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Electronic Design

Test Instruments Stay Ahead Of The Curve

The latest spectrum analyzers, oscilloscopes, and network analyzers give designers the weapons to eliminate bugs from next-gen systems.

Maintaining one’s competitive edge in this economic downturn often comes down to the tools used to get the job done. In terms of test instruments, this is especially true.

Without oscilloscopes, spectrum analyzers, and other instruments with the speed and bandwidth to capture today’s high-speed serial bus traffic, it’s virtually impossible to verify the performance of many systems. On top of that, the same instruments are essential to ensure that these systems comply with protocol standards for those serial buses.

So here’s a look at some of today’s latest, and highest-performing, laboratory-grade test instruments. Some of these machines are pricey indeed, but their prices pale in comparison to the cost of missing a market window or being denied standards certifications.

These days, test instruments often are called upon for more than one task. Thus, instrument makers are routinely expected to package the capabilities of more than one instrument in a single box. Not only that, but each blade of that Swiss-army-knife instrument has to be at least as sharp as it would be in a high-end standalone version.

Agilent’s latest additions to the upper reaches of its scope lineup achieve this trick handily. The six models that comprise the Infiniium 9000 series sport true analog bandwidths up to 4 GHz. Not only that, the scopes also are fitted with the industry’s largest screens: a 15-in. XGA LCD (Fig. 1).

Designers of high-end embedded systems typically need scopes with bandwidths of at least 1 GHz these days. Users have a range of requirements with respect to oscilloscopes, not necessarily knowing what kinds of measurement tasks they may have from day to day. “Protocol issues, debug challenges, and questions of compliance are common to many designs,” says Richard Markley, Infiniium sales manager at Agilent. Further, engineers often find themselves with limited bench space and shared oscilloscopes.

To address that need for a multifaceted instrument, the Infiniium 9000 series instruments are essentially three instruments in one: an oscilloscope, a logic analyzer, and a protocol analyzer. As an oscilloscope, the Infiniium 9000 series enables users to quickly visualize signals, providing fast autoscaling and drag-and-drop measurement capabilities. It delivers precision and parametric detail, with standard sample rates of up to 20 Gsamples/s. At the same time, it enables captures of long signal traces—10 Mpoints worth of memory is standard, and up to 1 Gpoint worth is optional.

In addition to their analog specifications, the units offer 16 integrated digital channels running at 2 Gsamples/s. These mixed-signal oscilloscope (MSO) channels function as a logic analyzer, allowing users to view or trigger on data buses or control signals to observe and analyze digital timing relationships. These capabilities permit quick debugging of systems with FPGAs or embedded microprocessors/ microcontrollers.

Because almost all designs integrate serial communications protocols and/or high-speed serial channels such as PCI Express, Agilent endowed the Infiniium 9000 series with a set of protocol analysis capabilities. “Not only can you see the physical layer, but you can go up into the protocol stack and see the packets being passed around,” says Markley. “This can help you tell if problems are related to the protocol itself or something else.”

With in-scope protocol viewers for USB and PCI Express, engineers can extend their debug and testing reach without the need to hook up additional instruments. Users can see serial packet contents, trigger at the protocol level, and non-intrusively debug these serial buses. Packets are viewable down to bit level to isolate faults to analog or logic sources.

With the scopes comes a broad range of debug and compliance software that optionally supports up to 25 different applications. These give designers meaningful insights into common serial buses, FPGAs, and RF measurements, allowing for quick compliance testing. debug applications include protocol triggering and viewing for PCI Express and USB; serial decode and triggering for i2c, SPI, CAN, and RS-232 buses; and core-assisted debug of designs with Altera or Xilinx FPGAs.

The prevalence of digital RF technology in many systems has created some interesting test challenges. digital RF is an environment combining gigahertz signals with mixed-signal complexities, in addition to digital baseband having to translate over into the RF domain. Typically, multiple radios come within a single platform. signal bursting and hopping combine with transients to make verification and troubleshooting a difficult task.

That’s roughly where Tektronix’s enhancements for its RSA6000 series of spectrum analyzers enters the picture. in 2006, the company added its DPX spectrum processing technology to these instruments, enabling users to observe and analyze these kinds of phenomena.

Tektronix recently upgraded the scopes again, adding swept spectrum analysis to the DPX transform engine. The resulting transformational swept DPX capability provides wideband signal search with the highest probability of detection available.

The DPX engine collects hundreds of thousands of spectrum sweeps per second over a bandwidth slice of 110 MHz. As a result, the engine can be swept across the full input range of the RSA6000 series (up to 14 GHz). Further, a user-defined dwell-time setting allows designers to “stare” at bands of interest to capture transients at each point in the sweep.

For example, in analyzing a 10-ns impulse signal, the RSA6000 instruments can zero in on internal interference within the pulse generator (Fig. 2). This example shows a bandwidth of 1 GHz, demonstrating their ability to take DPX triggering to a wideband stage.

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Augmenting the DPX spectrum processing technology in the upgraded analyzers is DPX density triggering, which lets users trigger on “signals within signals” that are obscured by traditional analyzers. with this capability, designers can isolate random, low-level events. examples include sources of self-interference in radar and electronic warfare applications.

Tektronix further enhanced the analyzers with its second-generation DPX live RF spectrum display. This provides more than a sixfold increase in the update rate, which translates into an update rate of 292,000 spectrums per second. it also means a 100% probability of intercept for signals of just 10.3 µs.

“if you had a 2-µs event, the analyzer would still show it with 100% probability, but the amplitude would be at 20% of the level of the 10.3-µs signal,” says darren mccarthy, RF technical marketing manager at Tektronix.

Anyone who’s ever had to integrate and maintain the systems required to test transmit/ receive modules, converters, and amplifiers in the aerospace and defense market knows that these systems are massive. multiple racks full of instruments must be deployed to run the hundreds of tests usually conducted on a typical transmit/receive module. These modules are often tested under hundreds of different test conditions in both linear and nonlinear operating conditions.

To address these requirements, Agilent expanded its PNA-X series of network analyzers to include 43.5- and 50-GHz models (Fig. 3). with double the frequency coverage of existing PNA-X analyzers, highly integrated and versatile hardware, and reconfigurability by means of internal switch banks, these instruments can potentially replace a large portion of those multiple racks of instruments. Functions now included within the PNA-X instruments include vector network analysis, signal sources, spectrum analysis, pulse pattern generators, pulse modulators, and switch matrices.

when it comes to active device tests for wireless communications, Agilent provides a 13.5-GHz version of the PNA-X. in the wireless arena, active devices such as power amplifiers, low-noise amplifiers, front-end modules, and up/down converters are tested at a series of test stations for different requirements. These include small-signal s parameters for linear performance, high-power gain or pulsed RF stimulus, distortion, and noise figure. Again, the 13.5-GHz PNA-X comprises a single test station that makes the test process extremely efficient.

Because the PNA-X is so highly integrated, it enables multiple measurements with one connection. This benefit takes on greater importance in on-wafer device tests. in typical test setups involving multiple stations, the act of attaching probes can scratch device bonding pads to the point where subsequent wire bonding suffers. The PNA-X sidesteps this potential for damaging devices in the testing process.

Agilent also released nonlinear vector versions of the 43.5- and 50-GHz network analyzers, which deliver accurate nonlinear characterization of higher-frequency devices. These instruments, claimed by Agilent as industry firsts, are based on the standard PnA-X units, so they also incorporate all of the linear measurement capabilities.

in nonlinear mode, all of the input and output spectra of the device under test (DUT) are measured. Both the amplitude and phase of the full spectra, including fundamental, harmonics, and cross-frequency products, are displayed. relative phase and absolute amplitude of any of the frequencies of interest can also be displayed.

One interesting potential application of the nonlinear analyzer is the creation of X-parameter models for use within Agilent eesof’s Advanced design system, which simulates actual linear and nonlinear component behavior. in traditional top-down design specifications, precious little is shared with ic designers to describe how the chip should behave in typical operating conditions. That results in a tedious, iterative process of tweaking to satisfy system-level performance requirements.

A better methodology is for network equipment manufacturers to use the nonlinear analyzer to generate X parameters that describe much more comprehensive systemlevel performance requirements (Fig. 4). These requirements can be shared with IC designers without providing detailed specifications for all operating conditions. Then, during the IC design cycle, the IC designers can send back their own X parameters to the equipment manufacturers for verification before prototyping.

During the prototyping phase, designers can use those same X parameters to thoroughly simulate the IC’s responses to various realworld operating conditions. These X parameters accurately represent the responses and are transferable to the circuit-level or system-level simulation so the equipment designer can effectively optimize system-level performances with little iteration.

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