What exactly is an oscilloscope, anyway? Quite simply, an oscilloscope is a diagnostic instrument that draws a graph of an electrical signal. This simple graph can tell you many things about a signal, such as:

Nearly all consumer products today have electronic circuits. Whether a product is simple or complex, if it includes electronic components, the design, verification, and debugging process requires an oscilloscope to analyze the numerous electrical signals that make the product come to life.

The Oscilloscope’s Graph

1. The time and voltage values of a signal.
2. The frequency of an oscillating signal.
3. The “moving parts” of a circuit represented by the signal.
4. The frequency with which a particular portion of the signal occurs relative to other portions.
5. Whether or not a malfunctioning component is distorting the signal.
6. How much of a signal is direct current (DC) or alternating current (AC).
7. How much of the signal is noise and whether the noise is changing with time.

The Significance of Signal Integrity

A key benefit of an oscilloscope is its ability to accurately reconstruct a signal. The better the reconstruction of the signal the higher the signal integrity. Here’s one way to think of signal integrity. An oscilloscope is analogous to a camera that captures signal images that you then observe and interpret. Several key issues lie at the heart of signal integrity:

• When you take a picture, is it an accurate representation of what actually happened?
• Is the picture clear or fuzzy?
• How many accurate pictures can you take per second?

The Differences of Signal Integrity

The different systems and performance capabilities of an oscilloscope contribute to its ability to deliver the highest signal integrity possible. Probes also affect the signal integrity of a measurement system.

This primer helps you understand all of these elements so you can choose and use the oscilloscope appropriate for your application. Before you begin evaluating oscilloscopes, you need to understand the basics of waveforms and waveform measurements.

This information is covered in this chapter. It’s the foundation of putting an oscilloscope to work for you.

Understanding Waveforms and Waveform Measurementsy

The generic term for a pattern that repeats over time is a wave. Sound waves, brain waves, ocean waves,and voltage waves are all repetitive patterns. An oscilloscope measures voltage waves. A waveform is a graphic representation of a wave.

Physical phenomena such as vibrations, temperature, or electrical phenomena such as current or power can be converted to a voltage by a sensor. One cycle of a wave is the portion of the wave that repeats. A voltage waveform shows time on the horizontal axis and voltage on the vertical axis.

Waveform shapes reveal a great deal about a signal. Any time you see a change in the height of the waveform, you know the voltage has changed. Any time there is a flat horizontal line, you know that there is no change for that length of time.

Straight, diagonal lines mean a linear change; a rise or fall of voltage at a steady rate. Sharp angles on a waveform indicate sudden change. Figure 4 shows common waveforms.

Types of Waves

You can classify most waves into these types:

• Sine waves.
• Square and rectangular waves.
• Sawtooth and triangle waves.
• Step and pulse shapes.
• Periodic and non-periodic signals.
• Synchronous and asynchronous signals.
• Complex waves.

Next we’ll look at each of these types of waves.

Sine Waves

The sine wave is the fundamental wave shape for several reasons. It has harmonious mathematical properties”€it is the same sine shape you may have studied in trigonometry class.

The voltage in a wall outlet varies as a sine wave. Test signals produced by the oscillator circuit of a signal generator are often sine waves.

Most AC power sources produce sine waves (AC signifies alternating current, although the voltage alternates too; DC stands for direct current, which means a steady current and voltage, such as a battery produces.) The damped sine wave is a special case you may see in a circuit that oscillates, but winds down over time.