between a pair of the analog voltage values obtained through a pair of switches based on the lower-order control signal.