New-Tech Europe Magazine | July 2016 | Digital edition

Figure 1. The load current profile for a typical wireless device includes long periods of low current consumption with short bursts of high current consumption when the device is stimulating or transmitting data

the voltage across the sense resistor with a digital multimeter (DMM). However, it would be very challenging to choose the appropriate value for the sense resistor. A small resistor value adds only a small additional error to the load current measurement, but if

the value is too small, the DMM might lack sufficient sensitivity to measure the low sleep mode current, or even the standby mode current, accurately. Although an oscilloscope is well suited to the task of capturing the magnitude of short, active-mode load current

off some measurement accuracy and resolution to get speed. Figure 1 illustrates a typical load current profile for a wireless IoT device. In sleep mode, the current is very low, but when the device is transmitting, the load current rises dramatically for a short period. To measure this current, the test instrumentation must respond to control signals that indicate when the device is transitioning into the active state so that the instrumentation can initiate the high-speed measurement. The instrument should also allow flexibility in selecting a measurement time so that the best measurement can be acquired. Because the requirements for making accurate low current measurements during sleep and standby modes and those for making very fast high current measurements during the active mode are so different, one might assume that multiple instruments would be required tomake thesemeasurements. For example, it would be possible to put a sense resistor in series with the test lead that connects a power supply to the device-under-test and measure

Figure 1. The load current profile for a typical wireless device includes long periods of low current consumption with short bursts of high current consumption when the device is stimulating or transmitting data.

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