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What's New In Oscilloscopes? Is it some time since you last looked at what's available in oscilloscopes? In this article, we'll update the oscilloscope scene, with special emphasis on CRT readout and the new digital storage models. By LEO SIMPSON In the last two years or so, For those not familiar the oscilloscope market has with CRT readout on changed radically. Convenscopes, we'll explain. Intional analog scopes are bestead of just having one, ing more and more overtwo or four· traces on the shadowed as digital storage screen, CRT readout scopes models become more powalso display the principal erful and also cheaper. At settings for the vertical senthe high end of the market, sitivity, timebase (sweep you can now obtain digital speeds), AC or DC input scopes with repetitive bandcoupling, probe settings widths up to 50GHz, a figand so on. The letters and ure undreamt of not so many numerals shown at the top CRT readout scopes can have simplified controls without years ago. and bottom of the scope a lot of labelling to clutter up the control panels since the But before we get carried screen are generated in exsettings are displayed on the screen. The Kikusui model COR5500 series are a very good example of this and have away with where the maractly the same way as are very clean and easy to use control panels. ket is heading, let's back up the alphanumeric characa little and see where it's ters on a computer screen. been. This is an interesting For quite a few years now, the basic will have even greater bandwidth, up contrast because while the scope oscilloscope has been an analog model to 150MHz or more, and perhaps four traces are generated by the method of with two channels, 20MHz band- instead of two channels. To provide "vector scan" whereby the CRT beam width, a maximum vertical sensitiv- the much faster trace writing speeds moves in direct response to the ity of 20mV/ division and a maximum required for these higher bandwidths, voltages applied to the vertical and sweep speed of 20 nanoseconds/divi- the oscilloscope tube will generally horizontal plates, the alphanumeric sion. Such an instrument can do a be a PDA (post deflection accelera- display is produced by a raster scan tion) type with a spiral anode running method (see the glos,sary accompanywide range of tests on audio and video equipment, logic circuitry including the full length. Inevitably, this adds to ing this article). computers and on some communica- the price. This means that the scope traces tions equipment. must spend some part of the time The next step up in features is to CRT readout scopes being "raster scanned" and the rest of Higher priced analog scopes now the time being "vector scanned". The have higher bandwidth, say 40MHz, and perhaps a delayed timebase which commonly have CRT readout, a feasharing of the trace between these enables you to more easily display ture introduced quite a few years ago two tasks is controlled by a micropulse waveforms with short duty cy- by the major manufacturers, Tektronix processor inside the scope and this cles and to be able to measure pulse and Hewlett-Packard. CRT readout is also takes care of the alphanumeric rise and fall times. a major innovation and also means a character generation. Higher priced analog instruments big increase in circuit complexity. Why have CRT readout on scopes? JUNE 1992 53 The overwhelming reason is to make them easier to use. Because scopes have so many knobs and buttons, with 20 or more settings in the case of the timebase controls, they can be very confusing to drive. In the middle of a complex measurement setup, particularly where delayed timebase settings are being used, it can be very easy to "get lost". The trace can "get lost" too and when this happens, it can take quite some to get your bearings and come to grips with the measurement. This is where CRT readout scopes excel. Because they display the principal settings on the Screen, you have a much better grasp of what the instrument is actually doing. You don't need to do anything special to display the measurement settings on the screen; it happens automatically. And each time you change a setting, say the timebase or vertical attenuator setting, the appropriate alphanumeric display changes automatically. And because all the settings are shown on the screen, the labelling of the front panel can be greatly simplified, which again makes the scope easier to drive. Apart from making a scope that This Kenwood CS-5170 100MHz CRT readout scope is displaying a standard PAL TV colour bar pattern, along with the channel 1 vertical attenuator setting of 0.5V/div and the timebase sweep speed of 20µs/div. much easier to use, the CRT readout has one big additio_n al benefit: if a photograph is taken of the screen, the measurement settings are also recorded. Screen photos In the past, the accepted method for recording screen information has been to take a photo with a specially designed Polaroid camera using fast film. As we shall see, digital storage scopes come with computer interfaces which allow screen and measurement data to be stored in computer memory for later retrieval. And some digital HITACHI COMPACT SERIES SCOPES CRT READOUT AND CURSOR SCOPES . V-1065A DC to 100MHz V-665A DC to 60MHz CRT READOUT SCOPES V-1060 DC to 100MHz V-660 DC to 60MHz Dual channel, delayed sweep, CRT readout , cursor readout (not provided on the V-1060 and V-660) , frequency counter (not provided on the V-1060 and V-660). sweep time autoranging, trigger lock. Hitachi Compact features CRT Readout, Sweep Time Autorang _ ing and Trigger Lock Functions. . . ST LUCIA ELE V212 AT $719 + TAX (V212 NOT SHOWN) AND "FLUKE" SCOPE METER'S FROM $1459 + TAX. ~ 54 SILICON CHIP HITACHI S . . 24 Campbell St. Bowen Hills Q 4006. Tel: (07) 252 7466 Fax (07) 252 2862 ECONOMIC ELECTRONICS: 22 Campbell St. Bowen Hills Q 4006. P.O. Box 481, Fortitude Valley 4006. Tel: /07) 252 3762. Fax /07) 252 5778. SOUTHPORT ELECTRONIC ~~if~tR°8 J:211£ Welch St. Tel: /075) 32 3632. Fax: /075) 51 0543. Electronics Workbench® The electronics lab in a computer! A simple, intuitive and very powerful teaching tool, Electronics Workbench lets students and hobbyists design and test both analog and digital electronic circuits, without the delays and expense of a laboratory • Yokogawa's DL1200 and DL1100 storage scopes have large memories for long waveform storage. They incorporate an optional printer but can also feed an external HP-GL printer or laser printer. FEATURES scopes, such as the Yokogawa DL-1200, come with an optional inbuilt printer, making a Polaroid scope camera unnecessary. LCD readout One manufacturer that has provided an alternative to CRT scopes has been Philips but they still recognise the need for displays of principal settings. Their method is to use a separate backlit liquid crystal display to show this information. It is probably even easier to read than CRT readout scopes but it cannot be recorded by means of a photo of the screen. We should note that most Philips digital storage scopes have CRT readout as a matter of course. • Quick and simple circuit entry • Digital and Analog Modules included, complete with all components • Simulated instruments: dual trace scope, spectrum analyser, function generator, multimeter, digital word generator and logic analyser • Complete control over all component values and parameters • Print: circuit schematics, parts list, instrument readings, macros • Logic conversion - truth table to Boolean formula to logic gates • Customisable hypertext help system THREE VERSIONS • Professional Version: EGA/VGA colour display; unlimited components • Personal Plus Version: Monochrome display; unlimited components • Personal Version: Monochrome display; limited to 20 components per .. EMONA INSTRUMENTS NSW ......................... (02) 519 3933 VIC ............................ (03) 889 0427 QLD .. .. ...................... (07) 397 7427 DISTRIBUTORS Perth .. ..... (09) 244 2777 Adela Ide .................. ...... (08) 362 7548 Hobart .. .... ... ...... .. ........ .. (002) 34 2233 EmonaLAB4 Four instruments in one package! Intelligent scopes On the even more upmarket scopes with CRT readout, the internal microprocessor is employed to do measure- The LAB4 has four full function test instruments: ■ DC POWER SUPPLY Triple output; 5V, 15V, 0-50V ·~ ~~p :i ■ DIGITAL MULTIMETER Full function, auto-ranging ■ FUNCTION GENERATOR 0.02Hz-2MHz, with SWEEP ■ FREQUENCY COUNTER 1Hz-100MHz input range Digital storage scopes can generate a lot of data and are most useful when they can be used to compare waveforms with previously stored signals. This Tektronix TDS640 (which has a sampling rate of 2 gigasamples/sec) is shown with the Tekemate TD100 which has a 50Mb hard disc and 1.44Mb floppy drive. All storage, recall and other functions are selected from menus on the scope screen. with neatly laid out and labelled front panel controls. Also, the LAB4 is compact and only takes up a small space, compared to four bench-top instruments. INDEPENDENT INSTRUMENTS Each instrument in the LAB4 is completely independent and can be switched ON or OFF as required. The LAB4 has only one 240V mains input, saving on multiple power points . Each instrument is clearly defi ned EMONA INSTRUMENTS NSW ......................... (02) 519 3933 VIC ............................ (03) 889 0427 QLD .......................... (07) 397 7427 DISTRIBUTORS Perth .. ... .. ... ... . .. .... ... (09) 244 2777 Adela ide ...... ... .. .... .. .. ... .. (08) 362 7548 Hobart ... . . ....... . .. . .... . (002) 34 2233 ]UNE 1992 55 --y ,_. ~ y~-,----=-...~--------,""""-., . . . EJ e1. ••! d. ,. .,.EJ -~· (::. . _b ., / .,~ ' This and other CRT readout scopes can also display time and date and other information which may be useful in later documentation. And finally, some of these "intelligent" analog scopes have digital outputs to enable screen signals to be sent to a printer or computer. Digital storage scopes Hewlett-Packard have been pioneers in the development of digital storage scopes and more latterly of raster scan models such as the 54601A 100MHz unit pictured here. HP has also just released the 54602A 4-channel model which has a bandwidth ofup to 250MHz. ments automatically. This adds little extra to the circuit complexity of the unit but greatly increases its use as an all-round measurement tool. For example, the Hitachi V-1150 150MHz CRT readout oscilloscope also incorporates a 150MHz frequency meter function and a wide bandwidth AC and DC voltage measurement func- tion which includes relative measurements in decibels. It will also measure and automatically display pulse rise and fall times, periods, overshoot, droop and so on. It also has moveable vertical cursors for time (period, rise time, etc) measurements and moveable horizontal cursors for voltage measurements. While analog scopes have been able to cope with most measurement situations, some types of signals have always presented a problem. How do you measure and display a waveform or signal which only occurs occasionally or is very fast? For example, all switch contacts bounce when they close and this leads to troublesome transient pulses. In the past, the way to display such single shot phenomena has been to use an oscilloscope tube with a special mesh structure behind the screen. The mesh was used to store the screen pattern so it could be displayed long enough for visual examination and to allow photos to be taken. Alternatively, some storage tubes had a secondary target and flood gun system to achieve much the same function. Patterns could be stored for about an hour. Some scopes have also had Glossary Alphanumeric characters: letters and numbers which may be displayed on the screen of a scope to show the principal settings being used. These are generated by an internal microprocessor in a similar way to that used on a computer monitor. Bandwidth: maximum frequency which can be displayed on the screen for a reduction in vertical deflection of 0.707 (ie, -3dB or half power point.) For example, a 20MHz signal displayed on a scope with a 20MHz bandwidth could be expected to display 70% of the amplitude of a signal at 1MHz. Beam: the electron beam from the cathode of an oscilloscope (CRT) tube. Usually the beam is split to give two or more traces, depending on the number of input channels. CRO: abbreviation for "cathode ray oscilloscope". This term is falling 56 SILICON CHIP into disuse and is being replaced by "scope". CRT: abbreviation for "cathode ray tube" which is the heart of any oscilloscope, TV or computer monitor picture tube, radar display, heart monitor and so on. A scope CRT has voltages applied to the vertical and horizontal plates which cause the electron beam to trace out a pattern on the electroluminescent screen. Quantising: process by which sampled signais are converted to digital data. Raster scan: method by which a display is produced on the screen of a TV set or computer monitor. The electron beam is scanned continuously and rapidly over the entire surface of the screen and then modulated to produce areas of light and shade in the case of a monochrome picture, or modulated on and off to the produce the dot ma- trix displays of computer monitors. Raster scan is also used on CRT readout scopes to produce alphanumeric displays. Sampling: process by which the signal levels of a waveform are taken by a digital to analog converter. These sampled signal levels are then "quantised" to convert them to digital data. For repetitive signals, the sampling rate must be at least twice the signal frequency. For non-repetitive signals, the sam-, pling rate must be at least 10 times the signal frequency in order to capture the waveform with reasonable fidelity. Vector scan: method by which voltages applied to the vertical and horizontal plates of an oscilloscope tube move the beam to trace out waveforms on the screen. Word: parcel of digital data or unit of memory in digital storage scope; usually eight bits. ~010000 Whether you speak 01010011 or analog, Philips provides you with a complete analog and digital oscilloscope in one instrument. With a sampling rate of 200 megasamples per second and a bandwidth up to 200 MHz our easy- to-use 4-channel oscilloscopes represent state-of-the-art technology. With direct access functions. Innovations like aprobe mounted button which allows you to recall set ups. Perform Autoset. Freeze display as well as display measured results. In the analog mode, extremely fast update and infinite display resolution allow you to see three dimensionally. For instance, the distribution of time-jitter. The digital mode is impressive. Logic triggering creates a true 4-channel logic analyzer. It is prepared for HDTV triggering. The powerful 0SO specifications_ give you extensive trace storage possibilities. And processing capabilities like FFT. At Philips, we're on your wavelength. Which is why we promise you one thing. You'll measure b~tter performance For further information please contact your local Philips Test & Measurement Organisation: SYDNEY (02) 888 0416 MELBOURNE (03) 881 3666 PERTH (09) 2TT 4199 WELLING.TON (04) 88 9788 BRISBANE (07) 844 0191 ADELAIDE (08) 348 2888 AUCKLAND (09) 89 4160 PHILIPS Tektronix was one of the pioneers of CRT readout scopes. Their model 2211 is a digital storage oscilloscope which uses a conventional CRT. variable persistence phosphors which enabled one-shot signals to be more easily examined. Such oscilloscope tubes were very expensive, had limited brightness and tended to bloom if you attempted to turn up the brightness. The tubes also did not last very long, especially if they were often used in storage mode. With the great expense of analog storage scopes, it was inevitable that logic circuitry and computer memory would eventually produce a digital storage oscilloscope. The first fully digital storage scopes by Hewlett Packard (HP54100) were introduced about 10 years ago. Since then, they have progressed gradually, with increasing bandwidth, sampling rate, memory and measurement functions. One of the new breed of LCD scopes, the Fluke Scopemeter combines a 50MHz digital storage scope and a 3000 count digital multimeter. 58 SILICON CHIP To date , most digital storage scopes have been a marriage of conventional analog scope technology with digital storage circuitry. These scopes can function as conventional analog instruments and are used in the digital storage mode only when necessary. Other digital storage scopes can only be used in digital mode. To display a signal on the screen, you set up the recording parameters, push a button and then the trace appears on the screen. They are powerful instruments but their very power makes them difficult to drive. All digital storage scopes have broadly the same internal circuit functions. First, they have attenuators for the input channels and the signal either passes to the vertical deflection amplifiers when in the analog mode or to the digital to analog conversion circuitry when in the storage mode. The signal is sampled, quantised and the digital data stored in memory. It can then be read out of memory, converted back to an analog signal and displayed on the screen. The beauty of having signals stored in memory is that, with suitable software, they can be stored indefinitely, for display at any time. Raster scan scopes In the past year or so though, the scene has changed quite radically with the introduction of digital scopes like the Hewlett-Packard 54600 series, the Yokogawa DL 1100/1200 series and similar machines from Tektronix, Le Croy and others. Two factors make these scopes different from earlier digital scopes. First, they do not use the expensive scope tube which is typically 40cm long or longer. Instead, they use a CRT which is just like that in a computer monitor and the display they generate is composed entirely of dots, not just the alphanumeric information. Because of this , they can display waveforms which move much more slowly or a great deal faster than possible on an analog scope and do it without having the trace becoming unusable. Second, this new generation of scopes can now respond to signal and measurement changes in such a way that they appear to behave exactly the same as analog scopes. Because of this, they are much easier to drive easier even than analog scopes. (To gain an insight into these new instru- like the feeling·of our new 1gital troubleshooting scope. Now there's a 100 MHz digital scope that handles just like analog. instantly to the slightest control change. Digital oscilloscopes have certain advantages that are hard to overlook. But for troubleshooting, many engineers still prefer analog scopes. Simply because they like the way they handle. But when it comes to troubleshooting, the HP 54600's digital performance leaves analog and hybrid scopes far behind. At millisecond sweep speeds, the display doesn't even flicker. Low-rep-rate signals are easy to see without a hood. The HP 54600 changes that. It looks like a 100 MHz analog scope. All primary functions are controlled directly with dedicated knobs. And itfeels like one. The display responds It has all the advantages that only a true digital scope can provide. Like storage, high accuracy, pretrigger viewing, hard copy output, and programming. And since it's one of HP's basic instruments the HP 54600 gives you all this performance at a very affordable price. So if you like the feel of analog control, you'll like the way our new digital scope handles troubleshooting. To find out more call the Customer Information Centre on 008 033 821 or Melbourne 272 2555. [hi] ~i~KLi~6 A Better Way. Just released: the HP 54602A scope with bandwidth up to 250MHz JWT HTM I 25/A - ~ .c"'"':::: OSOLI.DSCCPi .... oovoOOV►.1' 9 f !'0$:(fQI c:::, ~=~ 1,,00IC sco,-e 'ltw.'lCAl. Jo CH 1u1tll ~0 CH1"i/•llU5 l_ltY r ·='"'"'2::: .. 'lO'ol · - ~<( ► CH2 , r, Another of the new breed of LCD scopes, the Leader 300 is a dual channel storage unit with a sampling rate of 30 megasamples/sec & a bandwidth of 10MHz. It can record one-shot events with signals up to 3MHz. It can also function as a data logger, 8-channel logic scope and a digital multimeter. ments, refer to our review of the HP 54600 series in the October 1991 issue and the review of the Yokogawa DL1100 series in the April 1992 issue.) Interestingly, once the input signal is converted to digital data in these scopes, it is not converted back to an analog signal for subsequent display. Instead, the signal is converted in order to produce a dot matrix display, just as on a computer screen. Because the signal display is en- tirely made up of dots, there are no problems with the trace becoming faint when displaying very high frequency signals or becoming just a very bright dot when displaying very low frequency signals. In just about all measurement situations, the raster scanned scope can produce a display which gives as much, if not more, information and it will generally present less problems in producing a steady display. And even if the signal is rapidly changing, the display can The Le Croy 7200 series digital scopes have a bandwidth of 500MHz and a sampling rate of 2 gigasamples/sec. They are equipped with an internal hard disc for data logging and a floppy drive for waveform storage. 60 SILICON CHIP be frozen to enable you to examine it at leisure. Having said that, there will be times when the display from an analog signal is significantly different to that produced on a digital scope, for the same signal. This does not necessarily come down to a matter of one scope being right and the other one being wrong. It is more a matter of correct interpretation. Over many years, technicians and engineers have become expert at interpreting the displays on analog scopes. In some cases, they will have to learn how to interpret the displays again when they see the signals on a digital scope. Just about all digital scopes are available with interfaces which enable them to be hooked up to computers or printers. Two interfaces aie the most common: RS-232 and IEE-488 or GP-IB (HP's General Purpose Instrument Bus). With appropriate software, not only can data be collected via the scope but its operating parameters can be changed under program control. LCD scopes Finally then, there is the new generation of LCD scopes, as typified by the Fluke PM97 Scopemeter. This uses a green backlit LCD screen and can display signals up to 50MHz. It combines a 3000 count digital multimeter, making it a potent tool for work in the field away from mains power. And which one is ideal for you? Your budget is the first consideration as scopes today range in price from just under $500 to $50,000 or more. For most applications, the analog scope functions very well but it is being gradually supplanted by the digital scope. And while today, the analog scope has the bulk of sales, in five years time or less, digital scopes can be expected to have the major part of the market. They are dropping in price and improving in performance. In just about all test applications, you can find a storage scope which will do the job as well as, if not better, than an analog scope. And its ability to be programmed, to recall waveforms and to produce a rock-steady display is rapidly putting the analog scope in the shade. Where the analog scope will continue to hol.d its own is where waveforms need to be displayed with utmost accuracy and where noise must not be hidden in jitter. SC