Gameboy Oscilloscope （4）

Published:2011/8/2 1:19:00 Author:Amy From:SeekIC

Digital storage oscilloscopes

The Wittig 22-300, the simplest instrument in the ’pure digital’ category, is limited with regard to more than just its bandwidth and sampling rate. Its operation, measure­ment capabilities and display fall short of qualifying it for serious use. This is offset by its modest price. However, you would be wise to consider purchasing a good ana­logue instrument for the same money. If you specifically need storage capability, it’s worth giving thought to sav­ing up for an instrument with greater capability.

The same feeling prevails with the Voltcraft 6150, although it has significantly more extensive features. It has a variety of measurement functions, including spec­tral analysis using fast Fourier transform (FFT), that can be used via a clear, well-organized menu. Nevertheless, we could not obtain a good display of the test signal, but as already noted, that can’t be expected from an instru­ment with such a limited sampling rate.

The next instrument, the LDS Sigma 60-4, is some­what unique. Although the sampling rate of this instru­ment is 200 MSa/s, which cannot be considered to especially high, it does have several unusually useful features. The Sigma is particularly suitable for long-term signal analysis. This is demonstrated by features such as hard-disk recording, extensive triggering options, analy­sis functions and report-generation options. This is also the first instrument in this test that is built on a PC plat­form. ’Standard’ MS Windows is used as the operating system, so data from the measurement programs can be easily transferred to other programs (including user-writ­ten programs).

Despite the fact that the acquisition software runs under Windows, a non-standard menu structure has been cho­sen. We don’t consider this to be a logical choice, since it costs significant extra effort to become adept at oper­ating the scope. This is further complicated by the fact that only a few real knobs are present for changing set­tings. These knobs are constantly assigned different func­tions, depending on the menu selected using the touch screen (or the keyboard and mouse). We don’t consider this convenient.

The Tektronix 2024 is the first digital scope in this test with a serious sampling rate — no less that two gigasamples per second. This is where the concept ’digital’ starts to become attractive. All of its functions — triggering, measurement options, etc. — are just right. This full-grown digital scope is also packaged in an especially small housing. However, you should bear in mind that with regard to screen resolution, this instrument is far from being the equal of a good analogue scope.

Next we have the Yokogawa DL1740EL. This scope is also packaged in an unusual enclosure with an attrac­tive colour screen. In addition, the sample we received was equipped with a built-in thermal printer. Like the Sigma 60-4, this instrument is based on a PC platform and has its own operating system. Although some of the knobs are also assigned different functions depending on the menu selection, it has dedicated knobs for the basic settings (unlike the Sigma scope). It is thus possible to quickly learn how to use the instrument, despite its exten­sive features.

This instrument is also distinguished by extensive trigger­ing options. For instance, it can be triggered on a spe­cific l2C pattern, which allows the values of the bits to be viewed directly. Triggering on the test signal did not pre­sent any problems. With regard to technical aspects, this instrument is perfectly in order.

Actually, that’s true of all of the brands at this level and above — the technical aspects are not the issue. The most significant differences among the various instru­ments lie in their housing, operation, features and display quality, among other things.

The Agilent 54642D has remarkably good display quality for a digital scope, despite the fact that it uses a relatively small monochrome screen. However, the on­screen menu could hove been made a bit smaller; we found it rather obtrusive. In contrast to the -A version of this Agilent model, the -D version has a full sixteen digital inputs in addition to two analogue inputs. Besides stan­dard triggering, this scope can also work with l2C, SPI, CAN, LIN and USB signals.

The final member of this group is the LeCroy Wavesurfer 424. We are enthusiastic about this instru­ment, although it also has its own peculiarities. For instance, the automatic calibration feature often ’gets in the way’, although the frequency of automatic calibration does decrease after the instrument reaches its operating temperature. In addition, it can be switched off for mea­surements where accuracy is not important. We were pleased that v/e could quickly figure out how to do this, without using the manual. That’s probably in part due to the fact that a ’Windows-like’ user interface was chosen for this instrument. As a result, using the Wavesurfer is generally reasonably intuitive. The display is excellent and generously sized. Using the extra functions, such as zoom­ing in on a portion of the signal, is thus a real pleasure. The instrument could handle our test signal without any problems, although when we experimented with the mathematical functions we noticed that everything slowed down. That’s hardly surprising when you consider how much data has to be processed every second.

Ultimately, all of the instruments in this group suffer more or less from this problem. If you’re considering purchas­ing an oscilloscope in this price class, we recommend making comparative tests of several different instruments using your own specific measurement setups. This advice is certainly applicable to the final three instru­ments in this test: the Agilent Infiniium 54843A, LeCroy Wavepro 7100 and Tektronix TDS7154B.

Although even more expensive oscilloscopes are avail­able, for this test we considered them to be the top end of the normal market. For this reason, we gave more attention to them than to the rest of the selection. The results are presented in a separate inset.

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