Maximising the performance and potential of your oscilloscope

October 21, 2019 //By Cliff Ortmeyer
If there is one tool that is practically essential for electronic design, it is the oscilloscope. The oscilloscope makes it possible to look inside a circuit and see how it is really performing.

If there are signal-integrity issues or glitches affecting the operation of the circuitry, they will most likely show up on the screen of an oscilloscope. But to ensure correct results, it is vital to ensure that the signal going into the probe is as high quality as possible. Distortions caused by poor choices over probe selection and attachment can easily mislead the engineer and you do not want to be debugging part of a design when the bug is actually an artefact of the probing rather than the design itself.

Like the instruments to which they are attached, probes are examples of precision engineering that ensure the signal you see on the screen is as accurate as possible. It is easy to think of probes measuring voltage on a signal line at a particular point and having no effect on the signal itself, however, probes become part of the circuit under test, and introduce resistive, capacitive and inductive loading that can affect circuit behaviour. With careful control, this impact can be minimised to ensure the signal is only subtly affected.

For the most accurate results, the goal is to select a probe with the most appropriate loading for the circuit-under-test to minimise unwanted interactions and enable you to access all of the power, features and capabilities of your oscilloscope.


Choosing the right probe: passive, active or logic?

An important starting point is the choice of appropriate probe type. Probes for high-performance oscilloscopes can be categorised as passive and active, with subdivisions into special-purpose probes for taking differential measurements, connecting to logic buses and high-power lines.

The passive probe is a good general-purpose option for measuring a variety of signal types and voltage levels. The passive probe, as its name suggests, has no active electronics and will impose some level of loading on the circuit under test, but, it is often the most affordable solution and the pairing of a passive voltage probe with a current probe will provide a good option for measuring power in many situations.

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