Gameboy Oscilloscope （5）

Published:2011/8/2 1:43:00 Author:Amy From:SeekIC

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To start with, it is important to determine how much band­width and how many channels you need for the measure­ments you will be making - both now and in the future. After all, an oscilloscope’s bandwidth and number of channels cannot be upgraded later on. The next thing to consider is that an oscilloscope cannot be ’interfaced’ to the object to be measured without the proper probes and adapters. You are thus well advised to reserve a portion of your budget for such items.

It is also important to pay attention to the ’lifetime’ of the instrument, with regard to the availability of spare parts. The question of whether you should select an analogue scope or a digital scope depends on what it will be used for. Digital instruments suffer from noise, which can cause waveform details to be lost. However, a good digital instrument can have quite extensive memory and trigger­ing functions, while analogue instruments are clearly lim­ited in this regard.

If you decide on a digital storage oscilloscope, when determining the required sampling rate you should bear in mind that many of these instruments can measure in two different modes. The real-time mode is specifically intended to be used for making single-shot measurements up to the physical sampling rate limit of the A/D convert­ers. In the repetitive mode, a periodic signal can be sam­pled at a higher rate than what the A/D converters can actually handle. This involves making repeated real-time measurements at intervals that are successively offset by a small fraction of the period of the waveform. As the sig­nal is repetitive, the results of these measurements can be combined. As a result, it appears that the signal was sampled at a (much) higher sampling rate.

But note that this is strictly limited to repetitive signals. Some manufacturers are occasionally inclined to adver­tise this higher sampling rate, although the true physical rate is significantly lower.

You also have to pay attention to the memory depth. The larger the memory, the higher the sampling rate can be for a relatively long time interval (time base range). But a large memory is not always necessary, and sometimes it can even be undesirable, since processing an enormous amount of data generally slows down the operation of the oscilloscope.

You should also pay attention to the trigger options, and with digital oscilloscopes in particular, the functions that allow infrequent events (glitches) to be detected. Here the instrument’s performance also depends on the sampling rate and resolution in relatively large time intervals. Finally, you should also consider the (mathematical) analysis functions and report-generation features. Several basic functions are present with most of the manufactur­ers, and it is often possible to use supplementary soft­ware modules to expand the available features. Both the analysis software and the firmware of most digi­tal oscilloscopes are often subsequently upgraded, so it’s a good idea to keep track of these updates.

Incidentally, in the more expensive instruments all of the options are often already present, and they only have to be activated using the appropriate software keys. With digital oscilloscopes that run on a Windows platform, it is often possible to also run ’normal’ software, such as Mat-lab, on the same platform. This can also form a way to add extra functions.

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