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What is an Oscilloscope: basics & fundamentals

The oscilloscope is one of the most useful test instruments used for electronic circuit design, electronics manufacture, test, service, and repair.

Some Oscilloscope Tutorials

Oscilloscope Basics

Oscilloscopes help us measure various parameters, such as voltage, analog and digital signals, and noise.

Modern oscilloscopes also have a huge number of additional functions which are useful for an electronic engineer or technician.

Almost every oscilloscope you encounter for sale today will be a Digital Storage Oscilloscope (DSO) or a Mixed Signal Oscilloscope (MSO). A mixed signal oscilloscope is a digital storage oscilloscope with additional functionality that integrates logic analyser capabilities. Some models will also perform an FFT, giving measurements in the frequency domain.

Either style of an oscilloscope is a fantastic diagnostic tool when troubleshooting a circuit. You can see the exact waveform of your circuit with millivolt resolution, and with some oscilloscopes, picosecond resolution. This makes it possible to catch short transient spikes from sensors, encoders or circuits that a multimeter can’t catch reliably. It also allows you to view digital signals, inspect the quality of edge transitions and view ringing or other signal integrity issues.

Oscilloscope Channels

Oscilloscopes have multiple channels. Therefore you can monitor the waveform going into a circuit, as well as the waveform coming out which makes it perfect for monitoring analog filters, amplifiers and other analog circuits.

Suppose you’re primarily working with digital signals. In that case, oscilloscopes are fantastic tools for you too – you can one channel watching one signal, for example, a button, and then see a microcontroller’s response to that input – such as a transmission over SPI or I2C. With the precise timings of an oscilloscope, you can measure how long your code is taking to execute or react to an interrupt.

Mixed Signal Oscilloscopes take this a step further, integrating a logic analyser that can give you many digital channels of input to monitor alongside the analog channels.

The name oscilloscope, comes from the fact that it enables oscillations to be viewed. Sometimes the name cathode-ray oscilloscope, or CRO was used. The reason for this was that cathode ray tubes (CRT) were used to display the waveforms.

Today, LCDs, or plasma displays are used as they are smaller, and more convenient to use, especially as the do not require the very high voltages of the old CRTs.

Function of an oscilloscope

The function of an oscilloscope is to be able to display waveforms on some form of display. In the normal mode of operation time is displayed along the X-axis (horizontal axis) and amplitude is displayed along the Y axis (vertical axis).

In this way it is possible to see an electronic waveform on an oscilloscope as it may be envisaged. The waveform could be likened to that of the ripples on travelling along the surface of a pond when a stone is dropped into it.

By seeing a waveform in this manner it is possible to see analyse the operation of the circuit and discover why any problems may exist.

When looking at oscilloscope there are several key topics and areas of interest:

Types of oscilloscope: There are several different types of oscilloscope from analogue to digital and more. The first types of oscilloscope were analogue, but with the advances in digital technology, virtually all new test instruments these days are processor controlled and use digital signal processing to provide excellent displays of the waveforms.
Not only are there oscilloscopes contained in standard bench style boxes, but some scopes are designed to link to computers, using their display and processing to assist. Often they are USB oscilloscopes, connected via USB links but other types are also available linked via other bus systems or for use within rack systems like PXI and the older VXI systems.
Scope specifications: The specifications for oscilloscopes can sometimes be confusing. A basic understanding of the terms and what they mean is very useful. Understanding the basic oscilloscope specifications can provide an understanding of the limitations of any given test instrument and also help in the selection when one needs to be hired, bought or even booked out of a common store.
The scope specifications are slightly different between the analogue and digital scopes.
Although basic concepts like accuracy, time base range, upper frequencies and the like are essentially the same, digital scopes also have specifications to items like the number of DAC bits, memory depth and the like that are specific to digital oscilloscopes.