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A CDE Definition

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A test instrument that is used to measure and analyze electronic signals (waves and pulses) displayed on its screen. The x-axis represents time, and the y-axis represents an instantaneous view of the voltage of the input signal. To allow viewing signals across a wide frequency range, the rate and speed at which the sweep of the x-axis occurs is configurable. The sensitivity of the inputs can also be configured to accept signals from microvolts peak-to-peak to many thousands of volts peak-to-peak.

Both analog and digital oscilloscopes are available. In an analog scope, the x-axis is controlled by an internal time base, and the y-axis is directly controlled by the input signal. In a digital model, the input voltage is sampled at a preset frequency. The x-axis represents the samples along a timeline, and the y-axis shows the voltage levels of each sample. See spectrum analyzer.

Using an Oscilloscope
Oscilloscopes are used to examine the voltages on circuit boards, radios, TVs and countless electronic devices. This one is being used to test chips after manufacture. (Image courtesy of VLSI Technology, Inc.)

spectrum analyzer

A hardware device or software used to examine the frequency and power components of a signal. It provides more information than an oscilloscope, because it can display the signals over a range of frequencies. For example, whereas an oscilloscope would show total noise level, a spectrum analyzer would show the noise as related to frequency. Available in both analog and digital models, digital analyzers sample the incoming waveforms and convert them to fast fourier transforms (FFTs).

Bandwidth Resolution
The range of frequencies being analyzed is the "bandwidth," while the width of the individual samples is the "bandwidth resolution." In the following example, the bandwidth is 86 Hz to 20 kHz, and the bandwidth resolution is 40 Hz. Each sample represents a 40 Hz section of the displayed 19,914 Hz band. See oscilloscope.

An Audio Analysis
This example shows the power levels and frequencies of an audio signal as displayed in a software-based spectrum analyzer.

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