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Review: Agilent's InfiniiVision 4-Channel Oscilloscopes

The new Agilent InfiniiVision DSO/MSO 2000X and 3000X series oscilloscopes will certainly stir up the scope market. They combine high performance and a wide screen format with ease of use ? something that is not always a feature of today's digital scopes.

Review by Nicholas Vinen

The great thing about these new models is that they fill the gap between low-end, entry-level digital oscilloscopes and scopes with much higher performance, such as the Agilent 7000 series which have more daunting price tags.

There are 26 new Agilent InfiniiVision models ranging in price from about $1328 plus GST to over $12,000. The particular model we tested is somewhere in the middle.

And like high performance cars there are lots of options such as serial decoding modules (for the mixed signal oscilloscopes), a built-in signal generator, VGA and LAN connectivity, GPIB (General Purpose Interface Bus) and more.

First impressions

Turning now to the 200MHz MSO-X 2024A we tested, the immediately outstanding features are the large screen, a 21cm 800 x 480 LCD panel and the fast waveform update rate (50,000 acquisitions per second).

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Here's a view of the back of the scope. Of most interest is the right side, revealing two USB ports (device and host), trigger out and trigger in sockets and below them the optional LAN/VGA port, which well look at more closely shortly.

Not only is the screen large and crisp but it is immediately obvious that the analog front-end is well-designed. The waveforms look clean, even if you set it to maximum sensitivity (which with the provided 10:1 probes, is 20mV/division). At that level you can see a little noise from the acquisition circuitry but it is kept well under control.

This isn’t to say that the actual noise being measured has gone away – you can still see it but it is shown as a smooth band around the centre of the trace, thanks to the many sampled waveforms which are overlaid due to the rapid capture rate. The higher screen resolution contributes to the crispness of the displayed waveforms.

If signal noise is an issue, one of the excellent features of the InfiniiVision series (which we make use of regularly on our DSO7034A) is the “high resolution” acquisition mode. This uses oversampling to provide noise reduction similar to averaging mode but without introducing any delays or removing much high frequency information (aside from the noise, obviously). Waveform averaging is also supported, as is peak-detection mode.

The 2000X series oscilloscopes have a high sampling rate: 2GS/s (interleaved mode) or 1GS/s (non-interleaved). The advantage of non-interleaved mode is that each channel is sampled at exactly the same time but then the sampling rate is halved. The waveform memory is quite large at 100,000 points. The 3000X series has an even more impressive 2,000,000 points memory (with an option to double it).

What does the high acquisition rate mean for you, the user? You obviously can’t see 50,000 waveforms per second. Well it turns out that this is actually a very useful feature because the scope averages many sampled waveforms and uses the result to vary the intensity of each pixel. This is similar to what an analog scope with phosphor decay does.

In essence, if the waveform is not perfectly consistent, you can see the spread of voltage levels since some areas will be brighter than others. This makes it easier to see “glitches” (occasional deviations from the expected pattern) as well as giving you a better impression of just how much noise and jitter there is in the signal.

It’s not just a matter of trying to make the number more impressive – this is a true improvement in usability that was previously limited to very expensive DPOs (Digital Phosphor Oscilloscopes).

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Fig.1: using the test unit to make an amplifier distortion measurement, with the distortion residual at the top and the test waveforms underneath. Note the measurements at the right side of the screen with the orange dashed cursor indicating the peak-to-peak measurement points.
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Fig.2: the zoom mode is easy to operate, especially with the navigation buttons which perform constant-speed panning across the captured waveform. The large memory and low noise allow small details to be seen in the zoomed view. The scope updates at the full rate when in zoom mode.

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