Isolated Current Shunt Probe for High Common-Mode Rejection

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Solution Overview

Problem

Existing current measurement techniques face challenges in accurately measuring dynamic currents due to the need for high common-mode rejection ratio (CMRR) and the compensation of inductive effects in current shunts, which are not practical for general circuit probing during the design phase.

Innovation Solution

An isolated current-shunt measurement probe with a galvanic isolation barrier and a low-noise amplifier with low input impedance is used to measure the voltage drop across a current shunt, while minimizing the inductive effect through careful design and placement of measurement leads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a low-value current shunt is used to measure current, then the impact on the device under test is minimized, but the voltage drop across the shunt becomes very small and difficult to measure in the presence of high common-mode voltage

Engineering Contradiction:

Improvepower loss in shuntVSAvoidvoltage measurement accuracy

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

An isolated measurement probe with galvanic isolation acts as an intermediary between the high common-mode voltage environment and the measurement instrument. The probe includes a high common-mode rejection amplifier that can measure the small shunt voltage drop while rejecting the large common-mode voltage, enabling accurate measurement without affecting the DUT.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct electrical connection with galvanic isolation technology, substituting the mechanical/electrical coupling with an isolated measurement system that uses capacitive or magnetic coupling to transfer the measurement signal while blocking the common-mode voltage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If a permanently-attached measurement probe is used, then the inductive effect can be compensated with analog hardware or digital signal processing, but the complexity increases and compensation may not be practical for general probing during design phase

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidcompensation circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The measurement probe is designed with exchangeable tips that can be configured for different measurement scenarios. The system dynamically adapts to different measurement needs by allowing the user to select appropriate probe tips rather than requiring complex fixed compensation circuits for all scenarios.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the inductance parameter of the measurement loop by using probe tips with optimized geometries and lead placements. By varying the physical parameters of the probe tip (such as loop area and lead routing), the inductive effects are minimized directly in the hardware rather than requiring software compensation.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If the measurement leads are placed to minimize inductive effect, then the voltage measurement accuracy improves, but the placement requirements become more stringent and difficult to achieve

Engineering Contradiction:

Improvevoltage drop measurement accuracyVSAvoidprobe assembly difficulty

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The optimal lead placement and probe tip geometry are predetermined and built into the probe design during manufacturing. The low-inductance configuration is pre-engineered into the probe tip structure, eliminating the need for complex manual placement procedures during assembly or use.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution achieves low-noise measurements of dynamic currents with high common-mode rejection, effectively addressing the challenges of measuring small voltage drops in the presence of high common-mode voltages and minimizing the impact of inductive effects.

Implementation Method 1

an input side including a low-noise, low-impedance input configured to receive a voltage signal across a current shunt

Methodology Applied

Scientific EffectLow-noise amplification:

Implementation Method 2

an isolated current-shunt measurement probe with a galvanic isolation barrier

Methodology Applied

Scientific EffectGalvanic isolation:

Data Source

PatentUS12235291B2Current shunt probe

Publication Date: 2025.02.25 TEKTRONIX INC

AI summary

An isolated differential current shunt measurement probe for a test and measurement system having an isolation barrier between an input side and output side of the probe. The input side is configured to receive a voltage signal across a current shunt connected to a device under test and transmit the voltage signal across the isolation barrier. The output side is configured to receive the voltage signal across the isolation barrier and output the voltage signal to a test and measurement instrument.