Dual-Stage Source Measure Unit Digital Loop Architecture

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Solution Overview

Problem

Existing source measure units (SMUs) utilize a single digital control loop, which limits their ability to independently control voltage across a device under test (DUT) and current through the DUT, leading to common mode measurement errors.

Innovation Solution

A dual-stage SMU is designed with two digital control loops, one for voltage and one for current, allowing independent control and measurement without affecting each other, thereby eliminating common mode measurement errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single digital control loop is used in SMU, then the device complexity is reduced, but the measurement precision deteriorates due to common mode measurement errors

Engineering Contradiction:

Improvecontrol loop structureVSAvoidvoltage and current measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent divides the single control loop into two independent digital control loops: a voltage control loop and a current control loop. Each loop independently controls its respective parameter (voltage or current) without interfering with the other, thereby eliminating common mode measurement errors and improving measurement precision while maintaining reasonable device complexity through modular architecture

Inventive Principle:

Principle #1Segmentation

2Ease of operation

If a single digital control loop is used in SMU, then the ease of operation is maintained, but the reliability deteriorates due to inability to independently control voltage and current

Engineering Contradiction:

Improvecontrol interface simplicityVSAvoidindependent control capability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent implements separate voltage and current control loops that can be independently activated based on measurement mode (voltage mode or current mode). This segmentation allows the system to maintain ease of operation through a unified interface while achieving reliable independent control of voltage and current parameters when needed

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control system dynamically switches between voltage mode and current mode operation, and can transition between using one control loop or both control loops simultaneously. This dynamic adaptability ensures the system maintains simplicity when basic operation is needed while providing full independent control capability when required for precise measurements

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12265115B2Digital loop dual-stage source measure unit

Publication Date: 2025.04.01 KEITHLEY INSTRUMENTS LLC

AI summary

A dual-stage source measure unit (SMU) has a user interface to allow a user to input one or more target values, at least two terminals to couple to a device under test (DUT), a current loop having a current digital control loop (DCL), a current digital-to-analog converter (DAC), a sense resistor, a current analog-to digital converter (ADC), and a common ADC, the current DCL to receive inputs from the current ADC, from the common ADC, and a target value for the output current, and to control a first output stage to produce the output current, and a voltage loop having a voltage DCL, a voltage DAC, a voltage ADC, and the common ADC, the voltage DCL to receive inputs from the voltage ADC, from the common ADC, and a target value for the output voltage, and to control a second output stage to produce the output voltage.