FEATURE TEST & MEASUREMENT DEBUGGING IOT MODULES Intelligent IoT modules communicate between industrial facilities, machines and
Hi-Fi devices, as well as between household appliances and mobile phones. They bring together multiple technologies into the smallest of spaces and typically include a radio module for wireless communication. This complexity can become a real challenge for
developers of IoT devices. Highly sensitive oscilloscopes with multi-domain capability are extremely helpful during optimisation and commissioning of these components, explains Guido Schulze, product manager for oscilloscopes at Rohde & Schwarz in Munich
W
hen debugging IoT modules, all module functions must be tested, as
well as the interactions between individual functions and components. A multi- domain oscilloscope is needed in order to perform comprehensive measurements using only one test instrument. The latest generation of ‘scopes can be
used to test all the module’s sensor and control signals, along with its integrated data processing, radio module and power supply. Multi-domain capability enables time, frequency, protocol and logic analyses and establishes all time references. Via the oscilloscope’s analogue input channels, the user simultaneously sees the signal in the time and frequency domain and, if desired, the spectrogram. This makes it possible to perform effective debugging on the functional system level.
MEASUREMENTS ON A GSM IOT MODULE The Cinterion BGS2 GSM module from Gemalto represents a good example of complex embedded wireless design for machine-to-machine (M2M) applications. It connects a GSM radio module to a baseband processor, to the power supply management, to various serial interfaces for modem (UART based), inter- integrated circuits (I2
C) and multipurpose (GPIO), as well as to the clock source, flash
memory, a converter and an audio interface. The module is designed
for autonomous remote operation using a long- life battery. At minimal current drain, the module will provide data via the radio interface for years. Characterising the module’s power usage is therefore an important part of commissioning and optimisation. Key measurements include the dynamic response of the power supply during data transmission and during sleep mode. The current of the IoT module is
measured using the most sensitive current probe available, capable of resolving currents less than 1mA at a bandwidth of 120 MHz, with a maximum current of 5A. Precise current measurements are possible in conjunction with the unusually low-noise input stages of the oscilloscope. To prevent false results, the current probe has to be demagnetised before measuring the current. In addition, the current probe and measurement channel need to be auto-zeroed to ensure that the lowest currents are measured accurately. Radio antenna signals are captured in this example via a near-field probe
Measurements on the ‘Cinterion BGS2’ GSM module from Gemalto
connected to the analogue input channel on the oscilloscope. Radio signals from the module are viewed as an analogue signal in both time and frequency domains via a fast Fourier transform (FFT). A further oscilloscope channel is connected to the power supply via an active voltage probe. Digital channels (MSO) then capture the communications at the modem interface. Individual UART serial bus signals are decoded with the RTO-K1 option. Some power supply measurements
require more detailed analysis. For example, this module exhibits a dynamic transition from sleep mode with very low current of 1-2mA, to an operational state with currents greater than 1A. Switching to 16-bit high definition mode, adjustable low-pass filters are applied to the signal after the A/D
Minimum current drain in sleep mode 32 SEPTEMBER 2016 | INSTRUMENTATION
Minimum current drain when not in sleep mode
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