PHOTOS: NASA GLENN RESEARCH CENTER (NASA-GRC) & GRID PATTERN- © DIGITAL VISION The History and Technology of An overview of its primary characteristics and working principles

scilloscopes are one of the main tools for analyz- ing principle is the same there are two main types of oscillo- ing electrical signals. The primary information scopes: analog and digital. obtained from the waveform of the signal is The aim of this article is to provide an overview of the Ovisualization of its amplitude variation over main characteristics of the different types of oscilloscopes time. Oscilloscopes are excellent tools for testing, debug- and correlate their evolution with the development of the ging, and troubleshooting because they can easily detect underlying technologies they incorporate. waveforms and demonstrate if the elec- trical components or circuit modules J. Miguel Dias Pereira Introduction are working properly. Oscilloscopes André-Eugène Blondel was a French also provide support during the design physicist who was born on 28 August of new electronic circuits. In addition to electrical signals, 1863. He is known as the inventor of the electromagnetic other physical or chemical quantities can be measured by oscillograph, a device that enabled the observation of alter- using different probes that have been developed into an nating signals. The first oscillographs traced an ink record appropriate transducer. on a moving paper chart with a pen arm attached to a mov- Even if the basic philosophy of every ’s work- ing coil. As a consequence of the working principle based

December 2006 IEEE Instrumentation & Measurement Magazine 27 1094-6969/06/$20.00©2006IEEE on a set of mechanical devices, the first oscillographs had a ◗ visualization of the signal waveform in the display unit very low bandwidth in the range of 10–19 Hz. ◗ the ability to measure and analyze the electrical signal The first evolution of these instruments came with the and to store or print the measurement results. development of light-beam oscillographs. In these instru- The hardware block diagram includes typically five func- ments, there was still a moving coil but this coil was attached tional blocks: to a mirror and a light beam was reflected onto a moving ◗ vertical channel photographic film. With these instruments, the mechanical ◗ horizontal channel bandwidth restrictions were a little bit reduced and the band- ◗ time basis width increased to 500 Hz. ◗ trigger Some years later, in 1897, Karl Ferdinand Braun invented ◗ display unit. the cathode ray tube (CRT). The British company A.C. Acquisition of the electrical signal is performed by the Cossor (later acquired by Raytheon) designed the first dual vertical channel of the oscilloscope that contains the electri- beam oscilloscope in the late 1930s. It applied an oscillating cal interface circuits and . They are used to get the reference signal to horizontal deflector plates and the input correct amplitude of the signals that are delivered to the hor- measured signal to the vertical deflector plates. Images of izontal deflector plates of the CRT. transient electrical signals were then obtained on a small The horizontal channel generates a signal that is applied phosphor screen. to the vertical deflector plates of the CRT. This signal has a In 1946, Howard C. Vollum and Jack Murdock invented saw-toothed waveform when the instrument is to provide the the triggered oscilloscope that synchronizes the graphical temporal representation of the acquired input signal (Y) or it representation of repetitive signal waveforms. Since then, has an arbitrary waveform from the external input (X), when and especially after the [1] foundation, the majority the oscilloscope is used in the X-Y representation mode. of oscilloscope manufacturers [2]–[8] have technically The oscilloscope time basis unit contains the circuits that improved their products. Bandwidth and accuracy have con- generate the saw-toothed waveform, which provide the hori- tinuously increased, first with analog oscilloscopes and later zontal sweep of the CRT electronic beam. The time basis also with digital sampling oscilloscopes that enable measurement provides a blanking pulse to extinguish the electronic beam of bandwidths in the range of tens of gigahertz. between sweep intervals, during which the waveform is dis- Oscilloscopes became an essential instrument to support played. Without the blanking pulse, the return of the elec- technological development in all engineering areas. Digital tronic beam, from the right edge to the left edge of the technology associated with digital phosphor oscilloscopes display, would be visible by the user. enables the measurement of statistical data (e.g., jitter) that The trigger unit contains a set of circuits that generates were unavailable some years ago. Now oscilloscopes enable the timing signals to synchronize the start of sweep with many more functions than a simple representation of time timing pulses generated from the input signal (internal varying signals; digital signal processing techniques are trigger) or from an external signal (external trigger). This adding new functionalities of spectrum and logic analyzers triggering function is essential to achieve a stable image in to modern oscilloscopes. the display unit. Without triggering, multiple copies of A few words must also be dedicated to the role of oscillo- the waveform are drawn in different places on the dis- scopes in teaching activities. It is difficult to find a more play, giving an incoherent jumble or a moving image on complete instrument for didactic purposes. Analog and digi- the screen. tal versions of oscilloscopes are by themselves a complete As an example, Figure 1 represents a periodic input sig- study case for several electrical engineering subjects includ- nal (y), the sweep signal (sw), and the waveform displayed ing signal conditioning, analog-to-digital conversion, analog in the CRT unit. The trigger threshold has zero amplitude signal processing, digital signal processing, and communica- and a positive edge-trigger set-up and the hold-off time is tion protocols (e.g., RS232, USB, GPIB and Ethernet). equal to the signal period (T). The sweep signal has a period

Modern oscilloscopes can also be connected to a network for three times the input signal period (TH = 3T) and the sweep printing, file sharing, Internet access, and advanced commu- speed is equal to T/5 s/div, assuming a display unit with nication functions like sending e-mails triggered by pro- the typical ten divisions in the horizontal time axis. grammed events. The synchronization between input and sweep signals, implemented by the trigger circuits, is essential to obtain a Oscilloscope Functional Blocks stable image on the screen, which means multiple sweeps To simplify the description, I have chosen to explain a classical with the same waveform. The synchronization is still analog oscilloscope with a vector display unit based on a CRT. obtained as long as the input signal is repetitive, not neces- Basically, an oscilloscope performs the following main functions: sarily periodic, and has a minimum update rate. ◗ acquisition of the input electrical signal The oscilloscope display unit was initially a CRT where ◗ signal conditioning (attenuation/amplification) the waveforms become visible due to the impact of the elec- ◗ synchronization tasks that provide a stable representa- tronic beam on a fluorescent and phosphorescent coating tion of the input signal material. Currently, the CRT display units are being

28 IEEE Instrumentation & Measurement Magazine December 2006 replaced by the thin film transistor liquid crystal display output trigger pulse that must define the start of sweeps (TFT LCD) [9]. These displays can achieve high brightness at accurately is obtained from the output of a derivative circuit. low drive voltages and current densities, which result in The CRT is a special kind of vacuum tube that contains more compact units with a lower power consumption. an electron gun, a set of vertical and horizontal deflector plates (mentioned previously), several electronic lenses, Oscilloscope Types anodes, and a display internally coated with a fluorescent Oscilloscopes can be either analog or digital. There are still a and phosphorescent coating material. Figure 2 represents a large number of analog oscilloscopes in use, but they are simplified version of the hardware block diagram of an ana- being gradually replaced by digital oscilloscopes. Much like log oscilloscope. PCs, the cost of digital oscilloscopes is dropping, and they Figure 3 is an old model of a didactic oscilloscope from are using the latest, low-cost, electronic developments in Siemens [10] that has its electrical schematic diagram displayed components. Equivalent time-sampling techniques are used on the front panel. This laboratory oscilloscope provides easy in the sampling oscilloscope to extend the bandwidth when- access to multiple internal signals. It is possible to simultane- ever repetitive and stable high frequency signals are mea- ously display the external input signal and multiple test-point sured. Digital phosphor oscilloscopes enable the signals of the main internal circuits of the oscilloscope. representation of an electrical signal in three dimensions, Typically the bandwidth of an analog oscilloscopes is in the time, amplitude, and amplitude over time, using an almost hundreds of megahertz and the main limitation is the CRT dis- real-time screen update rate. Virtual oscilloscopes based on play unit. These devices can be used to display rapidly varying data acquisition boards or sound cards are also an attractive signals in real time since there is no digitalization, memory solution for a large number of applications since they use the buffering, or any kind of signal processing between the input hardware and software already available in PCs. signal and the output display unit. The acquired signal is dis- played continuously with only negligible delays that are Analog Oscilloscopes caused by the hardware components of the electrical circuits. The main hardware blocks of an analog oscilloscope include one or multiple vertical channels, the horizontal channel, the Digital Oscilloscopes time basis, the trigger circuit, and the CRT unit where sig- It is typical to divide digital oscilloscope into three main nals’ waveforms are displayed. The vertical channel includes categories: a compensated attenuator, a preamplifier, a delay circuit, ◗ digital storage oscilloscope (DStO) that uses real-time and a final vertical that boost the input signal to a sampling techniques level adequate for the vertical sensitivity of the CRT unit. ◗ digital sampling oscilloscope (DSaO) that uses equiva- The horizontal channel can be used in two different oper- lent time sampling techniques ating modes: internal and external. In both operating modes, ◗ digital phosphor oscilloscope (DPO) that uses advanced it includes a final horizontal amplifier that boosts the output signal and image processing techniques. signal to a level adequate for the horizontal sensitivity of the The following is an explanation of each category accord- CRT unit. If working in internal mode, the input signal is a ing to its working principle. saw-toothed waveform generated by the oscilloscope’s time basis. If working in external mode, the input signal is any external signal that passes through a compensated attenua- y tor and a preamplifier. The time basis includes mainly a set of flip-flops, an inte- grator, and circuits for summing and inversion; it generates 0 T2T3Tt the saw-toothed signal used by the horizontal channel when it sw is working in internal operating mode. It is important to note Tr igger that the start of the ramp contained in a saw-toothed signal is Hold Off triggered by internal or external events, but when the ramp TH t signal reaches its maximum amplitude, that corresponds to (a) the positioning of the electronic beam at the right edge of the display. 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- Display Unit flop, and a derivative circuit. The slope selector selects the positive or the negative edge trigger for a given trigger amplitude. The trigger flip-flop is a Schmitt-trigger circuit (b) that outputs a rectangular waveform synchronized with trig- ger events. Control of trigger level is provided by varying Fig. 1. (a) Oscilloscope input (y) and sweep (sw) signals and (b) waveform the transition voltages of the Schmitt trigger. And finally, the displayed in the CRT unit.

December 2006 IEEE Instrumentation & Measurement Magazine 29 DSOs ◗ the advantage of digital data storage, in magnetic DSOs became possible with the technological evolution of peripheral units, for future analysis hybrid analog-to-digital converters (ADCs) that were fast ◗ the capability to implement data processing algorithms and accurate enough to digitize high-frequency signals, the to access additional measurement information, for development of memories that could store input data as fast example, the signal spectrum by using fast Fourier as it was sampled and the development of compact, low- transform (FFT) algorithms power, and accurate raster display units. ◗ the improvement of signal transmission capabilities Digital oscilloscopes use ADCs and represent data inter- provided by the digital I/O communication ports nally in a digital format. Waveforms are sampled, and those (RS232, USB, GPIB, and Ethernet between others). values are stored until a complete waveform is acquired. The functional blocks of these oscilloscopes include a There are many advantages associated with a digital repre- compensated attenuator and a vertical amplifier that trans- sentation of data. To mention only some of them: lates the input signal range to a voltage interval that must be ◗ the capability to store transient events and display them included in the ADC’s input voltage range. A simplified permanently, without need of special persistence tubes functional block is represented in Figure 4. The ADC per- or photographic set-ups forms the analog-to-digital conversion for single or multiple

Pre Final Yinput Attenuator Delay Amp. Amp. Vertical Channel Trigger Pos. Amp. Display

CRT

Pre Xext Final Xinput Attenuator Amp. Amp. Horizontal X Channel int Pos.

Foc. Stab. 0 Freq. Ast. Command Σ Integrator u W F/F v ud uc ug ur Int. 0 −1 k Return Sweep F/F Manual Generator

Zinput

us +− Trigger Derivative F/F Circuit uq External Slope Trigger

Trigger Level

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

30 IEEE Instrumentation & Measurement Magazine December 2006 input channels. Generally the ADC is preceded by a sample- As before, the trigger circuit supports internal or external and-hold circuit that assures a constant voltage level at its triggering modes and includes a time base, a trigger com- output for each sample during analog-to-digital conversion parator, a delay counter, and a stop acquisition block. of that sample. Bandwidth specifications of these oscilloscopes working in In low-cost models, there is a single ADC shared by the real-time sampling mode are determined by the maxi- all input channels but the effective bandwidth of the mum signal sampling rate and associated Nyquist rate, con- oscilloscope depends on the number of active channels sidering that there are no additional bandwidth restrictions and the circuit must also include additional multiplexer caused by the input channel amplifier or compensation cir- and demultiplexer circuits, before and after the ADC. If cuits. For example, if the ADC has a maximum sampling rate there are multiple ADCs, it is possible to extend oscillo- of 100 MS/s and is dedicated to a single channel, the band- scope bandwidth below the Nyquist rate by using inter- width usually specified by the manufacturer is half the maxi- leaving techniques [11]–[13]. In this case, the mum sampling rate, which means for this example a analog-to-digital conversion of a single channel is per- 50-MHz bandwidth. However, this is a limit that only makes formed by multiples of ADCs, usually two, four, or sense for data processing applications, since the recovery of eight, and the samples are then ordered according to their temporal sequence. The unit controls all the functional blocks and performs multiple data processing tasks. There are two memory blocks. The acquisition memory, MemAcq , stores digitized samples during the acquisition cycle, and the display memory, MemDisp , stores a complete record of samples to be displayed. With the use of digital-to-analog converters (DACs), it is still possible to use CRTs as display units, but these oscilloscopes generally incorporate raster display units. The main advantages of using two different memory blocks are ◗ minimizing “blind acquisition periods,” which are times the oscilloscope doesn’t acquire the input signal ◗ enabling a screen update rate higher than the input sampling rate. Fig. 3. Didactic oscilloscope from Siemens.

Y1input Attenuator Vert. Amp. S and H ADC MemAcq

µ MemDisp P Raster Display

Y2input Attenuator Vert. Amp. S and H ADC MemAcq

Ext. Trig Trig. Delay Stop Time Attenuator Comp. Counter Acq. Base

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

December 2006 IEEE Instrumentation & Measurement Magazine 31 an analog signal is assured as long as the sampling rate is at Figure 5 represents the linear interpolation relative error least twice the maximum frequency value contained in the as a function of the number of samples per period for N = 4, signal bandwidth. However, for time and amplitude analy- 8, 16, 32, or 64. The relative error is evaluated using as refer- sis of sampled signals it is usual to consider a minimum of ence the peak-to-peak amplitude of a sinusoidal input signal 25 samples per signal period (N). However this limit and the time units are normalized to signal period. depends on the required amplitude accuracy and on the The interpolation error decreases with N and its maxi- interpolation method used for signal representation. mum value is lower than 1% for N = 16. By performing some additional calculations, it is possible to verify that the maxi- mum relative error for N = 25 is 102 N=4 about 0.39%. This means a value of almost 50 dB in terms of an associ- 101 ated signal-to-noise ratio. This is N=8 the signal-to-noise quantization

0 ratio of an ADC with 8 bits. So, this 10 N=16 N=32 means that the linear interpolation

error for N = 25 is almost equal to − 10 1 the quantization error of a typical 8-bit ADC in terms of maximum 10−2 error amplitude. Finally, to compare the errors Relative Error (%) for different interpolation meth- −3 = 10 N 64 ods, Figure 6 represents those errors for linear, cubic, and cubic 10−4 spline interpolation methods when the oversampling factor (N) is equal to 25. Previous results show 0 0.5 1 clearly that interpolation perfor- Time (n.u.) mance increases at the expense of the required computational load Fig. 5. Linear interpolation relative error as a function of the number of samples per period for N = 4, 8,16, 32, 64. of their implementation. If the sinc function (sin(πx)/πx) is used for interpolation, the results in this case are even better. However, the disadvantage of this Linear approach is that the results depend 0 10 on the assumption that the signal is band limited, but in practical terms, with a finite number of pulses it is Cubic 10−2 not possible to assure that condi- tion and the results obtained with spline interpolation are smoother and generally more accurate than −4 10 the results obtained with sinc func- tion interpolation.

Relative Error (%) The bandwidth of a DStO is − 10 6 Cubic dependent on the maximum sam- Spline pling rate of the ADC. However,

using equivalent time sampling techniques it is possible to capture −8 10 and display signals with frequen- cies much higher than the maxi- 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 mum sampling rate for the ADC Time (n.u.) [14], [15]. The hardware blocks of these oscilloscopes are very similar Fig. 6. Relative errors obtained with different interpolation techniques with an oversampling factor equal to 25. to the ones that are used in DStOs.

32 IEEE Instrumentation & Measurement Magazine December 2006 DSaOs Currently, the upper bandwidth limit is in the order of In a DSaO, an accurate sampling bridge is inserted before some tens of gigahertz, which means a timing accuracy and performing any signal attenuation or amplification, due to resolution better than a few picoseconds. However, it is sampling rate restrictions [16], [17]. The equivalent time important to note that this bandwidth is obtained at the sampling method can only be applied to repetitive wave- expense of a reduced dynamic range since there is no attenu- forms and not to single-shot events. Repetitive sampling ator/amplifier before the sampling bridge. The dynamic techniques capture data from multiple occurrences of the range of sampling oscilloscopes is usually limited to 1 V of input signal waveform. A set of points are acquired on each peak-to-peak amplitude. occurrence of the trigger event and after multiple trigger events the signal samples are ordered according to their time DPOs sequence. Since the data are not acquired in real time, in a The technology evolution that supported the appearing of single sweep, Nyquist criteria does not apply and the band- DPOs was the development of powerful microcontrollers, the width of sampling oscilloscopes is larger than the limit increment of integration scale in VLSI devices and the develop- imposed by ADC’s maximum sampling rate. ment of application specific integrated circuits (ASICs). DPOs Equivalent time sampling can be implemented in two display signals in three dimensions: time, amplitude, and different ways: sequential and random sampling. In amplitude over time. Each cell of the database screen that is sequential sampling mode, the capture delay after the trig- associated with a single pixel in the oscilloscope screen is rein- ger event is sequentially incremented after each acquisi- forced with intensity information each time the waveform tion cycle and a samples’ ordering algorithm is not image activates that cell. Doing so, the DPO translates probabil- required, since the sampling sequence preserves the sig- ity density function (PDF) data into displayed colors and inten- nal’s waveform time sequence. However, this sampling sities. These oscilloscopes include simultaneous advantages mode enables only post-trigger acquisitions since all the over analog and DStO enabling an extended number of auto- samples are taken after the trigger event. mated measurements capabilities: amplitude, time, area, phase, Figure 7 represents an illustration of the timing diagrams burst, histograms, and communication measurements. associated with the sequential equiva- lent time sampling technique. In this example, a single sample is taken 2 4 after a time delay that is incremented 2 3 4 3 1 with the occurrences of the successive Trigger trigger events. 1 In random equivalent time sam- 5 t Trigger pling, the sampling is done con- stantly, not waiting for a trigger t event. After the occurrence of multi- 5 ple acquisition cycles, the sampled points are ordered by measuring Fig. 7. Illustration of the timing diagrams associated with the sequential equivalent time sampling technique. the amount of time that elapsed between 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 25 (pretriggering) or before and after the trigger event (about trigger). Obviously, in this case, ordering the task is more 20 complex since the sampling sequence does not preserve the signal’s waveform time sequence. 15 The bandwidth specifications of these oscilloscopes are

mainly dependent on the accuracy and resolution of the (ps) t sampling timing circuits. Considering a minimum number ∆ 10 N=25 N=8 of samples per period equal to N, the required timing accu- N=16 racy must be lower than: 5 ≤ 1 t · N=32 N LB 0 510152025303540 where LB represents the oscilloscope bandwidth. LB (GHz) Figure 8 is a graphical representation of the previous rela- tionship for N = 8, 16, 25, and 32. The time units are in ps Fig. 8. Sampling timing requirements of DSaO as a function of bandwidth and the bandwidth units in gigahertz. and number of samples per period N = 8, 16, 25, 32.

December 2006 IEEE Instrumentation & Measurement Magazine 33 Vin Attenuator Vert. Amp. S and H Display

ADC Mem µ Mem Acq Proc.Acq Disp

µ Integrated Proc.Cont Acquisition/Display Unit µ Proc.Disp

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

The DPOs include unique ASIC components that Virtual Oscilloscopes acquire waveform images and explore parallel processing Currently, a substantial number of oscilloscopes are based architectures to increase the display updating rate. A sim- on PCs taking advantage of the potential of their hardware plified version of the vertical channel block diagram of a and software components. This approach is an acceptable DPO is represented in Figure 9. Relative to the DStO block solution for a large number of applications and PC diagram, the main differences appear after the ADC block. advanced signal processing modules can be used to obtain A DStO processes captured waveforms serially and even more measurement information than provided by stand- with very high-speed ADCs the speed of the microproces- alone oscilloscopes. sor unit limits the display update rate. The parallel archi- Data acquisition (DAQ) circuit boards are now available tecture of the DPO enables a direct copy of sampled data from many manufacturers and can be internally or externally from acquisition to display memory without delays. Signal connected to any desktop or computer. Graphical details, transient events, and other dynamic characteristics programming languages are generally used to develop dedi- of the signal are captured and displayed in real time with- cated software modules for data acquisition, processing, and out loss of information caused by “blind” acquisition peri- representation. These virtual oscilloscopes are cheaper and ods. The DPO for acquisition and display more flexible than the traditional versions, and such virtual work in parallel with the acquisition and display units, instruments are becoming popular in common applications respectively, without restricting acquisition process and that don’t require hard specifications. Advanced processing display update rate. tasks of measurement data can use a set of programs that are usually installed in every PC. Beside this advantage, the communication through local area networks (LANs) and the Internet is automatically assured by the communication ports of the PC, and data analysis, storage and transmission are easily implemented in a user friendly way. As an example, Figure 10 represents the front panel of a LabVIEW virtual instrument (VI), running a VISA applica- tion of a Tektronix oscilloscope that is connected to a PC through a GPIB channel [18], [19]. It is important to note that in this case the software modules developed in LabVIEW can access new functionalities that are not provided by the stand-alone oscilloscope. There are also some solutions of virtual oscilloscopes based on PC sound cards [20], [21]. The performances are Fig. 10. Virtual oscilloscope front panel developed in LabVIEW. obviously reduced but there is no additional price to pay as

34 IEEE Instrumentation & Measurement Magazine December 2006 long as the PC already includes a sound card. The main limi- [8] Iwatsu oscilloscopes [Online]. Available: tations of these virtual oscilloscopes are mainly associated http://www.iti.iwatsu.co.jp with low values of the input voltage dynamic range, input [9] Display technology: TFT-LCD technology [Online]. Available: impedance and bandwidth, typically lower than 20 kHz. An http://www.trl.ibm.com/projects/tftlcd/index_e.htm important note is that several oscilloscope simulators can be [10] WUEKRO training & didactic systems [Online]. Available: downloaded from the Internet that give some help in stu- http://www.english.wuekro.de/produkte_frame.asp dent activities [22], [23]. [11] Y.-C. Jenq, “Digital spectra of nonuniformly sampled signals: Robust sampling time offset estimation algorithm for ultra high- Conclusions speed waveform digitizers using interleaving,” IEEE Trans. This article gives an overview of the primary characteristics Instrum. Meas., vol. 39, pp. 71–75, Feb. 1990. and working principles of oscilloscopes. Starting from the [12] J.M. Dias Pereira, P.M.B. Silva Girão, and A.M. Cruz Serra, “An mechanical and light-beam oscillographs, the technological FFT-based method to evaluate and compensate gain and offset development associated with CRT devices and later with errors of interleaved ADC systems,” IEEE Trans. Instrum. Meas., semiconductor integrated circuits creates the basic infras- vol. 53, no. 2, pp. 423–430, Apr. 2004. tructure for analog oscilloscopes. The next step in the field of [13] J.M. Dias Pereira, A. Cruz Serra, and P. Silva Girão, “Dithering oscilloscope evolution is associated with digitalization and in interleaved ADC systems,” in Proc. IMEKO XV—World signal processing. Congress, Osaka, Japan, June 1999, vol. 4, pp. 81–84. Digital oscilloscopes store waveforms in digital format and [14] Tektronix, Application Note. Real-time versus equivalent-time present a large number of advantages that are inherent to sig- sampling [Online]. Available: http://www.tek.com nal digitalization. Some of these advantages are new measure- [15] J.M. Dias Pereira, A. Cruz Serra, and P. Silva Girão, “High ment capabilities provided by digital signal processing accuracy data acquisition of periodic signals,” in Proc. 9th Int. techniques, and the transmission capabilities supported by Symp. Elect. Instruments Industry, Glasgow, Scotland, Sept. 1997, different communication protocols. The continuous develop- vol. 1, pp. 141–144. ment in electronic technology, namely in VLSI devices, sam- [16] W.M. Grove, “A dc-to-2.4-GHz feed through sampler for pling bridges, microprocessors and raster display units, has oscilloscopes and other RF systems,” Hewlett-Packard J., vol. 18, increased the performance of oscilloscope devices. They made no. 2, pp. 12–15, Oct. 1966. it possible to capture very high frequency signals with DSaO [17] C. Gyles, “Repetitive waveform high frequency, high precision and using DPO to represent signals in three dimensions digitizer,” IEEE Trans. Instrum. Meas., vol. 38, no. 4, Aug. 1989. almost in real-time and without “blind” acquisition periods. [18] LabVIEW - The software that powers virtual instrumentation Even now with the advent of PCs and the development [Online]. Available: http://www.ni.com/labview of high-speed and high-resolution data acquisition boards, [19] National instruments VISA - products and services [Online]. together with dedicated software modules, it is possible to Available: http://www.ni.com/visa develop PC based oscilloscopes with increasing performance [20] Oscilloscope for the soundcard [Online]. Available: and new capabilities that can easily be integrated in a user http://www.zeitnitz.de/Christian/Scope/Scope_en.html friendly and flexible software application. [21] Virtins technology: turn a PC into virtual instrument [Online]. In the near future, the development of virtual instruments Available: http://www.virtins.com and the new capabilities provided by microprocessors, DSPs [22] Oscilloscope and spectrum analyzer products from Pico and other electronic devices will support the development of [Online]. Available:http://www.picotech.com new instruments with extended capabilities that will combine [23] Virtual oscilloscope: interactive simulation of an analogue 20 the specific functionalities of oscilloscopes, spectrum analyz- MHz oscilloscope [Online]. Available: http://www.virtual- ers and logic analyzers in a single instrument. oscilloscope.com

References J. Miguel Dias Pereira ([email protected]) received [1] Tektronix oscilloscopes [Online]. Available: http://www.tek.com degrees in electrical engineering from the Instituto [2] Agilent oscilloscopes [Online]. Available: Superior Técnico (IST) of the Technical University of http://www.home.agilent.com Lisbon (UTL) in 1982. During almost eight years he [3] Lecroy digital oscilloscopes [Online]. Available: worked for Portugal Telecom in digital switching and http://www.lecroy.com transmission systems. In 1992, he returned to teaching as [4] Chauvin-Arnoux, laboratory and educational instrumentation assistant professor in Escola Superior de Tecnologia of [Online]. Available: http://www.chauvin-arnoux.com Instituto Politécnico de Setúbal, where he is, at present, a [5] Kenwood TMI Corporation, oscilloscopes index [Online]. Available: http://www.kenwoodtmi.co.jp coordinator professor. In 1995 he received the M.Sc. degree [6] Instek oscilloscope selection guide [Online]. Available: and in 1999 the Ph.D. degree in electrical engineering and http://www.instek.com computer science from IST. His main research interests are [7] : oscilloscopes [Online]. Available: included in the instrumentation and measurements areas. http://www.hameg.com He is a Senior Member of the IEEE.

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