1094-6969/06/$20.00©2006IEEEDecember 2006 IEEE Instrumentation & Measurement Magazine 27

The History and Technology of Oscilloscopes

An overview of its primary characteristics and working principles

Oscilloscopes are one of the main tools for analyz-ing electrical signals. The primary informationobtained from the waveform of the signal isvisualization of its amplitude variation over

time. Oscilloscopes are excellent tools for testing, debug-ging, and troubleshooting because they can easily detectwaveforms and demonstrate if the elec-trical components or circuit modulesare working properly. Oscilloscopesalso provide support during the designof new electronic circuits. In addition to electrical signals,other physical or chemical quantities can be measured byusing different probes that have been developed into anappropriate transducer.

Even if the basic philosophy of every oscilloscope’s work-

ing principle is the same there are two main types of oscillo-scopes: analog and digital.

The aim of this article is to provide an overview of themain characteristics of the different types of oscilloscopesand correlate their evolution with the development of theunderlying technologies they incorporate.

IntroductionAndré-Eugène Blondel was a Frenchphysicist who was born on 28 August

1863. He is known as the inventor of the electromagneticoscillograph, a device that enabled the observation of alter-nating signals. The first oscillographs traced an ink recordon a moving paper chart with a pen arm attached to a mov-ing coil. As a consequence of the working principle based

J. Miguel Dias Pereira

PHOTOS: NASA GLENN RESEARCH CENTER (NASA-GRC) & GRID PATTERN- © DIGITAL VISION

28 IEEE Instrumentation & Measurement Magazine December 2006

on a set of mechanical devices, the first oscillographs had avery low bandwidth in the range of 10–19 Hz.

The first evolution of these instruments came with thedevelopment of light-beam oscillographs. In these instru-ments, there was still a moving coil but this coil was attachedto a mirror and a light beam was reflected onto a movingphotographic film. With these instruments, the mechanicalbandwidth restrictions were a little bit reduced and the band-width increased to 500 Hz.

Some years later, in 1897, Karl Ferdinand Braun inventedthe cathode ray tube (CRT). The British company A.C.Cossor (later acquired by Raytheon) designed the first dualbeam oscilloscope in the late 1930s. It applied an oscillatingreference signal to horizontal deflector plates and the inputmeasured signal to the vertical deflector plates. Images oftransient electrical signals were then obtained on a smallphosphor screen.

In 1946, Howard C. Vollum and Jack Murdock inventedthe triggered oscilloscope that synchronizes the graphicalrepresentation of repetitive signal waveforms. Since then,and especially after the Tektronix [1] foundation, the majorityof oscilloscope manufacturers [2]–[8] have technicallyimproved their products. Bandwidth and accuracy have con-tinuously increased, first with analog oscilloscopes and laterwith digital sampling oscilloscopes that enable measurementof bandwidths in the range of tens of gigahertz.

Oscilloscopes became an essential instrument to supporttechnological development in all engineering areas. Digitaltechnology associated with digital phosphor oscilloscopesenables the measurement of statistical data (e.g., jitter) thatwere unavailable some years ago. Now oscilloscopes enablemany more functions than a simple representation of timevarying signals; digital signal processing techniques areadding new functionalities of spectrum and logic analyzersto modern oscilloscopes.

A few words must also be dedicated to the role of oscillo-scopes in teaching activities. It is difficult to find a morecomplete instrument for didactic purposes. Analog and digi-tal versions of oscilloscopes are by themselves a completestudy case for several electrical engineering subjects includ-ing signal conditioning, analog-to-digital conversion, analogsignal processing, digital signal processing, and communica-tion protocols (e.g., RS232, USB, GPIB and Ethernet).Modern oscilloscopes can also be connected to a network forprinting, file sharing, Internet access, and advanced commu-nication functions like sending e-mails triggered by pro-grammed events.

Oscilloscope Functional BlocksTo simplify the description, I have chosen to explain a classicalanalog oscilloscope with a vector display unit based on a CRT.Basically, an oscilloscope performs the following main functions:

◗ acquisition of the input electrical signal◗ signal conditioning (attenuation/amplification) ◗ synchronization tasks that provide a stable representa-

tion of the input signal

◗ visualization of the signal waveform in the display unit ◗ the ability to measure and analyze the electrical signal

and to store or print the measurement results. The hardware block diagram includes typically five func-

tional blocks: ◗ vertical channel◗ horizontal channel◗ time basis◗ trigger◗ display unit.Acquisition of the electrical signal is performed by the

vertical channel of the oscilloscope that contains the electri-cal interface circuits and amplifiers. They are used to get thecorrect amplitude of the signals that are delivered to the hor-izontal deflector plates of the CRT.

The horizontal channel generates a signal that is appliedto the vertical deflector plates of the CRT. This signal has asaw-toothed waveform when the instrument is to provide thetemporal representation of the acquired input signal (Y) or ithas an arbitrary waveform from the external input (X), whenthe oscilloscope is used in the X-Y representation mode.

The oscilloscope time basis unit contains the circuits thatgenerate the saw-toothed waveform, which provide the hori-zontal sweep of the CRT electronic beam. The time basis alsoprovides a blanking pulse to extinguish the electronic beambetween sweep intervals, during which the waveform is dis-played. Without the blanking pulse, the return of the elec-tronic beam, from the right edge to the left edge of thedisplay, would be visible by the user.

The trigger unit contains a set of circuits that generatesthe timing signals to synchronize the start of sweep withtiming pulses generated from the input signal (internaltrigger) or from an external signal (external trigger). Thistriggering function is essential to achieve a stable image inthe display unit. Without triggering, multiple copies ofthe waveform are drawn in different places on the dis-play, giving an incoherent jumble or a moving image onthe screen.

As an example, Figure 1 represents a periodic input sig-nal (y), the sweep signal (sw), and the waveform displayedin the CRT unit. The trigger threshold has zero amplitudeand a positive edge-trigger set-up and the hold-off time isequal to the signal period (T). The sweep signal has a periodthree times the input signal period (TH = 3T) and the sweepspeed is equal to T/5 s/div, assuming a display unit withthe typical ten divisions in the horizontal time axis.

The synchronization between input and sweep signals,implemented by the trigger circuits, is essential to obtain astable image on the screen, which means multiple sweepswith the same waveform. The synchronization is stillobtained as long as the input signal is repetitive, not neces-sarily periodic, and has a minimum update rate.

The oscilloscope display unit was initially a CRT wherethe waveforms become visible due to the impact of the elec-tronic beam on a fluorescent and phosphorescent coatingmaterial. Currently, the CRT display units are being

December 2006 IEEE Instrumentation & Measurement Magazine 29

replaced by the thin film transistor liquid crystal display(TFT LCD) [9]. These displays can achieve high brightness atlow drive voltages and current densities, which result inmore compact units with a lower power consumption.

Oscilloscope TypesOscilloscopes can be either analog or digital. There are still alarge number of analog oscilloscopes in use, but they arebeing gradually replaced by digital oscilloscopes. Much likePCs, the cost of digital oscilloscopes is dropping, and theyare using the latest, low-cost, electronic developments incomponents. Equivalent time-sampling techniques are usedin the sampling oscilloscope to extend the bandwidth when-ever repetitive and stable high frequency signals are mea-sured. Digital phosphor oscilloscopes enable therepresentation of an electrical signal in three dimensions,time, amplitude, and amplitude over time, using an almostreal-time screen update rate. Virtual oscilloscopes based ondata acquisition boards or sound cards are also an attractivesolution for a large number of applications since they use thehardware and software already available in PCs.

Analog OscilloscopesThe main hardware blocks of an analog oscilloscope includeone or multiple vertical channels, the horizontal channel, thetime basis, the trigger circuit, and the CRT unit where sig-nals’ waveforms are displayed. The vertical channel includesa compensated attenuator, a preamplifier, a delay circuit,and a final vertical amplifier that boost the input signal to alevel adequate for the vertical sensitivity of the CRT unit.

The horizontal channel can be used in two different oper-ating modes: internal and external. In both operating modes,it includes a final horizontal amplifier that boosts the outputsignal to a level adequate for the horizontal sensitivity of theCRT unit. If working in internal mode, the input signal is asaw-toothed waveform generated by the oscilloscope’s timebasis. If working in external mode, the input signal is anyexternal signal that passes through a compensated attenua-tor and a preamplifier.

The time basis includes mainly a set of flip-flops, an inte-grator, and circuits for summing and inversion; it generatesthe saw-toothed signal used by the horizontal channel when itis working in internal operating mode. It is important to notethat the start of the ramp contained in a saw-toothed signal istriggered by internal or external events, but when the rampsignal reaches its maximum amplitude, that corresponds tothe positioning of the electronic beam at the right edge of thedisplay. The electronic beam is blocked by applying a nega-tive voltage to the Wehnelt (W) cylinder of the CRT.

The trigger circuit includes a slope selector, a trigger flip-flop, and a derivative circuit. The slope selector selects thepositive or the negative edge trigger for a given triggeramplitude. The trigger flip-flop is a Schmitt-trigger circuitthat outputs a rectangular waveform synchronized with trig-ger events. Control of trigger level is provided by varyingthe transition voltages of the Schmitt trigger. And finally, the

output trigger pulse that must define the start of sweepsaccurately is obtained from the output of a derivative circuit.

The CRT is a special kind of vacuum tube that containsan electron gun, a set of vertical and horizontal deflectorplates (mentioned previously), several electronic lenses,anodes, and a display internally coated with a fluorescentand phosphorescent coating material. Figure 2 represents asimplified version of the hardware block diagram of an ana-log oscilloscope.

Figure 3 is an old model of a didactic oscilloscope fromSiemens [10] that has its electrical schematic diagram displayedon the front panel. This laboratory oscilloscope provides easyaccess to multiple internal signals. It is possible to simultane-ously display the external input signal and multiple test-pointsignals of the main internal circuits of the oscilloscope.

Typically the bandwidth of an analog oscilloscopes is in thehundreds of megahertz and the main limitation is the CRT dis-play unit. These devices can be used to display rapidly varyingsignals in real time since there is no digitalization, memorybuffering, or any kind of signal processing between the inputsignal and the output display unit. The acquired signal is dis-played continuously with only negligible delays that arecaused by the hardware components of the electrical circuits.

Digital OscilloscopesIt is typical to divide digital oscilloscope into three maincategories:

◗ digital storage oscilloscope (DStO) that uses real-timesampling techniques

◗ digital sampling oscilloscope (DSaO) that uses equiva-lent time sampling techniques

◗ digital phosphor oscilloscope (DPO) that uses advancedsignal and image processing techniques.

The following is an explanation of each category accord-ing to its working principle.

Fig. 1. (a) Oscilloscope input (y) and sweep (sw) signals and (b) waveformdisplayed in the CRT unit.

t

y

0 T 2T 3T

t TH

Display Unit

swTriggerHold Off

(a)

(b)

30 IEEE Instrumentation & Measurement Magazine December 2006

DSOs

DSOs became possible with the technological evolution ofhybrid analog-to-digital converters (ADCs) that were fastand accurate enough to digitize high-frequency signals, thedevelopment of memories that could store input data as fastas it was sampled and the development of compact, low-power, and accurate raster display units.

Digital oscilloscopes use ADCs and represent data inter-nally in a digital format. Waveforms are sampled, and thosevalues are stored until a complete waveform is acquired.There are many advantages associated with a digital repre-sentation of data. To mention only some of them:

◗ the capability to store transient events and display thempermanently, without need of special persistence tubesor photographic set-ups

◗ the advantage of digital data storage, in magneticperipheral units, for future analysis

◗ the capability to implement data processing algorithmsto access additional measurement information, forexample, the signal spectrum by using fast Fouriertransform (FFT) algorithms

◗ the improvement of signal transmission capabilitiesprovided by the digital I/O communication ports(RS232, USB, GPIB, and Ethernet between others).

The functional blocks of these oscilloscopes include acompensated attenuator and a vertical amplifier that trans-lates the input signal range to a voltage interval that must beincluded in the ADC’s input voltage range. A simplifiedfunctional block is represented in Figure 4. The ADC per-forms the analog-to-digital conversion for single or multiple

Fig. 2. Hardware block diagram of an analog oscilloscope.

PreAmp.

FinalAmp.Delay

VerticalChannel

Display

PreAmp.

FinalAmp.Xinput

Yinput

HorizontalChannel

CRT

Foc.

Ast.

Int.

Zinput

Pos.

Xext

Sweep Generator Manual

−1

Stab.

Return F/F

IntegratorCommand

F/F W

k

Trigger

Trigger F/F

Derivative Circuit

Level

ExternalTrigger

TriggerAmp.Pos.

Xint

0 Freq.

0

uv

ug

us

uq

uc

ur

ud

Slope

Attenuator

Σ

+−

Attenuator

December 2006 IEEE Instrumentation & Measurement Magazine 31

input channels. Generally the ADC is preceded by a sample-and-hold circuit that assures a constant voltage level at itsoutput for each sample during analog-to-digital conversionof that sample.

In low-cost models, there is a single ADC shared byall input channels but the effective bandwidth of theoscilloscope depends on the number of active channelsand the circuit must also include additional multiplexerand demultiplexer circuits, before and after the ADC. Ifthere are multiple ADCs, it is possible to extend oscillo-scope bandwidth below the Nyquist rate by using inter-leaving techniques [11]–[13] . In this case, theanalog-to-digital conversion of a single channel is per-formed by multiples of ADCs, usually two, four, oreight, and the samples are then ordered according totheir temporal sequence.

The microprocessor unit controls all the functionalblocks and performs multiple data processing tasks. Thereare two memory blocks. The acquisition memory, MemAcq ,stores digitized samples during the acquisition cycle, andthe display memory, MemDisp , stores a complete record ofsamples to be displayed. With the use of digital-to-analogconverters (DACs), it is still possible to use CRTs as displayunits, but these oscilloscopes generally incorporate rasterdisplay units.

The main advantages of using two different memoryblocks are

◗ minimizing “blind acquisition periods,” which aretimes the oscilloscope doesn’t acquire the input signal

◗ enabling a screen update rate higher than the inputsampling rate.

As before, the trigger circuit supports internal or externaltriggering modes and includes a time base, a trigger com-parator, a delay counter, and a stop acquisition block.Bandwidth specifications of these oscilloscopes working inthe real-time sampling mode are determined by the maxi-mum signal sampling rate and associated Nyquist rate, con-sidering that there are no additional bandwidth restrictionscaused by the input channel amplifier or compensation cir-cuits. For example, if the ADC has a maximum sampling rateof 100 MS/s and is dedicated to a single channel, the band-width usually specified by the manufacturer is half the maxi-mum sampling rate, which means for this example a50-MHz bandwidth. However, this is a limit that only makessense for data processing applications, since the recovery of

Fig. 3. Didactic oscilloscope from Siemens.

Fig. 4. Hardware block diagram of a digital storage oscilloscope.

Y1input

Attenuator Vert. Amp. S and H ADC MemAcq

Y2input

Attenuator Vert. Amp. S and H ADC

µP Raster Display

Ext. Trig

AttenuatorTrig.

Comp.Delay

Counter StopAcq.

Time Base

MemAcq

MemDisp

32 IEEE Instrumentation & Measurement Magazine December 2006

an analog signal is assured as long as the sampling rate is atleast twice the maximum frequency value contained in thesignal bandwidth. However, for time and amplitude analy-sis of sampled signals it is usual to consider a minimum of25 samples per signal period (N). However this limitdepends on the required amplitude accuracy and on theinterpolation method used for signal representation.

Figure 5 represents the linear interpolation relative erroras a function of the number of samples per period for N = 4,8, 16, 32, or 64. The relative error is evaluated using as refer-ence the peak-to-peak amplitude of a sinusoidal input signaland the time units are normalized to signal period.

The interpolation error decreases with N and its maxi-mum value is lower than 1% for N = 16. By performing

some additional calculations, it ispossible to verify that the maxi-mum relative error for N = 25 isabout 0.39%. This means a value ofalmost 50 dB in terms of an associ-ated signal-to-noise ratio. This isthe signal-to-noise quantizationratio of an ADC with 8 bits. So, thismeans that the linear interpolationerror for N = 25 is almost equal tothe quantization error of a typical8-bit ADC in terms of maximumerror amplitude.

Finally, to compare the errorsfor different interpolation meth-ods, Figure 6 represents thoseerrors for linear, cubic, and cubicspline interpolation methods whenthe oversampling factor (N) isequal to 25. Previous results showclearly that interpolation perfor-mance increases at the expense ofthe required computational loadof their implementation.

If the sinc function (sin(πx)/πx)is used for interpolation, the resultsin this case are even better.However, the disadvantage of thisapproach is that the results dependon the assumption that the signal isband limited, but in practical terms,with a finite number of pulses it isnot possible to assure that condi-tion and the results obtained withspline interpolation are smootherand generally more accurate thanthe results obtained with sinc func-tion interpolation.

The bandwidth of a DStO isdependent on the maximum sam-pling rate of the ADC. However,using equivalent time samplingtechniques it is possible to captureand display signals with frequen-cies much higher than the maxi-mum sampling rate for the ADC[14], [15]. The hardware blocks ofthese oscilloscopes are very similarto the ones that are used in DStOs.Fig. 6. Relative errors obtained with different interpolation techniques with an oversampling factor equal to 25.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

10−8

10−6

10−4

10−2

100

Time (n.u.)

Rel

ativ

e E

rror

(%

)

Linear

CubicSpline

Cubic

Fig. 5. Linear interpolation relative error as a function of the number of samples per period for N = 4, 8,16, 32, 64.

0 0.5 1

10−4

10−3

10−2

10−1

100

101

102

Time (n.u.)

Rel

ativ

e E

rror

(%

)

N=4

N=64

N=16

N=8

N=32

December 2006 IEEE Instrumentation & Measurement Magazine 33

DSaOsIn a DSaO, an accurate sampling bridge is inserted beforeperforming any signal attenuation or amplification, due tosampling rate restrictions [16], [17]. The equivalent timesampling method can only be applied to repetitive wave-forms and not to single-shot events. Repetitive samplingtechniques capture data from multiple occurrences of theinput signal waveform. A set of points are acquired on eachoccurrence of the trigger event and after multiple triggerevents the signal samples are ordered according to their timesequence. Since the data are not acquired in real time, in asingle sweep, Nyquist criteria does not apply and the band-width of sampling oscilloscopes is larger than the limitimposed by ADC’s maximum sampling rate.

Equivalent time sampling can be implemented in twodifferent ways: sequential and random sampling. Insequential sampling mode, the capture delay after the trig-ger event is sequentially incremented after each acquisi-tion cycle and a samples’ ordering algorithm is notrequired, since the sampling sequence preserves the sig-nal’s waveform time sequence. However, this samplingmode enables only post-trigger acquisitions since all thesamples are taken after the trigger event.

Figure 7 represents an illustration of the timing diagramsassociated with the sequential equiva-lent time sampling technique. In thisexample, a single sample is takenafter a time delay that is incrementedwith the occurrences of the successivetrigger events.

In random equivalent time sam-pling, the sampling is done con-stantly, not waiting for a triggerevent. After the occurrence of multi-ple acquisition cycles, the sampledpoints are ordered by measuringthe amount of time that elapsedbetween it and the trigger event.The sampled data are captured before and after the trigger;it is possible to represent samples before the trigger event(pretriggering) or before and after the trigger event (abouttrigger). Obviously, in this case, ordering the task is morecomplex since the sampling sequence does not preservethe signal’s waveform time sequence.

The bandwidth specifications of these oscilloscopes aremainly dependent on the accuracy and resolution of thesampling timing circuits. Considering a minimum numberof samples per period equal to N, the required timing accu-racy must be lower than:

�t ≤ 1N · LB

where LB represents the oscilloscope bandwidth.Figure 8 is a graphical representation of the previous rela-

tionship for N = 8, 16, 25, and 32. The time units are in psand the bandwidth units in gigahertz.

Currently, the upper bandwidth limit is in the order ofsome tens of gigahertz, which means a timing accuracy andresolution better than a few picoseconds. However, it isimportant to note that this bandwidth is obtained at theexpense of a reduced dynamic range since there is no attenu-ator/amplifier before the sampling bridge. The dynamicrange of sampling oscilloscopes is usually limited to 1 V ofpeak-to-peak amplitude.

DPOsThe technology evolution that supported the appearing ofDPOs was the development of powerful microcontrollers, theincrement of integration scale in VLSI devices and the develop-ment of application specific integrated circuits (ASICs). DPOsdisplay signals in three dimensions: time, amplitude, andamplitude over time. Each cell of the database screen that isassociated with a single pixel in the oscilloscope screen is rein-forced with intensity information each time the waveformimage activates that cell. Doing so, the DPO translates probabil-ity density function (PDF) data into displayed colors and inten-sities. These oscilloscopes include simultaneous advantagesover analog and DStO enabling an extended number of auto-mated measurements capabilities: amplitude, time, area, phase,burst, histograms, and communication measurements.

Fig. 7. Illustration of the timing diagrams associated with the sequential equivalent time sampling technique.

Triggert

1

2 3 4

51

2 4

5t

3

Trigger

Fig. 8. Sampling timing requirements of DSaO as a function of bandwidthand number of samples per period N = 8, 16, 25, 32.

5 10 15 20 25 30 35 400

5

10

15

20

25

∆t (

ps)

LB (GHz)

N=8N=16N=25

N=32

34 IEEE Instrumentation & Measurement Magazine December 2006

The DPOs include unique ASIC components thatacquire waveform images and explore parallel processingarchitectures to increase the display updating rate. A sim-plified version of the vertical channel block diagram of aDPO is represented in Figure 9. Relative to the DStO blockdiagram, the main differences appear after the ADC block.A DStO processes captured waveforms serially and evenwith very high-speed ADCs the speed of the microproces-sor unit limits the display update rate. The parallel archi-tecture of the DPO enables a direct copy of sampled datafrom acquisition to display memory without delays. Signaldetails, transient events, and other dynamic characteristicsof the signal are captured and displayed in real time with-out loss of information caused by “blind” acquisition peri-ods. The DPO microprocessors for acquisition and displaywork in parallel with the acquisition and display units,respectively, without restricting acquisition process anddisplay update rate.

Virtual OscilloscopesCurrently, a substantial number of oscilloscopes are basedon PCs taking advantage of the potential of their hardwareand software components. This approach is an acceptablesolution for a large number of applications and PCadvanced signal processing modules can be used to obtainmore measurement information than provided by stand-alone oscilloscopes.

Data acquisition (DAQ) circuit boards are now availablefrom many manufacturers and can be internally or externallyconnected to any desktop or laptop computer. Graphicalprogramming languages are generally used to develop dedi-cated software modules for data acquisition, processing, andrepresentation. These virtual oscilloscopes are cheaper andmore flexible than the traditional versions, and such virtualinstruments are becoming popular in common applicationsthat don’t require hard specifications. Advanced processingtasks of measurement data can use a set of programs that areusually installed in every PC. Beside this advantage, thecommunication through local area networks (LANs) and theInternet is automatically assured by the communicationports of the PC, and data analysis, storage and transmissionare easily implemented in a user friendly way.

As an example, Figure 10 represents the front panel of aLabVIEW virtual instrument (VI), running a VISA applica-tion of a Tektronix oscilloscope that is connected to a PCthrough a GPIB channel [18], [19]. It is important to note thatin this case the software modules developed in LabVIEWcan access new functionalities that are not provided by thestand-alone oscilloscope.

There are also some solutions of virtual oscilloscopesbased on PC sound cards [20], [21]. The performances areobviously reduced but there is no additional price to pay asFig. 10. Virtual oscilloscope front panel developed in LabVIEW.

Fig. 9. Simplified version of the vertical channel block diagram of a DPO.

Vin

MemAcq MemDisp

Display

µProc.Acq

µProc.Disp

µProc.ContIntegrated Acquisition/Display

Unit

Attenuator Vert. Amp. S and H

ADC

December 2006 IEEE Instrumentation & Measurement Magazine 35

long as the PC already includes a sound card. The main limi-tations of these virtual oscilloscopes are mainly associatedwith low values of the input voltage dynamic range, inputimpedance and bandwidth, typically lower than 20 kHz. Animportant note is that several oscilloscope simulators can bedownloaded from the Internet that give some help in stu-dent activities [22], [23].

ConclusionsThis article gives an overview of the primary characteristicsand working principles of oscilloscopes. Starting from themechanical and light-beam oscillographs, the technologicaldevelopment associated with CRT devices and later withsemiconductor integrated circuits creates the basic infras-tructure for analog oscilloscopes. The next step in the field ofoscilloscope evolution is associated with digitalization andsignal processing.

Digital oscilloscopes store waveforms in digital format andpresent a large number of advantages that are inherent to sig-nal digitalization. Some of these advantages are new measure-ment capabilities provided by digital signal processingtechniques, and the transmission capabilities supported bydifferent communication protocols. The continuous develop-ment in electronic technology, namely in VLSI devices, sam-pling bridges, microprocessors and raster display units, hasincreased the performance of oscilloscope devices. They madeit possible to capture very high frequency signals with DSaOand using DPO to represent signals in three dimensionsalmost in real-time and without “blind” acquisition periods.

Even now with the advent of PCs and the developmentof high-speed and high-resolution data acquisition boards,together with dedicated software modules, it is possible todevelop PC based oscilloscopes with increasing performanceand new capabilities that can easily be integrated in a userfriendly and flexible software application.

In the near future, the development of virtual instrumentsand the new capabilities provided by microprocessors, DSPsand other electronic devices will support the development ofnew instruments with extended capabilities that will combinethe specific functionalities of oscilloscopes, spectrum analyz-ers and logic analyzers in a single instrument.

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[Online]. Available: http://www.chauvin-arnoux.com [5] Kenwood TMI Corporation, oscilloscopes index [Online].

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[8] Iwatsu oscilloscopes [Online]. Available:

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[14] Tektronix, Application Note. Real-time versus equivalent-time

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[18] LabVIEW - The software that powers virtual instrumentation

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[19] National instruments VISA - products and services [Online].

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oscilloscope.com

J. Miguel Dias Pereira (joseper@est.ips.pt) receiveddegrees in electrical engineering from the InstitutoSuperior Técnico (IST) of the Technical University ofLisbon (UTL) in 1982. During almost eight years heworked for Portugal Telecom in digital switching andtransmission systems. In 1992, he returned to teaching asassistant professor in Escola Superior de Tecnologia ofInstituto Politécnico de Setúbal, where he is, at present, acoordinator professor. In 1995 he received the M.Sc. degreeand in 1999 the Ph.D. degree in electrical engineering andcomputer science from IST. His main research interests areincluded in the instrumentation and measurements areas.He is a Senior Member of the IEEE.