Segmented DAC Switching for Monotonic Output Transitions

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Solution Overview

Problem

Segmented digital-to-analog converters (DACs) require a large number of switches, which increases area and introduces errors, limiting their practical use and monotonicity.

Innovation Solution

A switching circuit is used to modify the coupling of current sources between least significant bit (LSB) and most significant bit (MSB) transconductance stages, ensuring consistent current source error during transitions to maintain monotonicity with a reduced number of switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a segmented DAC is used to convert MSBs and LSBs separately, then the DAC can be implemented with ladder or string architectures, but the number of switches increases significantly, increasing area and introducing errors

Engineering Contradiction:

ImproveDAC implementation flexibilityVSAvoidnumber of switches

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent combines the MSB and LSB transconductance stages into a unified architecture where current sources are shared between both stages. This merging reduces the total number of switches required compared to completely separate segmented implementations, while maintaining the functional benefits of segmentation for MSB and LSB conversion.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The current sources are designed to serve dual purposes by being coupled to both the LSB transconductance stage and the MSB transconductance stage through a switching circuit. This multi-functionality allows the same current sources to support both segmentation paths, reducing the overall component count and area requirements.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Area of stationary object

If the number of switches is reduced to decrease area, then the DAC becomes more compact, but monotonicity and linearity deteriorate due to increased quantization effects in segmented architectures

Engineering Contradiction:

ImproveDAC areaVSAvoidmonotonicity and linearity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The switching circuit acts as an intermediary between the current sources and the transconductance stages. It dynamically couples current sources to either the LSB or MSB stage based on the input code, ensuring smooth transitions and maintaining monotonicity. This intermediary mechanism allows reduced switch count while preserving precision by coordinating the operation of shared current sources.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If current sources are shared between LSB and MSB stages, then the number of current sources is reduced, but errors from current source mismatches increase

Engineering Contradiction:

Improvenumber of current sourcesVSAvoiderror from current source mismatches

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent employs dynamic coupling of current sources to transconductance stages through a switching circuit that responds to input code changes. This dynamic allocation ensures that at any given time, the appropriate current sources are connected to the appropriate stages, minimizing the impact of mismatches. The system adapts its configuration based on operating conditions, reducing error propagation.

Inventive Principle:

Principle #15Dynamics

4Area of stationary object

If segmentation is applied to reduce the number of switches, then area is reduced, but transition accuracy and monotonicity are compromised

Engineering Contradiction:

ImproveDAC areaVSAvoidtransition accuracy

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The switching circuit monitors the input code and dynamically adjusts the coupling between current sources and transconductance stages. This feedback mechanism ensures that transitions between MSB and LSB stages occur accurately, maintaining monotonicity and transition precision. The system detects when switching is needed and executes it at the appropriate moment, preventing errors that would otherwise occur with static segmentation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS20250279784A1Digital-to-analog converter

Publication Date: 2025.09.04 ANALOG DEVICES INT UNLTD CO

AI summary

There is provided a digital-to-analog converter, DAC. The DAC circuit comprises an input for receiving a digital input comprising a plurality of bits; an LSB transconductance stage; an MSB transconductance stage; a plurality of current sources, the plurality of current sources comprising a first current source and a second current source; and a switching circuit, the switching circuit configurable to modify a coupling between the plurality of current sources and the LSB transconductance stage and the MSB transconductance stage, wherein the switching circuit is configured to: couple the first current source to one of the LSB transconductance stage and the MSB transconductance stage, and couple the second current source to the other of the LSB transconductance stage and the MSB transconductance stage. A third, binary, transconductance stage may also be present.