Segmented DAC Current Switching for Monotonic Output

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Solution Overview

Problem

Existing digital-to-analog converters (DACs) face challenges in achieving monotonicity while minimizing the number of switches, which affects the size and error rates of the converters.

Innovation Solution

The method involves a digital-to-analog converter (DAC) circuit with a switching circuit that decouples a current source from a least-significant bit (LSB) transconductance stage and couples it to a most-significant bit (MSB) transconductance stage when there is a change in the MSBs and LSBs by specific thresholds, ensuring consistent current source error and monotonic output.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a segmented DAC is used to convert MSBs and LSBs separately, then the DAC can be implemented with fewer components, but the monotonicity of the output is degraded

Engineering Contradiction:

Improvenumber of switchesVSAvoidmonotonicity

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies dynamics by making the current source coupling configurable rather than fixed. The switching circuit dynamically reconfigures which transconductance stage (MSB or LSB) receives current from each current source based on the digital input code. This dynamic reconfiguration ensures that the same current sources are used consistently across different output ranges, maintaining monotonicity while allowing the DAC to operate with a segmented structure that reduces the total number of switches required.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses segmentation by dividing the DAC into separate MSB and LSB transconductance stages. However, unlike conventional segmented DACs that use different current sources for each segment, this patent segments the functionality while sharing the same current sources between segments. The switching circuit directs current from shared current sources to either the MSB or LSB stage depending on the input code, achieving area reduction through segmentation while maintaining monotonicity through shared current sources.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If different current sources are used for MSB and LSB transconductance stages, then the DAC can operate independently for each segment, but the error rates increase due to inconsistent current source errors

Engineering Contradiction:

Improveindependent segment operationVSAvoiderror rate

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies universality by making the same current sources serve multiple functions - they can supply current to either the MSB transconductance stage or the LSB transconductance stage depending on the switching circuit configuration. This multi-functionality ensures that a single set of current sources is used across different output ranges, guaranteeing that the same current source errors apply consistently whether the output is in the MSB range or LSB range, thereby eliminating the error inconsistency problem while maintaining independent segment operation capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP4513764A1Digital-to-analog converter

Publication Date: 2025.02.26 ANALOG DEVICES INT UNLTD CO

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AI summary

There is provided a method for controlling a digital-to-analog converter, DAC. The DAC receives a digital input comprising a plurality of bits including a first segment comprising X most significant bits, MSBs, and a second segment comprising Y least significant bits, LSBs. The DAC modifies the connection of a plurality of current sources, changing the current source coupling between LSB and MSB transconductance stages. By doing this, the monotonicity of the system can be improved in a compact DAC.