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Choosing the right scope (Part 1)

Posted: 03 Oct 2011 ?? ?Print Version ?Bookmark and Share

Keywords:oscilloscope? accuracy? Gaussian frequency response?

Various oscilloscope specifications determine the accuracy with which signals can be captured and measured. However, an oscilloscope's primary specification is its bandwidth. So what do we mean by "bandwidth"? All oscilloscopes exhibit a low-pass frequency response that rolls-off at higher frequencies. Most scopes with bandwidth specifications of 1GHz and below typically have what is called a Gaussian frequency response, which approximates the characteristics of a single-pole low-pass filter. The lowest frequency at which the input signal is attenuated by 3 dB is considered the scope's bandwidth. Signal attenuation at the C3 dB frequency translates into approximately C30% amplitude error. In other words, if you input a 1 Vp-p, 100MHz sine wave into a 100MHz bandwidth oscilloscope, the measured peak-to-peak voltage using this scope would be in the range of 700 mVp-p (C3 dB = 20 Log (0.707/1.0). So you cannot expect to make accurate measurements on signals that have significant frequencies near your scope's bandwidth.

View the PDF document for more information.

Originally published by Agilent Technologies Inc. at as "Oscilloscope Selection Tip 1: Bandwidth".

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