Top 10 Criteria to Consider When Selecting an Oscilloscope (Part 1)

The oscilloscope is one of those general purpose pieces of test equipment that you can find in almost every electronics lab. Over the past few decades, the oscilloscope has evolved from analog to digital to mixed-signal and, most recently, to mixed-domain. There are as many opinions on the most important criteria for selecting an oscilloscope as there are manufacturers, so MATsolutions has distilled the information down to these 10 important factors.

Bandwidth & rise time are critical for determining signal shape and capturing fast transitions

Bandwidth determines the highest frequency content of a signal that your oscilloscope can capture and measure accurately. Be sure to select an instrument with a bandwidth that is at least 5 times higher than the highest frequency content you want to measure. This will help to capture up to the fifth harmonic, which is critical to determine the shape of the digital signal.

For digital signals, rise time is also important - look for an oscilloscope with rise time that is at least 5 times faster than the rise time of your signals. This will help to capture fast transitions more accurately.

Sample rates provide digital signal details

Sample rate is how often an oscilloscope samples the signal. The higher the sample rate, the more details you have of the signal. As with Nyquist’s Sampling Theorem, the sample rate should be higher than the frequency of the signal. However, unlike Nyquist’s Sampling Theorem, due to the filter roll-off in the oscilloscope, the sampling rate should be at least 5 times higher than the signal.

Probes must be supported by the oscilloscope

Having an oscilloscope with sufficient bandwidth and sample rate is futile if the probe becomes a bottleneck to the system bandwidth or, worse still, if you cannot physically reach the measurement point. If the probe bandwidth is less than the oscilloscope bandwidth, the probe bandwidth becomes the limiting factor. If the probe does not have the right kind of tip or form factor to access the measurement points, you will not be able to make any measurements. Therefore, it is important to look at an oscilloscope that can support probes that meet your requirements. Look for as large a portfolio of probes as possible, with variety of probe tip heads (or at least the one that you intend to use). Also, confirm that the probes do not overload your circuit and alter its characteristics.

Sufficient acquisition memory allows performance up to the maximum sample rate

Acquisition Memory = Time Span x Sample Rate

Basically, what that means is the oscilloscope needs sufficient memory to sustain the high sample rate or to capture longer signal duration - oscilloscopes do not always perform up to the maximum sample rate unless there is a sufficient memory. In general, the deeper the memory the better. But, do find out how the oscilloscope manages the deep memory. As the oscilloscope has to handle more processing of more data, its responsiveness can be affected.

The number of input channels must match your measurements

Oscilloscopes typically come with 2 or 4 analog channels and optionally another 8 or 16 digital channel for mixed-signal. Mixed-domain oscilloscopes provide an additional RF input. This requirement is pretty straight-forward – you just simply need to confirm that there are enough input channels to match your measurements.

Continue reading to learn about  5 more criteria to consider when looking for an oscilloscope. In the meantime, you can browse our website for oscilloscopes that we have in inventory or talk to MAT to get some sound advice on choosing one.