Basic Oscilloscope Fundamentals

Introduction

Electronic technology permeates our lives. Millions of people use electronic devices such as cell phones, televisions, and computers on a daily basis. As electronic technology has advanced, the speeds at which these devices operate have accelerated. Today, most devices use high-speed digital technologies. 

Engineers need the ability to accurately design and test the components in their high-speed digital devices. The instrumentation engineers use to design and test their components must be particularly well-suited to deal with high speeds and high frequencies. An oscilloscope is an example of just such an instrument. 

Oscilloscopes are powerful tools that are useful for designing and testing electronic devices. They are vital in determining which components of a system are behaving correctly and which are malfunctioning. They can also help you determine whether or not a newly designed component behaves the way you intended. Oscilloscopes are far more powerful than multimeters because they allow you to see what the electronic signals actually look like. 

Oscilloscopes are used in a wide range of fields, from the automotive industry to university research laboratories, to the aerospace-defense industry. Companies rely on oscilloscopes to help them uncover defects and produce fully-functional products. 

Electronic Signals 

The main purpose of an oscilloscope is to display electronic signals. By viewing signals displayed on an oscilloscope, you can determine whether a component of an electronic system is behaving properly. So, to understand how an oscilloscope operates, it is important to understand the basic signal theory. 

Wave properties 

Electronic signals are waves or pulses. Basic properties of waves include the following. 

Amplitude 

Two main definitions for amplitude are commonly used in engineering applications. The first is often referred to as the peak amplitude and is defined as the magnitude of the maximum displacement of a disturbance. The second is called the root-mean-square (RMS) amplitude. To calculate the RMS voltage of a waveform, square the waveform, find its average voltage and take the square root. 

For a sine wave, the RMS amplitude is equal to 0.707 times the peak amplitude. 

Phase shift

Phase shift refers to the amount of horizontal translation between two otherwise identical waves. It is measured in degrees or radians. For a sine wave, one cycle is represented by 360 degrees. Therefore, if two sine waves differ by half of a cycle, their relative phase shift is 180 degrees. 

Period 

The period of a wave is simply the amount of time it takes for a wave to repeat itself. It is measured in units of seconds. 

Frequency 

Every periodic wave has a frequency. The frequency is simply the number of times a wave repeats itself within one second (if you are working in units of Hertz). The frequency is also the reciprocal of the period. 

Waveforms 

A waveform is the shape or representation of a wave. Waveforms can provide you with a great deal of information about your signal. For example, it can tell you if the voltage changes suddenly, varies linearly, or remains constant. There are many standard waveforms, but this section will cover the ones you will encounter most frequently. 

Sine waves 

Sine waves are typically associated with alternating current (AC) sources such as an electrical outlet in your house. A sine wave does not always have a constant peak amplitude. If the peak amplitude continually decreases as time progresses, we call the waveform a damped sine wave. 

Square/rectangular waves 

A square waveform periodically jumps between two different values such that the lengths of the high and low segments are equivalent. A rectangular waveform differs in that the lengths of the high and low segments are not equal. 

Triangular/sawtooth waves 

In a triangular wave, the voltage varies linearly with time. The edges are called ramps because the waveform is either ramping up or ramping down to certain voltages. A sawtooth wave looks similar in that either the front or back edge has a linear voltage response with time. However, the opposite edge has an almost immediate drop.