Originally posted Apr 18, 2016
Get all the signal analyzer performance you pay for
After perusing a pair of new application briefs, I was impressed by the improvements in signal analyzers driven by the combination of evolving semiconductor technology and plain old competition. I’ll write a little about the history here, but will also highlight a few of the benefits and encourage you to take advantage of them as much as possible. They’ll be welcome help with the complex signals and stringent standards you deal with every day.
Intel’s Gordon Moore and David House are credited with a 1960s prediction that has come to be known as Moore’s law. With uncanny accuracy, it continues to forecast the accelerating performance of computers, and this means a lot to RF engineers, too. Dr. Moore explicitly considered the prospects for analog semiconductors in his 1965 paper, writing that “Integration will not change linear systems as radically as digital systems.” *
Note that as radically qualifier. Here’s my mental model for the relative change rates.
Comparing the rate of change in performance over time of the semiconductor-based elements of signal analyzers. Processors have improved the fastest, though analog circuit performance has improved dramatically as well.
In analyzer architecture and performance, it seems sensible to separate components and systems into those that are mainly digital, mainly analog, or depend on both for improved performance.
It’s no surprise that improvements in each of these areas reinforce each other. Indeed, the performance of today’s signal analyzers is possible only because of substantial, coordinated improvement throughout the block diagram.
Digital technology has worked its way through the signal analyzer processing chain, beginning with the analog signal representing the detected power in the IF. Instead of being fed to the Y-axis of the display to drive a storage CRT, the signal was digitized at a low rate to be sent to memory and then on to a screen.
The next step—probably the most consequential for RF engineers—was to sample the downconverted IF signal directly. With enough sampling speed and fidelity, complex I/Q (vector) sampling could represent the complete IF signal, opening the door to vector signal analysis.
Sampling technology has worked its way through the processing chain in signal analyzers. It’s now possible to make measurements at millimeter frequencies with direct (baseband) sampling, though limited performance and high cost mean most that RF/microwave measurements will continue to be made by IF sampling and processing.
This is where competition comes in, as the semiconductor triple-play produced an alternative to traditional RF spectrum analyzers: the vector signal analyzer (VSA). Keysight—then part of HP—introduced these analyzers as a way to handle the demands of the time-varying and digitally modulated signals that were critical to rapid wireless growth in the 1990s.
A dozen years later, competitive forces and incredibly fast processing produced RF real-time spectrum analyzers (RTSAs) that calculated the scalar spectrum as fast as IF samples came in. Even the most elusive signals had no place to hide.
VSAs and RTSAs were originally separate types of analyzers, but continuing progress in semiconductors has allowed both to become options for signal-analyzer platforms such as Keysight’s X-Series.
This takes us back to my opening admonition that you should get all you’ve paid for in signal analyzer performance and functionality. Fast processing and digital IF technologies improve effective RF performance through features such as fast sweep, fast ACPR measurements, and noise power subtraction. These capabilities may already be in your signal analyzers if they’re part of the X-Series. If these features are absent, you can add them through license key upgrades.
The upgrade situation is the same with frequency ranges, VSA, RTSA, and related features such as signal capture/playback and advanced triggering (e.g., frequency-mask and time-qualified). The compounding benefits of semiconductor advances yield enhanced performance and functionality to meet wireless challenges, and those two new application briefs may give you some useful suggestions.
* “Cramming more components onto integrated circuits,” Electronics, Volume 38, Number 8, April 19, 1965