Like a fine bouillabaisse, instruments are being blended with software, and what's emerging from the caldron is both evolutionary and revolutionary. The evolution is, as we would expect, driven by the continuing upward spiral of frequency and data rate. But the revolutionary capability stems from a most novel innovation in which signals and their software emulation become virtually interchangeable. This leads to an unusually powerful feature for those engaged in electronic design automation (EDA).
What's so astonishing about this event is how ingredients, both real and virtual (signals and software emulation), have been combined quite seamlessly to assist all who develop products to complete their designs more rapidly than ever. At the relatively humble beginnings of the oscilloscope and the logic analyzer, there was barely a hint of the powerful capabilities today's instruments provide routinely.
Though the oscilloscope predates World War II, it didn't begin to move into an aggressive development phase until the 1950s. One of the pioneers in oscilloscopes is Walter LeCroy Jr., the founder of LeCroy Corp. (see "Oscilloscopes: From Simply Viewing To Complex Signal Analysis," p. 76).
Another person who has both witnessed and participated in the oscilloscope's evolution is Ed Caryl, an oscilloscope applications engineer at Tektronix. He has been active in scope design for over 30 years. "There has been a four-order-of-magnitude progression over the past half century, with bandwidths at 5 MHz in the '50s climbing to over 50 GHz at present," he says.
"Back in the '50s, a user was lucky to get an oscilloscope to edge trigger," Caryl continues. Now, scope users can choose from a cafeteria of trigger sources, from very narrow pulses to very complex descriptions of parallel- and serial-bit streams. But according to Caryl, even these steps forward were wild dreams just a few years ago.
As the years passed, the kinds of measurements that oscilloscope users could perform on signals grew much more complex. Just 10 years ago, oscilloscopes were mostly analog in nature, only displaying a waveform. There was very little computation in the general-purpose oscilloscope, other than basic measurements.
Now oscilloscopes are actual PCs that do many complex computations on their own. Today, with the dramatic connectivity improvements to PCs, both internal and external, one can feed waveforms into multiple applications, such as Java and Windows. This has vastly expanded the designer's ability to analyze waveforms.
As for digital scopes, 10 years ago record lengths were 1000 to 2000 samples. Now 20 to 30 Msamples are commonplace. Also, 10 years ago the typical bench scope provided a bandwidth in the 400- to 500-MHz region.
"Of course, there were scan converters up to 5 GHz, but there was no vertical amplifier. You simply directly connected the scan converter tube or a CRT, with no attenuators, no amplifiers, and no ability to modify the signal. You scanned the signal, digitized it, and thus captured it in some crude form," says Caryl. Now real-time scopes offer designers 6-GHz bandwidths with 100,000-point record lengths, plus the ability to respond to complex triggering and perform sophisticated analysis.
Will sampling and real-time scopes merge in the next 10 years? Caryl thinks that's not very likely. The gap is wide: 6 GHz for real-time scopes and 55 GHz for sampling versions. It will be very hard to reach the higher levels in real time due to the front-end circuitry in a real-time scope. The attenuators and amplifiers limit the bandwidth before you get to the analog-to-digital converter. In a sampling scope, these circuits aren't an issue because the sampling bridge captures the signal. It's right out in front, immediately behind the 50-W connector.
The logic analyzer, on the other hand, began in the early 1970s. One of its pioneers was Chuck Small of Agilent Technologies, then Hewlett-Packard (see "How Microprocessor Systems Defined The Logic Analyzer," right). Another major innovator of the logic analyzer is Chuck House (see Logic Analyzers, Then And Now," p. 80).
In the case of Tektronix, some early logic analyzers were spinoffs from scopes. "The first logic analyzers were actually scope plug-ins," remembers Dave Holaday, an electrical engineer with Tektronix's logic-analyzer hardware engineering group.
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