What types of waves does an oscilloscope have?

You can divide most waves into the following categories:

■Sine wave

■Square wave and rectangular wave

■Sawtooth wave and triangle wave

■Step and pulse shapes

■Periodic and non-periodic signals

■Synchronous signal and asynchronous signal

■Compound Wave

Sine Wave

The sine wave is a fundamental waveform for many reasons. It has a harmonious mathematical quality, and you may have learned about the same sinusoidal shape when you were teaching triangles. The voltage at a wall outlet varies in a sinusoidal manner. The signal generated by the oscillator circuit of a signal generator is usually a sine wave. Most AC power supplies generate sine waves. (AC stands for alternating current, and of course the voltage also alternates. DC stands for direct current, and means a steady current and voltage, such as that generated by a battery.) A damped sine wave is a special case you might see in a circuit, which oscillates but tapers off over time.

Square wave and rectangular wave

The square wave is another common waveform. Basically, a square wave is a voltage that switches on and off (or goes high and low) at regular intervals. It is a standard wave used for amplifier testing, and a good amplifier will boost the amplitude of a square wave with minimal distortion. Television, radio, and computer circuits often use square waves in timing signals. A rectangular wave is similar to a square wave, but the high and low intervals are of unequal length. Rectangular waves are particularly important when analyzing digital circuits.

Sawtooth and triangle waves

Sawtooth and triangle waves come from circuits designed for linearly controlled voltages, such as the horizontal sweep of an analog oscilloscope or the raster sweep of a television. These waves have transitions between voltage levels that change at a constant rate. These transitions are called ramps.

Step and pulse shapes

Signals that occur infrequently or non-regularly, such as steps and pulses, are called single-shot signals or transient signals. A step is a sudden change in voltage, similar to the voltage change you see when you turn on a power switch.

A pulse is a sudden change in voltage, similar to the change in voltage you see when you turn a power switch on and then off. A pulse can represent a single bit of information traveling through a computer circuit, or it can be a glitch or defect in the circuit. A collection of pulses traveling together is called a pulse train. Digital devices in a computer use pulses to communicate with each other. These pulses can be in the form of a serial data stream or they can use multiple signal lines to represent values ​​in a parallel data bus. Pulses are also common in X-ray, radar, and communications equipment.

Periodic and non-periodic signals

A signal that repeats is called a periodic signal, and a signal that changes over time is called a non-periodic signal. A still photo can be compared to a periodic signal, while an animation is equivalent to a non-periodic signal.

Synchronous and asynchronous signals

When there is a timing relationship between two signals, they are called synchronous signals. The clock, data, and address signals inside a computer are all synchronous signals. Asynchronous signals are used to describe signals that do not have a timing relationship between them. Since touching a key on a computer keyboard has no timing relationship with the clock inside the computer, these actions are considered asynchronous signals.

Composite Wave

Some waveforms combine features of sine waves, square waves, steps, and pulses to create complex waveforms. The signal information can be embedded in the form of amplitude, phase, or frequency changes. For example, although the signal in Figure 6 is an ordinary composite video signal, it consists of multiple cycles of a high-frequency waveform embedded in a low-frequency envelope.

In this instance, it is usually most important to understand the relative level and timing relationship between the steps. To observe this signal, you need a Tektronix oscilloscope that can capture the low frequency envelope, mixed into the high frequency wave in an intensity graded manner so that the overall combination can be seen as a visually interpreted image. Tektronix digital phosphor oscilloscopes are best suited for observing complex waves, such as video signals, as shown in Figure 6. Their display provides the necessary frequency of occurrence information, or intensity grading, which is critical to understanding the actual operation of the waveform.

Some Tektronix oscilloscopes allow certain complex waveform types to be displayed in specific ways. For example, telecommunications data can be displayed as an eye diagram or constellation diagram. Telecommunications digital data signals can be displayed on an oscilloscope as a special type of waveform called an eye diagram. The name eye diagram comes from the waveform's resemblance to a series of eyes, as shown in Figure 7. An eye diagram is generated when digital data from a receiver is sampled and applied to the vertical inputs, while the data rate is used to trigger the horizontal scan. The eye diagram displays the data for one bit or one unit interval with all possible edge transitions and states superimposed in one comprehensive view.

A constellation diagram represents a signal modulated by a digital modulation scheme, such as quadrature amplitude modulation or phase shift keying.