The increasingly complex modulation formats of emerging communications standards supports a more flexible, modular approach to future measurement equipment.
Test equipment is the great enabler for developers of high-frequency components, devices, and systems. It must be accurate and reliable, and not impossible to use or program. Instrumentation has evolved over the most recent decade to reach new levels of power and flexibility, with the most dominant trend the increasing role of the embedded microprocessor for command, control, and data manipulation. What follows is a brief review of some recent trends in high-frequency measurement equipment and associated software.
As an overall trend, instruments continue to leverage the processing capabilities of microprocessors and digital signal processing (DSP) for increased measurement power. As an example, consider the fact that LeCroy Corp. (www.lecroy.com) now offers standard sampling rates of 5 GSamples/s in their 400- and 600-MHz WaveRunner Xi real-time oscilloscopes (see p. 88), and shows waveforms on a bright 10.4-in. liquid-crystal-display (LCD) screen that contributes to an instrument depth of only 6 in.
At higher-frequencies, Tektronix recently announced the DPO7000 series additions to their lines of digital phosphor oscilloscopes (DPOs). The new line includes the 500-MHz DPO7054, the 1-GHz DPO7104, and the 2.5-GHz DPO7254. The new scopes make use of silicon-germanium (SiGe) front-end technology to capture transient signals over broad bandwidths. The DPO7254 offers sampling rates of 10 GSamples/s on four channels, with interleaved sampling capability of 40 GSamples/s when only one channel is used. The DPOs feature a slightly larger display screen than the vivid LCDs of the LeCroy instruments, with 12.1-in. XGA displays. Prices begin at $14,000 US for the new DPOs.
In terms of pure scope power, LeCroy's WaveExpert series of oscilloscopes includes models with bandwidths to 100 GHz (Fig. 1). The scopes make use of a front end based on the nonlinear-transmission-line (NLTL) technology from Picosecond Pulse Labs (www.picosecond.com) to achieve the broad bandwidths. These sampling oscilloscopes feature 20-ps time-domainreflectometry (TDR) rise time of better than 20 ps and acquisition rates of 10 MSamples/s.
Instruments are getting smaller while maintaining measurement power, such as the VNA Masters from Anritsu Co. (www.us.anritsu.com). In spite of their battery-powered, palm-sized packages (Fig. 2), these are full-function, two-port vector network analyzers that include 2-MHz-to-4-GHz and 2-MHz-to-6-GHz models (see Microwaves & RF, December 2005, p. 88).
Last year, Advantest (www.advantest.com) announced its models U3771 and U3772 portable spectrum analyzers with starting frequencies of 9 kHz and top frequencies to 31.8 and 43 GHz, respectively. Weighing only 6 kg and measuring 308 175 209 mm, the analyzers can run on AC/DC power or rechargeable batteries for satellite and terrestrial communications monitoring.
The FSH3 and FSH6 instruments from Rohde & Schwarz (www. rohdeschwarz.com) also pack full microwave spectrum-analysis capabilities into handheld packages. Operating to top frequencies of 3 and 6 GHz, respectively, the analyzers offer resolution bandwidths from 100 Hz to 1 MHz with a wide range of signal detectors. They achieve a displayed average noise level of typically ?135 dBm at a resolution bandwidth of 100 Hz. The compact instruments measure only 120 95 39 mm and weigh only 0.65 kg.
Microwave test companies once consisted of a handful of suppliers, including Hewlett-Packard Co. (now Agilent Technologies) and Wiltron (now Anritsu). The list has grown considerably over the years, with companies once considered more for software or DC/ parametric test, such as National Instruments (www.ni.com) and Keithley Instruments (www.keithley.com). Keithley Instruments offers a wide range of RF/microwave switching solutions, including the model S46 switching system with bandwidth of 18 or 40 GHz and as many as 32 switching channels. The 2U-high rack-mount system is designed to simplify switching tasks in automatic-test-equipment (ATE) systems and provides simple control with built-in GPIB port.
National Instruments, perhaps best known for its LabVIEW programming software used by many test engineers, has added RF/microwave instruments in modular format, including the PXI-5671 vector signal generator and the PXI-5660 vector signal analyzer. Both are supplied in the plug-and-play PXI format and work with National's various software tools.
The PXI-5671 is a vector signal generator that upconverts digitally produced signals. It operates from 250 kHz to 2.7 GHz with a 20-MHz real-time bandwidth and can produce a wide range of modulation formats, including AM, FM, ASK, FSK, MSK, GMSK, QPSK, and QAM. The module can control output levels from ?145 to +10 dBm. The PXI-5660 is essentially the analysis version of the first module, with a 20-MHz real-time bandwidth over a range of 9 kHz to 2.7 GHz. It is essentially a 2.7-GHz downconverter with a 14-b, 64-MSamples/s digitizer that provides a spurious-free dynamic range (SFDR) of better than 80 dB.
These "instrument-on-a-card" represent another trend in test, toward the modular system or even toward a software-programmable system as embodied in the synthetic instruments. The US Department of Defense (DoD) has pushed manufacturers to develop instruments based on modular hardware and reconfigurable software called synthetic instrumentation (SI) as a way or reducing test costs. Synthetic instruments, which employ standard interfaces with elemental hardware and software tools, differ somewhat from virtual instruments (VI), in which software defines the function of generic hardware (such as a digitizer used as a spectrum analyzer).
Last year, Agilent Technologies unveiled a line of SI products (see Microwaves & RF, August 2005, p. 78) that included the N8241A arbitrary waveform generator and the N8201A frequency downconverter. The waveform generator features a pair of 14-b, 1.25-GSamples/s output channels that can be used for single-ended or differential outputs with bandwidths of 500 MHz per channel or 1 GHz as a single channel. The downconverter translates input signals from 3 Hz to 26.5 GHz to intermediate-frequency (IF) outputs at 7.5, 21.4, and 300 MHz. The instruments offer compliance with the LAN eXtension for Instrumentation (LXI) standards to allow interoperability with other manufacturers' modular instruments.
In addition to military support for modular instruments, some suppliers are looking toward that format for commercial solutions as well. Last year, Aeroflex (www.aeroflex.com) introduced a PXI-based measurement suite for WLAN integrated-circuit (IC) testing. The firm's PXI 3000 series instruments, which are also available for evaluating GSM/EDGE ICs, are based on the model 3030 PXI digitizer and several new test sources.
In an even more compact modular format, some instruments are migrating to a personal-computer (PC) platform, such as the PicoScope 3000 oscilloscopes from Pico Technology (www.picotech.com). These miniature modules are about the size of a VHS tape, but pack two measurement channels with 10 GSamples/s sampling rate over a 200-MHz input analog bandwidth.
Acqiris (www.acqiris.com) offers one of the more extensive lines of PCI and compact PCI (cPCI) card-based signal analyzers and digitizers, including the AP240 PCI signal analyzer with sampling rates from 1 to 2 GSamples/s, two measurement channels, and 1-GHz bandwidth. The high-speed PCI bus handles data transfers to 100 Mb/s, and the company offers a wide range of software drivers, with support for Windows 98/NT4/2000/XP, Linux, and Wind River VxWorks. The firm also offers a wide range of digitizer cards with choice of 8-, 10-, and 12-b resolution.