Oscilloscope Basics: Setting Up FFTs

Figure 1: Capture time determines the
frequency resolution, Δf.

For most of their history, oscilloscopes have been thought of chiefly as a time-domain instrument. That is, an oscilloscope facilitates the observation of changes in a signal's amplitude over time. However, many modern digital and mixed-signal oscilloscopes provide spectral analysis capabilities based on fast Fourier transforms (FFTs) that convert a time-domain waveform into the frequency domain. There are lots of good reasons for taking advantage of this capability. Perhaps the most important is to gain insight into characteristics of the signal that simply are not apparent from a time-domain perspective.

Waveform Generators, Arbitrary and Otherwise

Figure 1: Teledyne LeCroy's ArbStudio 1104 is a four-channel,
16-bit arbitrary waveform generator with a maximum interpolated
sampling rate of 1 GS/s.

Next to an oscilloscope and perhaps a digital multimeter, a waveform generator is one of the most versatile and useful pieces of test equipment on the bench. Often, a device or circuit under test will require some kind of signal stimuli with which to confirm proper function and/or ferret out faults. This can run the gamut from a simple swept sine or pulse waveform for purposes of characterizing signal response, to advanced serial-data protocols, and even to the playback of analog signals captured in the real world. A waveform generator is your ticket to creating the required stimuli for your device or circuit under test.