Electronic Design

Test & Measurement: Oscilloscopes

Oscilloscopes Ramp Up
When I was in high school, the physics teacher brought out the Dumont oscilloscope whenever it came time to discuss electricity. I don't recall its model number, and the demise of Dumont is ancient history. But with its formidable set of knobs clustered around the 5-in. CRT, it certainly appeared state-of-the-art to us tyros.

How far oscilloscope technology has come since then! CRT technology was the basic building block in oscilloscope innovation. It too has come far since its inception over a century ago. Driven by the need for radar in the '30s prior to World War II, CRT technology advanced to the point where it played a crucial role in the outcome of that war. Once peace returned in 1945, the CRT was ready to assume its place in the oscilloscope. It's still holding its own despite the onset of flat-panel displays.

Driven by demands for bandwidth and climbing data rates over the past half-century, the oscilloscope spawned digital scopes, sampling scopes, logic analyzers, and protocol analyzers. To do all of this, it has received major assistance from advances in silicon technology, the PC, and digital-signal processing.

Look for more specialized analysis packages. Because of the increasing complexity of system tests and time constraints, scopes are no longer primary measurement instruments. They are sophisticated analysis devices. A prime example is mask testing. Users will increasingly be able to program in added test procedures as new industry standards are approved. Also to be introduced are more specialized triggering packages, such as the serial pattern trigger just recently announced. It enables engineers to program a certain sequence of bits and trigger on that.

Probing is becoming more difficult, although help is on the way. The problem is primarily due to the continued shrinking of products and packaging, the advent of SMT packaging, and flip chips, which all make it increasingly difficult to place a probe on exactly the right node. Look soon for announcements of innovative probing techniques that will surmount these difficulties.

Engineers will probably always require a sampling oscilloscope as a lab instrument and as a reference point. But they like to work with real-time oscilloscopes. Clock rates in real-time scopes will continue climbing, driven in part by the climb in data rates, as will bandwidths, now in the vicinity of 4 GHz.

See associated timeline.

Jitter measurement is a hot topic right now, and it will become even more important. Oscilloscope performance in making jitter measurement depends heavily upon both the stability of its time base and the accuracy of the inputs. Not only will the performance of the oscilloscope be enhanced with regard to jitter, so will the ancillary jitter packages.

Logic and prototype analyzers are becoming a must for engineers in many sophisticated design situations, particularly in the telecommunications and wireless sectors. Consequently, T&M manufacturers will accelerate a trend already launched, which is to bring these additional capabilities to traditional oscilloscopes.

The mixed-signal capability of oscilloscopes will increase. The state-of-the-art in mixed-signal oscilloscopes is now two analog channels and 16 digital timing channels that enable timing-analyzer functionality. Expect to see the number of analog channels and digital-timing channels increase.

The demand for deep-memory oscilloscopes will become more widespread because of the need to capture longer intervals of time at a fast sample rate. Looking at it the other way around, with a given time window of interest, designers must capture signals at the maximum sample rate possible. Sample rates now are in the 1- to 8-Gsample/s range and will soon head higher.

Because it's essential to access the signals without disturbing the system, use of active probes will increase, not only in gigahertz-class oscilloscopes but also in 500-MHz oscilloscopes. By putting an amplifier out at the probe tip, loading is diminished, which means far less intrusive probing is realized.

As we become more familiar with the programs and tools of the PC, it's natural that oscilloscopes will either be bundled with PCs or will at least save data in compatible analysis programs that can be easily fed to a nearby PC. In many cases, users can already directly connect their oscilloscope to their PC, so transfers occur transparently.

Sampling rates are now in the neighborhood of 20 Gsamples/s on one channel. Coming soon will be higher sampling rates and multiple channels.

See associated timeline.

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