A&D Series 57ZZ Manual de usuario descargar pdf (Pagina 14)

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.

Figure 15 shows examples of sine and damped sine

waves.

Square and Rectangular Waves

The square wave is another common wave shape.

Basically, a square wave is a voltage that turns on

and off (or goes high and low) at regular intervals. It’s

a standard wave for testing amplifiers – good ampli-

fiers increase the amplitude of a square wave with

minimum distortion. Television, radio, and

computer circuitry often use square waves for timing

signals.

The rectangular wave is like the square wave except

that the high and low time intervals are not of equal

length. It is particularly important when analyzing

digital circuitry.

Figure 16 shows examples of square and rectangular

waves.

Sawtooth and Triangle Waves

Sawtooth and triangle waves result from circuits

designed to control voltages linearly, such as the

horizontal sweep of an analog oscilloscope or the

raster scan of a television. The transitions between

voltage levels of these waves change at a constant

rate. These transitions are called ramps.

Figure 17 shows examples of sawtooth and triangle

waves.

Step and Pulse Shape

Signals such as steps and pulses that only occur

once are called single-shot or transient signals. The

step indicates a sudden change in voltage, like what

you would see if you turned on a power switch. The

pulse indicates what you would see if you turned a

power switch on and then off again. It might repre-

sent one bit of information traveling through a

computer circuit or it might be a glitch (a defect) in a

circuit.

A collection of pulses travelling together creates a

pulse train. Digital components in a computer

communicate with each other using pulses. Pulses

are also common in x-ray and communications

equipment.

Figure 18 shows examples of step and pulse shapes

and a pulse train.

Complex Waves

Some waveforms combine the characteristics of

sines, squares, steps, and pulses to produce a wave-

shape that challenges many oscilloscopes. The signal

information may be embedded in the form of ampli-

tude, phase, and/or frequency variations. For

example, look at Figure 19 – although it’s an ordi-

nary composite video signal, it is made up of many

cycles of higher-frequency waveforms embedded in a

lower-frequency “envelope.” In this example it’s

usually most important to understand the relative

levels and timing relationships of the steps. What’s

needed to view this signal is an oscilloscope that

captures the low-frequency envelope and blends in

the higher-frequency waves in an intensity-graded

fashion so you can see their overall level.

Analog instruments and DPOs are most suited to

viewing complex waves such as video signals. Their

displays provide the necessary intensity grading.

Often, the frequency-of-occurrence information that

their displays express is essential to understanding

what the waveform is really doing.

Figure 15. Sine and damped sine waves.

Figure 16. Square and rectangular waves.

Figure 17. Sawtooth and triangle waves.

Figure 18. Step, pulse, and pulse train shapes.

Figure 19. Complex wave (NTSC composite video signal).

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