Thermometric-R2R DAC Architecture for Low-Current Monotonic Resolution
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Solution Overview
Problem
Existing digital to analog converters (DACs), particularly R2R DACs, face challenges in achieving fine resolution at low current operation while maintaining monotonicity, which is crucial for battery-operated medical devices that require low power consumption and longevity.
Innovation Solution
The implementation of a combinational thermometric-R2R DAC circuit that includes a thermometric DAC for coarse output steps and an R2R circuit for fine output steps, along with a resistor in series, allowing for a smaller IC area and low current operation with fine resolution of two nanoamps per bit, ensuring monotonicity throughout the output range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a R2R DAC is used to achieve fine resolution, then the output resolution is improved, but the current consumption increases and monotonicity cannot be maintained at low current operation
Solution Approach 1:
The DAC is divided into two independent circuits: a thermometric DAC circuit for coarse output steps and an R2R DAC circuit for fine output steps. This segmentation allows each circuit to operate in its optimal regime, with the thermometric circuit providing robust low-current operation and the R2R circuit providing fine resolution, thereby resolving the contradiction between fine resolution and low current consumption.
Solution Approach 2:
The patent introduces a new dimension to the DAC architecture by combining two different DAC topologies (thermometric and R2R) that operate in parallel with different functionality. The thermometric circuit handles the coarse quantization while the R2R circuit handles the fine quantization, effectively adding a dimensional separation of functions that allows both low power consumption and fine resolution to coexist.
2Use of energy by moving object
If a thermometric DAC is used for low current operation, then power consumption is reduced, but output resolution becomes coarse
Solution Approach 1:
The overall DAC resolution is segmented into two parts: coarse resolution from the thermometric DAC and fine resolution from the R2R DAC. The thermometric portion handles the majority of the quantization levels with low power consumption, while the R2R portion adds the fine resolution steps, thereby achieving both low power consumption and high overall resolution.
Solution Approach 2:
The patent merges two different DAC circuits (thermometric and R2R) into a single combinational architecture where their outputs are combined. The thermometric DAC provides the coarse output and the R2R DAC provides the fine output adjustments, and their combination achieves both low power consumption characteristics of thermometric DACs and fine resolution characteristics of R2R DACs.
3Measurement precision
If an R2R DAC is used to achieve fine resolution, then the output resolution is improved, but the IC area increases
Solution Approach 1:
The DAC functionality is segmented between two circuits with different area characteristics. The thermometric DAC requires smaller IC area for a given resolution, while the R2R DAC is designed to provide only the fine resolution portion. This segmentation allows the overall system to achieve fine resolution without requiring a full-resolution R2R DAC, thereby reducing the total IC area.
Data Source
AI summary
The disclosure describes an implementation of a combinational thermometric-R2R that includes a thermometric DAC circuit to output the coarse output steps, an R2R circuit to control the fine output steps, and a resistor in series with the thermometric and R2R circuits. The techniques of this disclosure implement a fine resolution DAC, on the order of two nanoamps per bit, that operates at low current, yet maintains monotonicity throughout the DAC output range.