Picture the heart rate monitor that you always see next to hospital beds on “House” or “Grey’s Anatomy.” You hold your breath as you wait for the next beep and jump of the line on the screen, and you dread the flat line as the TV show reaches its apex.
Well, when my family asks me what I do for a living, this is how I describe an oscilloscope. But instead of displaying the signal of a human heart, oscilloscopes show the heartbeat of electronic devices. They give us all kinds of insights into whether or not an electronic device is operating correctly, allowing us to check its vitals.
The vitals of our devices could be voltage or current. And just like we don’t want our hearts to beat too fast or too slow, we want those voltages to oscillate at the right pace or frequency. We all know heart murmurs are bad. Well, we don’t want any glitches in our electrical signals either, and an oscilloscope can help us find them. Having insights like this into your electronic devices allows you to validate it is operating as expected. And if it’s not, oscilloscopes help you diagnose the problem and correct it. If you are an electrical engineer, chances are you could use an oscilloscope ─ whether you’re a test engineer or student or work in manufacturing, repair, research, or development.
The basic operation of an oscilloscope displays voltage versus time, with voltage on the vertical axis and time on the horizontal axis. This allows you to double check that your device’s signal is as you expect, both in magnitude and frequency. And because oscilloscopes provide a visual representation of the signal, you can view any anomalies or distortion that might be occurring. But before you start testing, there are some things for you to consider.
Oscilloscopes come in many flavors. You want to select an oscilloscope with the right bandwidth, signal integrity, sample rate, and channel inputs. You also want to make sure it is compatible with any applications and probes you may need. Here is a list of some of the features you should check when deciding what oscilloscope to use:
- Bandwidth – The range of frequencies the oscilloscope can measure accurately. Oscilloscope bandwidths typically range from 50 MHz to 100 GHz.
- Sample Rate – The number of samples the oscilloscope can acquire per second. The greater the samples per second, the more clearly and accurately the waveform is displayed.
- Signal Integrity – The oscilloscope’s ability to represent the waveform accurately. This is a topic I’m particularly passionate about and you’ll find me writing about this a lot. You wouldn’t want a heart rate monitor that displays incorrect information. It would do no good to declare a patient dead whose heart is still beating. The same is true for your device under test. You wouldn’t want to declare your device is malfunctioning and spend weeks trying to find the root cause when there isn’t actually a problem.
- Channels – The input to the oscilloscope. They can be analog or digital. There are typically 2 to 4 analog channels per oscilloscope.
- Probe Compatibility – A probe is the tool used connect the oscilloscope to your device under test. There are a large variety of passive and active probes, each made for specific use cases. You want an oscilloscope that is compatible with the type of probe you need for your specific tests.
- Applications – Signal analysis, protocol decode, and compliance test software can greatly reduce the time it takes to identify and capture errors in your designs. Analysis software can help you find and evaluate jitter, perform Fourier transforms, create eye diagrams, and even identify and quantify crosstalk. Protocol decoding software can identify digital packets of information, trigger on different packet conditions, and identify protocol errors. Not all oscilloscopes are compatible with every application.
What are Oscilloscopes Used for?
Now that you’re armed with the lingo, you’re ready to get going. The most basic testing only requires an oscilloscope with 50 to 200 MHz of bandwidth, a passive probe, and sufficient sample rate, signal integrity, and channel inputs.
Armed with these basics, you can spot-check your printed circuit boards (PCBs) to find faulty parts, noisy power lines, shorts, and I/Os (inputs and outputs) that are not working; dive into different trigger modes to search for runts, glitches, and timing errors; and capture signals and data to prove the quality of your designs. Some basic oscilloscopes even provide Bode or frequency and phase response analysis. And this is just the start.
Oscilloscopes are versatile and widely used instruments. Automotive technicians use oscilloscopes to diagnose electrical problems in cars. University labs use oscilloscopes to teach students about electronics. Research groups all over the world have oscilloscopes at their disposal. Cell phone manufacturers use oscilloscopes to test the integrity of their signals. The military and aviation industries use oscilloscopes to test radar communication systems. R&D engineers use oscilloscopes to test and design new technologies. Oscilloscopes are also used for compliance testing such as USB and CAN protocols where the output must meet certain standards.
Now that you know what an oscilloscope is and some of the crucial oscilloscope specs, it’s time to get testing. So throw on your scrubs (or maybe an ESD strap instead) and get started!
To learn more about how to operate an oscilloscope and understand measurement fundamentals, you can read the Basic Oscilloscope Fundamentals application note.