What is an Oscilloscope?

For those who work in education, design, service, maintenance, field service or quality control, an oscilloscope is the most important tool in meeting measurement challenges. Sometimes referred to as a scope, this instrument displays graphical representations of electrical signals. In most applications the graph shows how signals change over time; the vertical axis represents voltage and the horizontal represents time. The usefulness of an oscilloscope is not limited to the world of electronics. With the proper transducer, an oscilloscope can measure all kinds of phenomena. Due to the endless variations in performance and price, selecting the right oscilloscope is an important, yet daunting task.

Choosing an Oscilloscope

Considering the right oscilloscope is a matter of analyzing your present and future needs. Are your signals repetitive or single shot? Will you need to store and view the signals? What is the bandwidth of the signals you need to capture? How many signals do you need to display simultaneously? The answers to these questions will determine the type of scope you need. Repeat this mantra– speed, accuracy and safety.

And now, in the ring, analog vs. digital! In this debate, it boils down to real-time or application needs. An analog oscilloscope gives an immediate picture of the waveform on the screen while a digital samples the waveform and uses an ADC to reconstruct it on the screen. Some say they like the real-time capabilities of analog scopes, but there’s no denying the overwhelming popularity of digital. Because of their high bandwidth, single shot ability, color displays and portable design, digital oscilloscopes offer increased measurement capacity and virtually unlimited functionality.

If you’re going digital, then there are additional specifications to consider– sample rate and waveform capture rate. A DSO’s sample rate is specified in Samples per Second and indicates how frequently the scope samples the input signal. The waveform capture rate denotes how fast the scope can process acquired information after each trigger event and reset the trigger for another acquisition. When either sample rate or waveform capture rate are inadequate, important signal details can be missed.

Bandwidth and budget go hand-in-hand. Since more bandwidth usually means more money, you’ll want to evaluate the frequency of the signal you are measuring. Bandwidth determines an oscilloscope’s fundamental ability to measure a signal. The analog bandwidth must be higher than the maximum frequency that you wish to measure. Trying to look at a signal that’s too fast for a scope’s bandwidth will introduce errors in amplitude and/or time-interval measurements. Without adequate bandwidth, all the features, bells and whistles in your oscilloscope will mean nothing. A good rule for determining your bandwidth requirement is the “5 times rule”: multiply the highest frequency component of the signals you want to examine by 5.

Channel your needs. The number of channels you require depends on your applications. Two channel scopes are popular for economical and general-purpose troubleshooting. If you want to view the relationship of several analog signals, then four channels are necessary.

Easy there, Trigger! An oscilloscope’s trigger function synchronizes the horizontal sweep at the correct point of the signal, essential for clear signal characterization.

Trigger controls allow you to stabilize repetitive waveforms and capture single-shot waveforms. Horizontal trigger position control is only available on digital oscilloscopes and allows you to capture what a signal did before a trigger event, known as pre-trigger viewing. Pre-trigger viewing is a valuable troubleshooting aid allowing you to record the events that led up to the problem.

You’re only as good as your probe. The right probes matched to the oscilloscope and the device-under-test (DUT) not only allow the signal to be brought to the oscilloscope cleanly, they also amplify and preserve the signal for the greatest signal integrity and measurement accuracy. To ensure accurate reconstruction of your signal, choose a probe that, when paired with your oscilloscope, exceeds the signal bandwidth by 5 times.

The Next Generation of Oscilloscopes

Since new technologies and standards continue to roll out in every industry, dramatic changes in signaling and users’ testing needs are driving the oscilloscope trends. The objective is to give customers the necessary performance to confront a higher level of signal integrity issues along with a suite of tools to accelerate their products’ development. These days, typical high-end oscilloscopes now connect to personal computers for display, use software to control sweep rate, have a battery power option, offer usability with all popular operating platforms and can display several waveforms simultaneously. The trends of more buttons and menus are being reversed to make scopes easier to use, while high-resolution color monitors allow for optimum visibility. Oscilloscopes have come a long way and the latest advancements are creating resourceful and confident engineers throughout the design and test cycle.