Cathode Ray Oscilloscope and Digital Storage Oscilloscope

Published: 2019-06-24 14:07:59
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An oscilloscope is an instrument used in the laboratory to display and analyze the waveform of electronic signals. It shows an alternating current waveform. The frequency can be low up to 1 hertz and high-end ones displaying signals with frequencies to hundreds of gigahertz. The oscilloscope draws a graph of the instantaneous signal voltage against time. The positive figures are plotted upward while negative ones downward. The display is broken into two: horizontal divisions and vertical divisions. It normally has the horizontal sweep and vertical deflation measured in time per division and volts per division respectively. Its graph shows sine wave at the top while ramp wave at the bottom. Cathode ray oscilloscope and digital ray oscilloscope are the two main types of oscilloscope that are normally used in laboratories. Their comparison and contrast are given below.

Comparison between Cathode Ray Oscilloscope and Digital Storage Oscilloscope.


They both display lines that are crisscrossed called graticule. The graticule has major sub-divisions that are seen in the entire display. They scribe themselves on the x-y axes. The 54600A has ten major divisions and five minor divisions scribed per major division, thus each minor division counts as 0.2 of the major division. (Haas, 2007). The divisions are a reference point from which the absolute and relative measurements are made.

They both measure voltage against time. They analyze waveforms of electromagnetic signals. Oscilloscopes are used to observe the change of an electrical signal over time, such that voltage and time describe a shape that is continuously graphed against a calibrated scale. The observed waveform can be analyzed for such properties as amplitude, frequency, rise time, time interval and distortion. (Herrick, 1980). They display a graph that is plotted voltage against time to determine the waveform. Measured in hertz as the S.I Units, they can also be measured in megahertz and gigahertz.

Both CRO and DSO allow one to display phase shift, the rise in time and the fall in time. The delay, the pulse, the width, duty cycle, frequencies, and periods are also shown.

In both oscilloscopes, the scope controls are categorized into three areas namely vertical subsystem, horizontal subsystem and the trigger section. The vertical subsystem is used to control how voltage is scaled and how the signals move up and down on the y-axis. The horizontal oscilloscope controls the scale. Also how the signals move left and right on the x-axis. The trigger section controls at which point in a given time the oscilloscope will begin to display the signal. Its role is to ensure that the repetitive waveform displays are consistent.


Cathode Ray Oscilloscope (CRO) is analog and the unknown signals are amplified then applied to the Y axis of the display tube. On the x-axis, it shows a calibrated saw-toothed time base signal. This is synchronized to show the voltage against time on the display. On the other hand, the Digital Storage Oscilloscope (DSO) is digital such that it digitizes the unknown signal at a very fast rate through a high speed alternating current. The data displayed is in a digital memory that is in turn displayed on a digital screen.

Cathode Ray Oscilloscope has a trigger that is used to start the sweep. It is called a triggered sweep. Before the trigger, one cannot see what is happening unless if it is in the untriggered mode. Sometimes the trace can disappear along with the phosphor. However the Digital Storage Oscilloscope the sweep trigger is replaced with consecutive samples that are in series form and of a high-speed digitizer. The samples go into the memory and when full the processor will read the memory and show on the display. The sampling is consecutive means that if you are running at 1GS/s, you get a new sample point every 1ns. In a single shot, you get an entire waveform. If you had a 1000 point memory that means you could display 1us of continuous time on your screen. (Smith & Middleton, 2009). They also noted that if one wants to store more time, you get a scope with a large memory or drop the sample rate. This makes the DSO much desirable than CRO.

CRO make use of continually voltages that vary while the DSO uses binary numbers that correspond to the samples of voltage. Waveforms are noted as a series of the samples. They are stored and accumulated until when is enough then order to describe waveform. DSO uses digital memory, and can store data for very long time without degradation. Also, it enables complex processing of signals with use of high-speed digital processing. This is as opposed to then CRO that process the data in analog form. In the book, Modern Handbook Oscilloscope Middleton argued that the vertical input is digitized by an analog to digital converter to create a data set that is stored in the memory of a microprocessor. Making it the most efficient oscilloscope to use as opposed to CRO. (Middleton, 1980).

Why Digital Storage Oscilloscope over Cathode Ray Oscilloscope

They process complex signals using a very high-speed processor. They use digital memory, which stores data for a long time. This complex signals cannot be processed using the analog oscilloscopes.

It is easy to export data to Personal Computers Software. These softwares include spreadsheets, word processors, numerical analysis software together with tailored software.

DSOs are fast in displaying the waveform. They have the ability to control an instrument by running a program on the Personal computer and therefore the ability for automating tests. This makes them be fast in processing data.

DSOs have large and high-resolution color displays. The displays are much clear making them easier to read compared to displays shown by CROs. The Color is used to differentiate waveforms. More information is also displayed. Simultaneous alternative views of the waveform are shown and also automatic measurements of the waveform

Oscilloscopes are therefore used in the fields of sciences, medicine, and engineering. Telecommunications industry also uses than to a greater extent. Many improvements have been made on the oscilloscopes, and the digital oscilloscopes are mostly used because of their many advantages that come with them.


Bierman, H., Bierman, P., & Turner, R. (1981). Practical oscilloscope handbook. Rochelle Park, N.J.: Hayden Book Co.

Haas, A. (1958). Oscilloscope techniques. New York, New Delhi: Gernsback Library, Oxford and IBH.

Herrick, C. (1974). Oscilloscope handbook. Reston, Va.: Reston Pub. Co.

Middleton, R. (1979). Modern oscilloscope handbook. Reston, Va.: Reston Pub. Co.

Middleton, R. (1980). Troubleshooting with the oscilloscope. Indianapolis, Ind.: H.W. Sams.

Smith, P., & Middleton, R. (1974). Know your oscilloscope. Indianapolis: H.W. Sams.

Zwick, G. (1969). The oscilloscope. Blue Ridge Summit, Pa.: G/L Tab Books.


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