Tektronix Addresses Real-Time Spectrum Analysis
Rick Nelson, Chief Editor -- Test & Measurement World, 10/10/2005 11:07:00 PM
Tektronix is tailoring its real-time spectrum-analyzer lineup to a variety of application areas by introducing software enhancements, the most recent ones being its signal-source analysis suite, introduced last week, and an RFID measurement suite, introduced last month. Bob Hiebert, director of marketing for real-time spectrum analyzers, discussed in an interview how, why, and where to perform real-time spectrum analysis.
According to Hiebert, real-time spectrum analysis is finding use in a variety of applications, from components like phase-locked loops and voltage-controlled oscillators to boards and systems. "RF gets into everything," he said, noting that component developers will need to look for spikes or spurs from their PLLs and VCOs but will also need to make sure the devices operate properly in board-level reference designs. In addition to being ubiquitous, he said, RF is transient in nature, generating a need for real-time spectrum-analysis tools.
Tektronix develops the measurement suites, he said, in response to customer demands for dealing with disruptive technologies. The signal-source analysis suite, for example, arose in part to satisfy requests of PLL designers who wanted to see how phase noise varies over time, while the RFID suite helped to address customers' efforts to comply with relevant RFID standards.
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Real-time spectrum-analysis applications extend far beyond traditional RF areas like phase-noise measurement, he noted. "RF is everywhere now," he said, emphasizing that "High-speed digital is now RF." The clock speeds now running on back planes, he said, correspond to what used to be known as microwave frequencies. He noted that consequently, Tektronix needs to address a couple of constituencies: the traditional RF engineer accustomed to looking at spectral phenomena like phase noise, and the digital engineer, used to looking at time-domain parameters like jitter.
Jitter and phase noise are mathematically related, he noted, but added that their traditional measurement approaches have major differences, with phase-noise measurements typically requiring significantly better noise performance on the part of the instrumentation. He added that it's ironic that real-time spectrum analyzers (traditional RF/microwave measurement champions) from his firm offer only 8-GHz real-time bandwidths, while oscilloscopes (traditionally applied to lower-speed time-domain investigations) from Tektronix offer 15-GHz performance. "The whole world seems upside down right now," he commented, adding that measurement suites are aimed in part at helping customers view that world in proper perspective.
He noted that Tektronix is addressing yet another constituency in addition to the traditional RF engineer and high-speed-digital developer. "One big source of RF problems these days is software bugs. A bad line of code in a DSP can lead to bad RF behavior. It creates interesting challenges for customer labs. The traditional RF person knows how to drive all the test equipment and knows what to look for. But for DSP software engineers right out of college, RF is a mathematical abstraction," and they face difficulties when they go into the lab and try to troubleshoot their designs. "So we are developing user interfaces that are both intuitive to the traditional RF engineer yet speak to the modern DSP engineer."
The history of real-time spectrum analysis, he said, goes back to the 1980s, when Tektronix configured a rack of equipment--used in military surveillance--that basically served as a baseband FFT engine. Enhancements in the early 90s added input downconverters. The technology became the responsibility of a Japan-based joint venture with Sony, which nurtured it along until Tektronix resumed full control of the operation early this decade. The technology has evolved to yield today's WCA200A, RSA3300A, and RSA3408A real-time spectrum-analysis instruments. (The Japan operation, which shares development duties with an engineering group in the Beaverton, OR, headquarters, is responsible for high-performance arbitrary waveform generators and digital timing generators as well as real-time spectrum analyzers.)
"In some cases users can take the data out of our box and do you their own analysis," he said, citing as an example audio distortion analysis using National Instruments' LabView or the MathWorks' Matlab. But some functions, such as displaying multi-domain time correlated views, can't be easily accomplished externally. "The ability to look at the frequency, time, and the modulation domains and possibly code domain and data domain as well and see at a particular point in time how a signal is behaving is where the real power of real-time apectrum analysis pops out." He noted that it can make it unnecessary to build special test modes into devices. In the case of Bluetooth, for example, designers have added modes that inhibit frequency hopping to facilitate test, "but that's not how the device is going to operate in the real world, he said.
He noted that real-time spectrum analyzers aren't ideal for every RF application. With a 36-MHz real-time acquisition bandwidth, they can't handle ultrawideband circuitry, which can span 500 MHz in a single hop and 1.5 GHz in a three-hop sequence. Similarly, thy don't equal the performance of dedicated phase-noise meters for crystal-oscillator tests. But, he said, in contrast to expensive, special-purpose boxes that are used once per project and then sit on the shelf for months, real-time spectrum analyzers are good general-purpose alternatives that can serve many applications.
Ultimately, he said, the goals are, first, to help customers find problems faster so they get to market sooner, and second, to help customers find problems before they ship products.
