In the test and measurement market, the “best” of anything is subjective. Specsmanship abounds in the test arena. But when it comes to oscilloscopes, bandwidth most quickly catches the eye of designers of bleeding-edge circuits.
Thus, at the top of the list of this year’s best test instruments is LeCroy’s WaveMaster 8Zi-A, which the company touts as the world’s highest-performance four-channel oscilloscope (Fig. 1). The scopes are upgradable from 4 GHz to a maximum 45 GHz in bandwidth with a sampling rate of 120 Gsamples/s. That’s combined with 768 Mpoints of analysis memory. The sampling-rate breakdown is 120 Gsamples/s at 45 GHz, 80 Gsamples/s for bandwidths of 25 to 30 GHz, and 40 Gsamples/s on all four channels at a 20-GHz bandwidth.
The scopes’ improved performance is attributable in part to a second-generation silicon-germanium (SiGe) chipset that not only provides the increased bandwidth, but also improves the earlier scopes’ signal-to-noise performance by about 25%. The new scopes’ time-interval error (TIE) jitter noise floor is just 125 fsRMS, and stability for acquisitions greater than 10 µs is 175 fsRMS.
As with LeCroy’s previous WaveMaster scopes, the 820Zi-A uses the company’s digital bandwidth interleave (DBI) technology to achieve the high bandwidths. Input signals are divided into two frequency bands, with the dc to 20-GHz portion routed through one digitizer while the 20- to 40-GHz range is digitized after being downconverted.
The two signal paths are post-processed, mixed back up in frequency digitally, and recombined. The result is double the bandwidth by using two channels. The 45-GHz 845Zi-A takes DBI to another level by interleaving three channels.
This is the secret to the scope’s inherent upgradability, which is accomplished simply by the addition of a high-speed RF deck. This amounts to investment protection, says Mike Schnecker, LeCroy’s business development manager for vertical markets.
According to Schnecker, the WaveMaster 8Zi-A scopes are significantly faster than the current high-end offerings from Agilent and Tektronix when it comes to performing demanding analysis tasks. This is due to their deep analysis memory and quad-core analysis processing engine, which runs at an effective CPU speed of 12 GHz. For example, an eye-pattern diagram of 100 unit intervals/s can be completed in 284 unit intervals/s, or about half a second.
The WaveMaster 8Zi-A scopes aren’t inexpensive, starting at $68,490 for a basic 4-GHz model and topping out at $268,000 for a fully loaded 45-GHz version.
Another formidable scope
Introduced last spring, Agilent Technologies’ Infiniium 90000 X-Series oscilloscopes sport real-time bandwidths of up to 32 GHz, which promises to meet the needs of engineers working with emerging wireline communication standards, high-speed serial data links such as USB, SAS, or PCI Express, or high-energy physics (Fig. 2).
Continue on next page
Along with their high bandwidths, the series offers up to 2 Gpoints of memory and a maximum sampling rate of 80 Gsamples/s. There are 10 models in the series with bandwidths of 16, 20, 25, 28, and 32 GHz.
Accuracy in jitter measurements at high speeds requires a scope that offers both high bandwidth and a low noise floor. The 90000 X-Series scopes offer an extremely low jitter measurement floor of about 180 fs as well as the lowest noise floor (2 mV at 50 mV/division, 32 GHz).
One element of the “secret sauce” that gives these scopes their capabilities is Agilent’s investment in a proprietary indium-phosphide (InP) process technology optimized for RF and high-performance scopes. The scopes’ front-end chips, which are fabricated on that process, are packaged in a multi-chip module where they’re embedded inside a substrate for improved shielding and grounding. Packaging the front end in this fashion also minimizes wirebond lengths, which in turn minimizes inductances and helps to hold down the noise floor.
The front end includes two new preamplifiers rated to 32 GHz as well as two edge-trigger chips with about 22 GHz of edge-trigger bandwidth, lending the scopes nicely to radar applications. Also, a new 32-GHz sampling chip requires no digital bandwidth interleaving or DSP boosting to reach the rated bandwidth. Both of those techniques introduce increased noise density, cause measurement inaccuracies, and result in nonlinear frequency response. In contrast, not only does this front end deliver superior pulse distortion control and significant margins in speed and fidelity, it also offers headroom for higher speeds in the future.
To help designers get the most out of these scopes, Agilent offers a comprehensive lineup of application-specific measurement packages, including a broad range of jitter, triggering, analysis, and display tools as well as pre-built compliance-testing software. The software is put together with the aid of Agilent engineers who serve on the standards committees in question. The packages support emerging high-speed serial-bus standards including the QuickPath interconnect, Fibre Channel, SAS 12G, and 10-Gbit/s Ethernet.
Prices start at $131,000 for a two-channel, 16-GHz model and range up to $286,000 for the high-end version.
A VNA goes pxi
Hitting a dual sweet spot of modularity and wireless design, the National Instruments NI PXIe-5630 is the industry’s first vector network analyzer (VNA) in a compact PXI form factor (Fig. 3). The 6-GHz, two-port instrument brings support for full vector analysis of transmission and reflection (T/R) parameters.
Featuring precision automatic calibration and a flexible software-defined architecture, the VNA suits automated design validation and production test. With its modular PXI architecture and small, two-slot footprint, engineers can incorporate vector network analysis into their test systems without the cost and large footprint of traditional benchtop VNAs.
According to Richard McDonell, senior group manager in product marketing at National Instruments, the NI PXIe-5630 represents NI’s ongoing efforts to address emerging automated test needs in a decade that will be dominated by the proliferation of embedded wireless capabilities. “The NI PXIe-5630 fills out our RF test platform,” says McDonell. Traditional VNAs are too large and too costly to deploy in production-test environments. The PXI instrument answers those needs by combining elements of both low-end and high-end VNAs in a form factor that works in the production environment.
Continue on next page
The NI PXIe-5630 is optimized for automated test with a mature feature set including automatic precision calibration, full vector analysis on both ports, reference plane extensions, and a flexible LabVIEW application programming interface (API) that suits parallel test. The VNA also delivers advanced performance specifications including a frequency range of 10 MHz to 6 GHz, a wide dynamic range of greater than 110 dB, and sweep speeds of less than 400 µs/point over 3201 points. Additionally, because of its PXI configuration, engineers can combine up to eight NI PXIe-5630 modules in a single PXI chassis and perform multisite RF test in true parallel fashion.
Engineers can control the NI PXIe-5630 interactively using its full-featured soft front panel or programmatically using APIs for NI LabVIEW software and NI LabWindows/CVI ANSI C development environments. Both APIs are optimized for multicore processing to facilitate parallel test of multiple RF components, which provides a significant throughput advantage over sequential, switched testing. Pricing for the PXIe-5630 starts at $25,999.