Tracking down bugs in complex digital systems is a mighty challenge for design engineers, especially considering the rocketing speeds of microprocessors, buses, and other elements in these systems. To meet these challenges, manufacturers of logic analyzers are constantly improving the hardware and software of these sophisticated instruments.
Hardware improvements tend to make logic analyzers faster, wider, and deeper. Faster refers to an increase in state and timing speeds. Wider refers to an increase in the number of channels. Deeper refers to an increase in memory depth. Software improvements often enhance the instrument's usability.
We checked in with the two behemoths of the logic-analyzer domain, Tektronix Inc. and Agilent Technologies Inc., to find out how these instruments are improving, changing, and otherwise evolving to meet the demands of powerful new technologies. Pentium 4, PCI-X, double-data-rate (DDR) RAM, and Infiniband are just a few of these technologies that come to mind.
The key aspect of high-end logic-analysis systems, like the Tektronix TLA 700 series and the Agilent 16700 series, is their modularity (Fig. 1). Designers add modules to their systems whenever they need more channels or require the functionality that comes from adding an oscilloscope or pattern generator to the system. If more slots are necessary, an expansion chassis can be added to the base system. As you might guess, these logic analyzers come with a high price tag.
Why would a designer add more channels to the system? This technique is one way to get an instrument with a 200-MHz state speed to analyze, for example, a bus with, say, a 266M-Hz or higher speed. Logic analyzers deal with the speed issue through a combination of speed and channels. In fact, if you want to know what speed an analyzer can handle, just multiply its speed by its number of channels, a specification usually referred to as data bandwidth.
There's more to it, of course. Usually, the logic analyzer performs some electronic magic in the front end, such as multiplexing, to make everything work correctly. The overall trend, though, is the slow but steady march of state speed and channel capacity in logic analyzers. Last May, for instance, Agilent announced three new state- and timing-analysis modules for its 16700 series that have a state speed of 400 MHz. On the other hand, Tektronix introduced its TLA7XM expansion mainframe about a year ago (Fig. 2).
Adding this single expansion unit to the TLA 700 increases the number of logic-analyzer channels of the combined system to 2176, while the maximum number of channels possible is a whopping 8160. This large number of channels is especially needed when acquiring and analyzing data from multiple processors and buses in a single system, and it addresses the complex verification challenges associated with these high-end systems.
Riding hot on the heels of faster and wider is the feature known as deeper, meaning greater memory depth. Both Agilent and Tektronix claimed gains in this area last year. Agilent's new 16752A state and timing module, for example, offers a memory depth of 32 Msamples, while Tektronix's recently announced TLA7Q2/4 acquisition modules bring the memory depth of the TLA 700 Series up to 64 Msamples from only 16 Msamples (Fig. 3).
Greater memory depth is valuable, for instance, when working with communications protocols. The larger the memory, the greater ability it has to capture entire frames or packets of data.
There's another reason why manufacturers are constantly improving the memory depth of logic analyzers. The advent of simulators, which enable a lot more work to be done prior to the actual prototype, together with the process improvements in the levels of integration—meaning smaller and smaller transistors and larger and larger chips—are producing more complex designs. As Colin Shepard, general manager of the logic analyzer product line at Tektronix, puts it, "The good news is that we can even contemplate doing that complex of a design because we have better simulation tools. But the reality is, the problems that show up on the prototype are that much harder to find."
Due to the high levels of integration, when a problem occurs, its cause actually took place a while ago. This is why designers require greater and greater memory depth. "It just seems like there's an insatiable appetite for that. The greater the memory depth, the further backward in time designers can look from the trigger on that glitch to see what the real cause was, and see what sequence of events led up to the problem," Shepard remarks.