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The ever-increasing switching speed of semiconductor devices requires a precise measurement of steep current transients. The M-shunt concept offers high signal fidelity, good cooling, and simple manufacturing. Depending on the resistive material used, temperature as well as skin and proximity effects impede static and dynamic measurements to a different degree. A step forward has been derived from the ideal coaxial shunt, so far, a purely theoretical concept, which is hardly producible due to its sophisticated structure. By transferring this concept to the M-shunt structure with its improved PCB manufacturing technologies it can now be realised in practice. Nevertheless, the calibration and the correct degree of delay compensation remain challenging and are investigated more closely within this paper. Furthermore, it will be discussed why the conventional method of bandwidth determination doesn't work for the M-shunt structure. In addition to the low inductance introduced into the load circuit, the high bandwidth of the shunts could be demonstrated, as well as the possibility to extend this by design rules. Supplemented by the advantages of the lower load inductance, the M-shunt will become the tool of choice for characterising switching transients at least up to 200 MHz required bandwidth eventually. Although it is obviously difficult to improve the 3 dB bandwidth with suitable design rules, the range of nearly entirely unaffected measurement frequencies (e.g. < 1 dB) can be significantly extended by limited coupling. For even higher frequencies, measurements of the current M-shunt models, as well as for the coaxial shunts used as reference, should be corrected by post processing to get precise measurement results.
Most current measurement techniques suffer from temperature impacts, though to a different degree. This is also true for shunt resistors, which are usually improved significantly by using temperature compensated alloy materials like Manganin(r) or by proper calibration and subsequent temperature compensation. The concept of the copper-based PCB M-shunt has already been reported to yield excellent current measurement results at room temperature. However, due to the high-temperature coefficient of copper (3920 ppm/K), the current measurement with those M-shunts showed considerable measurement errors for high temperatures and due to self-heating. This can be improved by the use of Manganin. However, still the connection of the resistor with the copper of the PCB and their respective thermal behavior needs to be considered as further possible sources of error. This paper presents challenges associated with the improvement of PCB-based shunts by temperature-compensated material, while not compromising the critical issue of bandwidth and manufacturing capability. It explicitly addresses the problems and difficulties as reported for previous development stages. In its new version, the M-shunt, represents a low inductance measurement system that can be optimised for much higher energies than the coax shunt, while not increasing the inductance introduced into the circuit. Alternatively, it can be configured for a significantly increased bandwidth and lower inductance compared to its coaxial reference.