High dynamic range current measurements on IoT devices

Current measurement with nine-figure dynamic range

A long battery lifetime is crucial for modern IoT and mobile devices. In order to keep energy consumption as low as possible, these devices typically work with special sleep modes that consume very little power and are only interrupted by very short activity phases of normal or high power consumption. For a device to succeed, its power consumption has to be optimized in the early development phase. It needs to be measured accurately, which requires sophisticated probing solutions. The probe must be able to simultaneously measure very small currents in the μA or even nA range as well as currents up to several amperes. Handling such a high dynamic range of 10⁶ or even up to 10⁹ is a challenge for every measurement device and may even be impossible for digital multimeters, current probes or source meter

Multi-channel power probe

The R&S®RT-ZVC02/-ZVC04 multi-channel probes are ideal for battery lifetime measurements on low power consumption devices. They simultaneously measure current with high dynamic range and high resolution in all mobile device activity phases. To operate the multi-channel probe, an R&S®RTE1000, R&S®RTO2000 or R&S®RTP oscilloscope is required. With up to four current and four voltage input channels, each with 18 bit ADC resolution, the R&S®RT-ZVC02/-ZVC04 multi-channel power probes provide the dynamic range needed to analyze current consumption. Three built-in shunts and an external shunt mode in combination with switchable gain factors help optimize the input current range.

The external shunt mode is beneficial for simultaneous measurement of different current levels. It supports very high dynamic range as well as highest vertical resolution. In shunt mode, two current measurement channels of the R&S®RT-ZVC02/-ZVC04 multi-channel power probe are connected to the same shunt resistor.

By operating the two channels at different sensitivities, it is possible to detect the general current characteristics over all activity phases (zoomed out) as well as small details of an individual phase with highest accuracy (zoomed in).

Zoomed in and zoomed out in one acquisition

The results in the screenshot were achieved by performing a high-side current measurement on a Bluetooth® Low Energy device with an 18 Ω external shunt. The upper trace shows the current during the full advertising event (zoomed out), the measured maximum current (Max) and the consumed charge (Area). It was recorded using the low sensitivity setting (450 mV) of the external shunt mode of the R&S®RT-ZVC04. The lower trace was acquired simultaneously using the same shunt resistor and the high sensitivity setting (45 mV) of the R&S®RT-ZVC04. This zoomed in view helps users observe the smallest details in the current trace. Although the current peaks extend the measurement range of the device in this setting, the small sleep current can be resolved and determined to be about 1.2 μA in a gated measurement (Mean).

Summary

The R&S®RT-ZVC02/-ZVC04 multi-channel probes detect smallest currents with high dynamic range. In external shunt mode, the same measurement can be performed with different sensitivities, making it possible to observe both the general current trend as well as detailed behavior. The probes come with a set of high-quality pin connector cables and solder-in leads for connecting the probes in typical embedded electronics measurement scenarios. Available options include 4 mm connector cables with different lengths as well as BNC type connector cables for connecting standard oscilloscope voltage and current probes to extend the voltage and current measurement range.

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