IEEE Instrumentation & Measurement Magazine
The History and Technology of Oscilloscopes
An overview of its primary characteristics and working principles
O
scilloscopes are one of the main tools for analyz- ing electrical signals. The primary information obtained from the waveform of the signal is visualization of its amplitude variation over time. Oscilloscopes are excellent tools for testing, debug- ging, and troubleshooting because they can easily detect waveforms and demonstrate if the elec-trical components or circuit modules are working properly. Oscilloscopes also provide support during the design
of new electronic circuits. In addition to electrical signals, other physical or chemical quantities can be measured by using different probes that have been developed into an appropriate 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 the main characteristics of the different types of oscilloscopes and correlate their evolution with the development of the underlying technologies they incorporate.
Introduction
André-Eugène Blondel was a French physicist who was born on 28 August 1863. He is known as the inventor of the electromagnetic oscillograph, a device that enabled the observation of alter- nating signals. The first oscillographs traced an ink record on 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
on a set of mechanical devices, the first oscillographs had a very low bandwidth in the range of 10–19 Hz.
The first evolution of these instruments came with the development of light-beam oscillographs. In these instru- ments, there was still a moving coil but this coil was attached to a mirror and a light beam was reflected onto a moving photographic film. With these instruments, the mechanical bandwidth restrictions were a little bit reduced and the band- width increased to 500 Hz.
Some years later, in 1897, Karl Ferdinand Braun invented the cathode ray tube (CRT). The British company A.C.
Cossor (later acquired by Raytheon) designed the first dual beam oscilloscope in the late 1930s. It applied an oscillating reference signal to horizontal deflector plates and the input measured signal to the vertical deflector plates. Images of transient electrical signals were then obtained on a small phosphor screen.
In 1946, Howard C. Vollum and Jack Murdock invented the triggered oscilloscope that synchronizes the graphical representation of repetitive signal waveforms. Since then, and especially after the Tektronix [1] foundation, the majority of oscilloscope manufacturers [2]–[8] have technically improved their products. Bandwidth and accuracy have con- tinuously increased, first with analog oscilloscopes and later with digital sampling oscilloscopes that enable measurement of bandwidths in the range of tens of gigahertz.
Oscilloscopes became an essential instrument to support technological development in all engineering areas. Digital technology associated with digital phosphor oscilloscopes enables the measurement of statistical data (e.g., jitter) that were unavailable some years ago. Now oscilloscopes enable many more functions than a simple representation of time varying signals; digital signal processing techniques are adding new functionalities of spectrum and logic analyzers to modern oscilloscopes.
A few words must also be dedicated to the role of oscillo- scopes in teaching activities. It is difficult to find a more complete instrument for didactic purposes. Analog and digi- tal versions of oscilloscopes are by themselves a complete study case for several electrical engineering subjects includ- ing signal conditioning, analog-to-digital conversion, analog signal processing, digital signal processing, and communica- tion protocols (e.g., RS232, USB, GPIB and Ethernet).
Modern oscilloscopes can also be connected to a network for printing, file sharing, Internet access, and advanced commu- nication functions like sending e-mails triggered by pro- grammed events.
Oscilloscope Functional Blocks
To simplify the description, I have chosen to explain a classical analog 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 the correct amplitude of the signals that are delivered to the hor- izontal deflector plates of the CRT.
The horizontal channel generates a signal that is applied to the vertical deflector plates of the CRT. This signal has a saw-toothed waveform when the instrument is to provide the temporal representation of the acquired input signal (Y) or it has an arbitrary waveform from the external input (X), when the oscilloscope is used in the X-Y representation mode.
The oscilloscope time basis unit contains the circuits that generate the saw-toothed waveform, which provide the hori- zontal sweep of the CRT electronic beam. The time basis also provides a blanking pulse to extinguish the electronic beam between 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 the display, would be visible by the user.
The trigger unit contains a set of circuits that generates the timing signals to synchronize the start of sweep with timing pulses generated from the input signal (internal trigger) or from an external signal (external trigger). This triggering function is essential to achieve a stable image in the display unit. Without triggering, multiple copies of the waveform are drawn in different places on the dis- play, giving an incoherent jumble or a moving image on the screen.
As an example, Figure 1 represents a periodic input sig- nal (y), the sweep signal (sw), and the waveform displayed in the CRT unit. The trigger threshold has zero amplitude and a positive edge-trigger set-up and the hold-off time is equal to the signal period (T). The sweep signal has a period three times the input signal period (TH= 3T) and the sweep speed is equal to T/5 s/div, assuming a display unit with the typical ten divisions in the horizontal time axis.
The synchronization between input and sweep signals, implemented by the trigger circuits, is essential to obtain a stable image on the screen, which means multiple sweeps with the same waveform. The synchronization is still obtained 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 where the waveforms become visible due to the impact of the elec- tronic beam on a fluorescent and phosphorescent coating material. Currently, the CRT display units are being
replaced by the thin film transistor liquid crystal display (TFT LCD) [9]. These displays can achieve high brightness at low drive voltages and current densities, which result in more compact units with a lower power consumption.
Oscilloscope Types
Oscilloscopes can be either analog or digital. There are still a large number of analog oscilloscopes in use, but they are being gradually replaced by digital oscilloscopes. Much like PCs, the cost of digital oscilloscopes is dropping, and they are using the latest, low-cost, electronic developments in components. Equivalent time-sampling techniques are used in the sampling oscilloscope to extend the bandwidth when- ever repetitive and stable high frequency signals are mea- sured. Digital phosphor oscilloscopes enable the representation of an electrical signal in three dimensions, time, amplitude, and amplitude over time, using an almost real-time screen update rate. Virtual oscilloscopes based on data acquisition boards or sound cards are also an attractive solution for a large number of applications since they use the hardware and software already available in PCs.
Analog Oscilloscopes
The main hardware blocks of an analog oscilloscope include one or multiple vertical channels, the horizontal channel, the time basis, the trigger circuit, and the CRT unit where sig- nals’ waveforms are displayed. The vertical channel includes a compensated attenuator, a preamplifier, a delay circuit, and a final vertical amplifier that boost the input signal to a level 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 output signal to a level adequate for the horizontal sensitivity of the CRT unit. If working in internal mode, the input signal is a 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- 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 the saw-toothed signal used by the horizontal channel when it is working in internal operating mode. It is important to note that the start of the ramp contained in a saw-toothed signal is triggered by internal or external events, but when the ramp signal reaches its maximum amplitude, that corresponds to 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- 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 that outputs a rectangular waveform synchronized with trig- ger events. Control of trigger level is provided by varying the transition voltages of the Schmitt trigger. And finally, the
output trigger pulse that must define the start of sweeps accurately is obtained from the output of a derivative circuit.
The CRT is a special kind of vacuum tube that contains an electron gun, a set of vertical and horizontal deflector plates (mentioned previously), several electronic lenses, anodes, and a display internally coated with a fluorescent and phosphorescent coating material. Figure 2 represents a simplified version of the hardware block diagram of an ana- log oscilloscope.
Figure 3 is an old model of a didactic oscilloscope from Siemens [10] that has its electrical schematic diagram displayed on the front panel. This laboratory oscilloscope provides easy access to multiple internal signals. It is possible to simultane- ously display the external input signal and multiple test-point signals of the main internal circuits of the oscilloscope.
Typically the bandwidth of an analog oscilloscopes is in the hundreds of megahertz and the main limitation is the CRT dis- play unit. These devices can be used to display rapidly varying signals in real time since there is no digitalization, memory buffering, or any kind of signal processing between the input signal and the output display unit. The acquired signal is dis- played continuously with only negligible delays that are caused by the hardware components of the electrical circuits.
Digital Oscilloscopes
It is typical to divide digital oscilloscope into three main categories:
◗ digital storage oscilloscope (DStO) that uses real-time sampling techniques
◗ digital sampling oscilloscope (DSaO) that uses equiva- lent time sampling techniques
◗ digital phosphor oscilloscope (DPO) that uses advanced signal 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) waveform displayed in the CRT unit.
t y
0 T 2T 3T
TH t
Display Unit
sw Trigger
Hold Off
(a)
(b)
DSOs
DSOs became possible with the technological evolution of hybrid analog-to-digital converters (ADCs) that were fast and accurate enough to digitize high-frequency signals, the development of memories that could store input data as fast as 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 those values 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 them permanently, without need of special persistence tubes or photographic set-ups
◗ the advantage of digital data storage, in magnetic peripheral units, for future analysis
◗ the capability to implement data processing algorithms to access additional measurement information, for example, the signal spectrum by using fast Fourier transform (FFT) algorithms
◗ the improvement of signal transmission capabilities provided by the digital I/O communication ports (RS232, USB, GPIB, and Ethernet between others).
The functional blocks of these oscilloscopes include a compensated attenuator and a vertical amplifier that trans- lates the input signal range to a voltage interval that must be included in the ADC’s input voltage range. A simplified functional 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.
Pre Amp.
Final Delay Amp.
Vertical Channel
Display
Pre Amp.
Final Xinput Amp.
Yinput
Horizontal Channel
CRT
Foc.
Ast.
Int.
Zinput Pos.
Xext
Sweep
Generator Manual
−1 Stab.
Return F/F
Integrator Command
F/F W
k
Trigger
Trigger F/F
Derivative Circuit
Level External
Trigger
Trigger Pos. Amp.
Xint
0 Freq.
0
uv ug
us
uq uc
ur ud
Slope Attenuator
Σ
+−
Attenuator
input channels. Generally the ADC is preceded by a sample- and-hold circuit that assures a constant voltage level at its output for each sample during analog-to-digital conversion of that sample.
In low-cost models, there is a single ADC shared by all input channels but the effective bandwidth of the oscilloscope depends on the number of active channels and the circuit must also include additional multiplexer and demultiplexer circuits, before and after the ADC. If there are multiple ADCs, it is possible to extend oscillo- scope bandwidth below the Nyquist rate by using inter- l e a v i n g t e c h n i q u e s [ 1 1 ] – [ 1 3 ] . I n t h i s c a s e , t h e analog-to-digital conversion of a single channel is per- formed by multiples of ADCs, usually two, four, or eight, and the samples are then ordered according to their temporal sequence.
The microprocessor 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.
As before, the trigger circuit supports internal or external triggering modes and includes a time base, a trigger com- parator, a delay counter, and a stop acquisition block.
Bandwidth specifications of these oscilloscopes working in the 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 restrictions caused by the input channel amplifier or compensation cir- cuits. For example, if the ADC has a maximum sampling rate of 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 a 50-MHz bandwidth. However, this is a limit that only makes sense 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
Attenuator Trig.
Comp.
Delay Counter
Stop Acq.
Time Base MemAcq MemDisp
an analog signal is assured as long as the sampling rate is at least twice the maximum frequency value contained in the signal bandwidth. However, for time and amplitude analy- sis of sampled signals it is usual to consider a minimum of 25 samples per signal period (N). However this limit depends on the required amplitude accuracy and on the interpolation method used for signal representation.
Figure 5 represents the linear interpolation relative error as 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 signal and 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 is possible to verify that the maxi- mum relative error for N= 25 is about 0.39%. This means a value of almost 50 dB in terms of an associ- ated signal-to-noise ratio. This is the signal-to-noise quantization ratio of an ADC with 8 bits. So, this means that the linear interpolation error for N= 25 is almost equal to the quantization error of a typical 8-bit ADC in terms of maximum error amplitude.
Finally, to compare the errors for different interpolation meth- ods, Figure 6 represents those errors for linear, cubic, and cubic spline interpolation methods when the oversampling factor (N) is equal to 25. Previous results show clearly that interpolation perfor- mance increases at the expense of the required computational load 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 approach is that the results depend on the assumption that the signal is band limited, but in practical terms, with a finite number of pulses it is not possible to assure that condi- tion and the results obtained with spline interpolation are smoother and generally more accurate than the results obtained with sinc func- tion interpolation.
The bandwidth of a DStO is dependent on the maximum sam- pling rate of the ADC. However, using equivalent time sampling techniques it is possible to capture and display signals with frequen- cies much higher than the maxi- mum sampling rate for the ADC [14], [15]. The hardware blocks of these oscilloscopes are very similar to 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.)
Relative Error (%)
Linear
Cubic Spline
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.)
Relative Error (%)
N=4
N=64 N=16
N=8 N=32
DSaOs
In a DSaO, an accurate sampling bridge is inserted before performing any signal attenuation or amplification, due to sampling rate restrictions [16], [17]. The equivalent time sampling method can only be applied to repetitive wave- forms and not to single-shot events. Repetitive sampling techniques capture data from multiple occurrences of the input signal waveform. A set of points are acquired on each occurrence of the trigger event and after multiple trigger events the signal samples are ordered according to their time sequence. Since the data are not acquired in real time, in a single sweep, Nyquist criteria does not apply and the band- width of sampling oscilloscopes is larger than the limit imposed by ADC’s maximum sampling rate.
Equivalent time sampling can be implemented in two different ways: sequential and random sampling. In sequential sampling mode, the capture delay after the trig- ger event is sequentially incremented after each acquisi- tion cycle and a samples’ ordering algorithm is not required, since the sampling sequence preserves the sig- nal’s waveform time sequence. However, this sampling mode enables only post-trigger acquisitions since all the samples are taken after the trigger event.
Figure 7 represents an illustration of the timing diagrams associated with the sequential equiva-
lent time sampling technique. In this example, a single sample is taken after a time delay that is incremented with the occurrences of the successive trigger events.
In random equivalent time sam- pling, the sampling is done con- stantly, not waiting for a trigger event. After the occurrence of multi- ple acquisition cycles, the sampled points are ordered by measuring 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 (pretriggering) or before and after the trigger event (about trigger). Obviously, in this case, ordering the task is more complex since the sampling sequence does not preserve the signal’s waveform time sequence.
The bandwidth specifications of these oscilloscopes are mainly dependent on the accuracy and resolution of the sampling timing circuits. Considering a minimum number of samples per period equal to N, the required timing accu- racy must be lower than:
t ≤ 1 N· 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 ps and the bandwidth units in gigahertz.
Currently, the upper bandwidth limit is in the order of some tens of gigahertz, which means a timing accuracy and resolution better than a few picoseconds. However, it is important to note that this bandwidth is obtained at the expense of a reduced dynamic range since there is no attenu- ator/amplifier before the sampling bridge. The dynamic range of sampling oscilloscopes is usually limited to 1 V of peak-to-peak amplitude.
DPOs
The technology evolution that supported the appearing of DPOs was the development of powerful microcontrollers, the increment of integration scale in VLSI devices and the develop- ment of application specific integrated circuits (ASICs). DPOs display signals in three dimensions: time, amplitude, and amplitude over time. Each cell of the database screen that is associated with a single pixel in the oscilloscope screen is rein- forced with intensity information each time the waveform image activates that cell. Doing so, the DPO translates probabil- ity density function (PDF) data into displayed colors and inten- sities. These oscilloscopes include simultaneous advantages over 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.
Trigger t
1
2 3 4
5
1
2 4
t 5
3 Trigger
Fig. 8.Sampling timing requirements of DSaO as a function of bandwidth and number of samples per period N = 8, 16, 25, 32.
5 10 15 20 25 30 35 40
0 5 10 15 20 25
∆t (ps)
LB (GHz) N=8 N=25 N=16
N=32
The DPOs include unique ASIC components that acquire waveform images and explore parallel processing architectures to increase the display updating rate. A sim- plified version of the vertical channel block diagram of a DPO is represented in Figure 9. Relative to the DStO block diagram, the main differences appear after the ADC block.
A DStO processes captured waveforms serially and even with 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 data from acquisition to display memory without delays. Signal details, transient events, and other dynamic characteristics of 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 display work in parallel with the acquisition and display units, respectively, without restricting acquisition process and display update rate.
Virtual Oscilloscopes
Currently, a substantial number of oscilloscopes are based on PCs taking advantage of the potential of their hardware and software components. This approach is an acceptable solution for a large number of applications and PC advanced signal processing modules can be used to obtain more measurement information than provided by stand- alone oscilloscopes.
Data acquisition (DAQ) circuit boards are now available from many manufacturers and can be internally or externally connected to any desktop or laptop computer. Graphical programming languages are generally used to develop dedi- cated software modules for data acquisition, processing, and representation. These virtual oscilloscopes are cheaper and more flexible than the traditional versions, and such virtual instruments are becoming popular in common applications that don’t require hard specifications. Advanced processing 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 obviously reduced but there is no additional price to pay as Fig. 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.Cont
Integrated Acquisition/Display
Unit
Attenuator Vert. Amp. S and H
ADC
long as the PC already includes a sound card. The main limi- tations of these virtual oscilloscopes are mainly associated with low values of the input voltage dynamic range, input impedance and bandwidth, typically lower than 20 kHz. An important note is that several oscilloscope simulators can be downloaded from the Internet that give some help in stu- dent activities [22], [23].
Conclusions
This article gives an overview of the primary characteristics and working principles of oscilloscopes. Starting from the mechanical and light-beam oscillographs, the technological development associated with CRT devices and later with semiconductor integrated circuits creates the basic infras- tructure for analog oscilloscopes. The next step in the field of oscilloscope evolution is associated with digitalization and signal processing.
Digital oscilloscopes store waveforms in digital format and present 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 processing techniques, and the transmission capabilities supported by different communication protocols. The continuous develop- ment in electronic technology, namely in VLSI devices, sam- pling bridges, microprocessors and raster display units, has increased the performance of oscilloscope devices. They made it possible to capture very high frequency signals with DSaO and using DPO to represent signals in three dimensions almost in real-time and without “blind” acquisition periods.
Even now with the advent of PCs and the development of high-speed and high-resolution data acquisition boards, together with dedicated software modules, it is possible to develop PC based oscilloscopes with increasing performance and new capabilities that can easily be integrated in a user friendly and flexible software application.
In the near future, the development of virtual instruments and the new capabilities provided by microprocessors, DSPs and other electronic devices will support the development of new instruments with extended capabilities that will combine the specific functionalities of oscilloscopes, spectrum analyz- ers and logic analyzers in a single instrument.
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J. Miguel Dias Pereira (joseper@est.ips.pt) received degrees in electrical engineering from the Instituto Superior Técnico (IST) of the Technical University of Lisbon (UTL) in 1982. During almost eight years he worked for Portugal Telecom in digital switching and transmission systems. In 1992, he returned to teaching as assistant professor in Escola Superior de Tecnologia of Instituto Politécnico de Setúbal, where he is, at present, a coordinator professor. In 1995 he received the M.Sc. degree and in 1999 the Ph.D. degree in electrical engineering and computer science from IST. His main research interests are included in the instrumentation and measurements areas.
He is a Senior Member of the IEEE.
