Challenges of de-bugging complex embedded systems

So what are the challenges facing engineers today working on IoT devices? 

The IoT design cycle will typically start off at the Chipset level, with designers selecting the most suitable from a features, performance and power requirement aspect. Since wireless is a certainty, moving to an embedded module makes design sense, for design speed cycle, cost and integration.

Here is a typical block diagram of an IoT Device, as you can see, the designer has many potential issues facing them, ranging from the DC Power aspect (which we covered previously), the various control signals whether they be analog or digital, high-speed serial data such as USB, SATA, DDR etc.. plus various RF issues from antenna design to a simple case of is my device actually transmitting!

As can be seen, IoT Challenges are not limited to just the time-domain.  RF testing is also a key requirement during the entire IoT development process.  RF Design and Debug is necessary to ensure all wireless communications signals are working as designed.  Issues caused by interference need to be identified and resolved.  There are also industry requirements before a product can ship.  New Devices must pass compliance testing, whether EMI/EMC or wireless technology compliance.   Having a measurement tool designed to help debug compliance issues is critical in reducing development time and costs associated with failed compliance tests.

The MDO4000C series of oscilloscopes are designed with RF design and debug in mind.  The dedicated spectrum analyzer is fully integrated into the oscilloscope architecture, enabling time-correlated measurements of analog, digital, and RF signals.  Advanced RF triggering and RF analysis displays provide quick, deep insight into your device functionality.  Additionally, offline software works in tandem with the oscilloscope for pre-compliance testing of wireless communication standards as well as EMI/EMC.

Let's take a look at how the ability to Time Correlate across multiple domains can aid the embedded designer ;

No Doubt, people are very familiar with the time domain view we see on the top portion of the display and likewise some people are very familiar with the frequency domain view we see on the bottom portion of the display. The key thing is how do we link the two together? If you look at the top portion, we call that analog time. That is the record length that you collected during a single shot acquisition. Old time would be on the far left, new time would be on the far right. What we have to do is introduce the concept of spectrum time. Because it is an FFT box, we have to have a start time and an end time for the FFT calculation and that is exactly what spectrum time is. When you are looking at this display here, you can see the small orange rectangle. That tells us when the spectrum that we are looking at happened. In this particular example, we can see that channel 1 (the yellow channel) is on a VCO enabled line…we can see the label there. Channel 2 is on a PLL controllable digital channel…that’s in cyan. The purple is the actual digital bus and in this case, we are carrying out an SPI decode. The spectrum analyzer is tuned to a centre frequency of 2.3 gigahertz with a span of 300 megs and a resolution bandwidth of 300 kilohertz.

The SPI bus (which we are actually triggering on) turns on a CW transmitter that should be transmitting at 2.4Ghz, we are monitoring the VCO Enable line on Channel 1 and the PLL Voltage on channel 2, as the PLL controllable digit changes from low to high, the output frequency of the transmitter is also going to change from low to high, I am going to play the animation and we’ll see how it works. As we step through spectrum time, we are also moving through analog time, and can see how the frequency was changing from low to high in correlation with the PLL Voltage. On the frequency domain, we see that we have an automatic marker that is tracking the peak signal in the display. In this way, we can fully time correlate the spectrum analyzer to the scope. Now, remember, it is not just an FFT on a scope channel, but it is an independent spectrum analyzer that has record length that is time correlated to the record length of the analog and digital channels.

As mentioned, the MDO4000C series oscilloscopes offer the ability to analyze analog, digital, and RF signals simultaneously, in real time.  This is exceptionally helpful in applications where RF output is linked to analog or digital control signals on your device.  The multi-domain display gives great insight as to changes in RF signals over time.  The wide capture bandwidth and additional analysis displays, like spectrogram, are powerful tools when identifying or characterizing interference within IoT devices. 

Tektronix MDO4024C Mixed Domain Oscilloscope, 200MHz, 4 analogue/16 digital channels – RS stock code (908-2828)

Tektronix MDO4034C Mixed Domain Oscilloscope, 350MHz, 4 analogue/16 digital channels – RS stock code (908-2837)

Tektronix MDO4054C Mixed Domain Oscilloscope, 500MHz, 4 analogue/16 digital channels – RS stock code (908-2830)

Tektronix MDO4104C Mixed Domain Oscilloscope, 1GHz, 4 analogue/16 digital channels – RS stock code (908-2834)