Oscilloscope Types

- each different type of oscilloscope has its own advantages and disadvantages. To choose a scope for a given application it is necessary to know what is available.

An oscilloscope is one of the major tools available for testing electronic circuitry. The oscilloscope is able to display waveforms and as a result it gives a particularly useful view of what is happening in an electronic circuit. While the basic philosophy behind all oscilloscopes is the same, there are a number of different variants that are available, each possessing slightly different capabilities and being suited for a given application or set of applications.

Oscilloscopes fall into a variety of categories. The biggest distinction is whether they are analogue or digital, but within the digital oscilloscope arena there are ordinary digital oscilloscopes, digital storage oscilloscopes, digital phosphor oscilloscopes, and digital sampling oscilloscopes.

Analogue oscilloscope

The analogue oscilloscope of the original type of oscilloscope. As the name implies it uses analogue techniques throughout to create the pattern on the display. Typically they use a cathode ray tube where the voltages on the x and y plats cause a dot on the screen to move. In the horizontal direction this is controlled by the time base, whereas in the vertical direction the deflection is proportional to the signal input. Essentially the signal is amplified and applied to the Y plates of the cathode ray tube using analogue technology.

Although this technology is now very dated, they are still used in some circles.   Read more about the Analogue Oscilloscope

Digital oscilloscopes

The concept behind the digital oscilloscope is somewhat different to an analogue scope. Rather than processing the signals in an analogue fashion, this type of scope converts the signal into a digital format using an analogue to digital converter and then processes the signals digitally. With digital signal processing hardware and software becoming more powerful, this enables the processing of the signals to be undertaken in a far more flexible manner, and enables many additional features to be included within the scope. Updates and additional functionality can then be made by simply upgrading the software or firmware within the scope

Image of an oscilloscope used for wide variety of test applications

There are several different types of digital oscilloscope that can be encountered. With many manufacturers trying to gain an edge on their competitors, new names tend to be developed to try to bring over the new levels of functionality and features.

  • Digital oscilloscope / Digital Storage Oscilloscope, DSO :   The boundary between these two types of oscilloscopes has become very indistinct in recent years. Originally te storage scopes, DSO had additional memory to enable the storage of waveforms. Now most scopes have memory incorporated as standard, the only difference being the size. As a result, both names are often used to describe the same instrument, and therefore they are now virtually synonymous. The digital scope or digital storage scope is now the basic type of oscilloscope used, containing all the basic functions expected these days.  Read more about the Digital Oscilloscope
  • Digital Phosphor Oscilloscope:   The digital phosphor oscilloscope (DPO) is a highly versatile form of oscilloscope that uses a parallel processing architecture to enable it to capture and display signals under circumstances that may not be possible using a standard DSO.     Read more about the Digital Phosphor Oscilloscope
  • Digital Sampling Oscilloscopes:  

    These oscilloscopes are used for analyzing very high frequency signals. They are used for looking at repetitive signals which are higher than the sample rate of the scope. They collect the samples by assembling samples from several successive waveforms, and by assembling them during the processing, they are able to build up a picture of the waveform. In this way these oscilloscopes may be able to view signals at frequencies up to 50 GHz and more.   Read more about the Digital Sampling Oscilloscope

  • Mixed Domain Oscilloscope, MDO:   As the name implies, the mixed domain oscilloscope is able to operate in more than one domain, i.e. in time to display waveforms and in frequency to display signal spectra. This type of oscilloscope is very useful for developing RF systems where fault finding in both domains is needed. It is in valuable in locating issues where waveforms may give rise to unwanted or unusual spectrum issues. As a result these scopes are finding increasing popularity for the development of cellular systems as well as Wi-Fi, and the many other wireless systems in use today.
  • Mixed Signal Oscilloscope, MSO :   This type of oscilloscope combines an oscilloscope function with that of a logic analyser. This enables in depth investigations to be made of logic circuits. With digital and processor controlled systems becoming more complex, there has been a growing need to be able to analyse the signals on these boards and systems in more depth and with greater levels of functionality. The MSO enables logic transitions and states to be analysed in conjunction with oscilloscope types of display or the signal waveforms.   Read more about the Mixed Signal Oscilloscope

Other approaches

Oscilloscopes are widely used in industry and they are taking advantage of the huge levels of processing power that are now available. While most oscilloscopes are dedicated instruments, a growing number of scopes are being sold that incorporate a PC to provide the processing power. As PCs are widely available this considerably reduces the cost of buying a high performance oscilloscope.

  • USB oscilloscope:   One particular variant of this approach that has become very popular is what is often termed the USB oscilloscope. As the name implies, the USB oscilloscope interfaces with a PC using the USB connector. This provides an effective interface for communication between the two elements.   Read more about the USB Oscilloscope

While this type of approach may not be suitable in many applications it is ideal for many others where a general purpose PC can be used. Even so dedicated oscilloscopes are being increasingly used as they now offer better performance levels than ever before.

By Ian Poole

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