Measuring current sounds straightforward. In practice, doing it accurately in fast-switching power electronics is one of the more demanding measurement challenges around — and the M-Shunt was developed specifically to meet it.
The problem with fast switching
Modern power semiconductors based on SiC and GaN switch in nanoseconds. That speed is what makes them efficient — but it also means that current can change by hundreds of amperes within a few nanoseconds. To capture that faithfully, a current sensor needs high bandwidth, low parasitic inductance, and enough physical compactness to fit into a switching circuit without disturbing it.
Conventional shunt resistors work well at lower speeds but run into trouble here. Their parasitic inductance introduces measurement errors precisely when the current is changing fastest. Rogowski coils and Hall-effect sensors have their own bandwidth and integration challenges. None of them combine high bandwidth, low inductance, and small footprint cleanly.
The coaxial principle
The M-Shunt is based on the coaxial shunt resistor concept — a design in which the measurement path runs through the centre of a cylindrical current-carrying conductor. By Ampere’s law, the magnetic field inside such a conductor is shielded from external fields, which means the measurement loop sees only the voltage drop across the resistor and not the electromagnetic interference from the switching circuit around it. The result is high EMI stability alongside high measurement bandwidth.
What makes the M-Shunt distinctive is how this principle is implemented on a PCB. The design, developed at the University of Bremen, integrates the coaxial structure into a compact, surface-mountable form factor — small enough to fit directly into a power module or test setup without adding significant parasitic inductance to the current path.
Fig. 1: Key properties of the M-Shunt.
What it enables
The combination of properties — high bandwidth, low insertion inductance, high current capability, and EMI stability — makes the M-Shunt suitable for measurement tasks that other sensors struggle with: Double Pulse Tests on SiC and GaN devices, current sensing inside power modules, and applications where the sensor must sit directly in the switching loop without compromising its behaviour.
It also opens up measurement paths that were previously impractical, such as placing a sensor in the Kelvin Source path of a multi-chip module to detect current asymmetries between parallel chips — something conventional probes cannot do at the required bandwidth and footprint.
More details on how the M-Shunt is applied in practice can be found in our application notes and published papers.