Electronic Design
Scope, Spectrum Analyzers Score Best In Test For 2009

Scope, Spectrum Analyzers Score Best In Test For 2009

Test-equipment vendors improve on previous oscilloscope offerings each year, and 2009 was no exception. LeCroy’s WaveMaster 8 Zi series of digital oscilloscopes, serial data analyzers, and disk-drive analyzer are the company’s widest in bandwidth as well as its fastest real-time scopes. They provide a sample rate of 80 Gsamples/s, 512 Mpoints of analysis, and greater than 15-GHz edge triggering (Fig. 1).

The series comprises a single hardware platform with eight models spanning 4 to 30 GHz of bandwidth. As a result, engineers can stay current with emerging high-speed technologies and serial data standards by purchasing only the bandwidth needed for current designs and upgrading to additional bandwidth as needs change.

Oscilloscopes with bandwidths up to 30 GHz are needed to test the fastest emerging technologies in the most difficult measurement environments. Challenges that weren’t very pronounced at rise times of 50 ps, or bit rates of 2.5 Gbits/s and slower, become more problematic as rise times approach or drop under 25 ps and bit rates exceed 5 Gbits/s.

At these speeds, engineers face signal-integrity problems that were formerly limited to the microwave frequency domain, such as imperfect test fixtures and test circuit connections. In addition, engineers implementing the next generation of high-speed serial data standards face the challenge of faster and more complex signals.

Meanwhile, the serial data channel (interconnect, transmission line, and/or backplane) speeds have not kept up, leading to signal degradation issues in the channel. In addition, emerging serial data standards, such as USB 3.0, require simulation (emulation) of the signal transmission path to ensure reliable performance in all user environments. Lastly, serial data receiver hardware is specifically designed to equalize for signal degradation, yet engineers have no way of characterizing the performance of their measured signals with receiver equalization applied.

With exceptional instrument responsiveness, 10- to 100-times faster analysis processing time, a large 15.3-in., 16:9 high-definition touchscreen display (50% larger than 12.4-in. displays), and both 50-/1- M input capability, the WaveMaster 8 Zi series is the most versatile oscilloscope platform available for meeting these high-speed challenges, LeCroy says.

For serial data applications, eight serial data analyzer (SDA) models provide the same high bandwidth range (from 4 to 30 GHz), sample rate, and analysis memory capability (with 20 Mpoints/channel standard). Combined with LeCroy’s SDA II serial data analysis tools and standard 3.125-Gbit/s serial trigger, they provide unmatched capability for implementing and debugging emerging, high-speed serial data standards, such as PCIe 3.0 and USB 3.0.

The SDA 8 Zi serial data analyzers are based on the WaveMaster 8 Zi series oscilloscope and are equipped with double the standard memory to capture more unit intervals in the eye diagram. They include an enhanced high-speed serial pattern trigger that operates on up to 80 bit patterns and at speeds up to 3.125 Gbits/s.

Based on the WaveMaster 8 Zi series models, the DDA 8 Zi series disk-drive analyzers are available in 16- and 25-GHz models and come equipped with 20 Mpoints/channel of acquisition memory. Dedicated disk-drive measurements, trigger and zooming for failure analysis, and serial data measurement capability with a disk-drive analyzer user interface are also standard to address high-capacity disk-drive designs.

The instruments operate in either digital differential analyzer (DDA) or SDA mode to analyze the serial data links or the physical media behavior on a hard drive. All DDAs also offer all of the capabilities of SDAs, with the exception of the 3.125-Gbit/s serial trigger.

When selecting test equipment, design teams should be careful to consider whether an instrument can grow its capabilities to match their evolving needs. One of 2009’s best examples of an adaptable spectrum analyzer is Agilent’s N9030A PXA (Fig. 2).

Intended as an evolutionary replacement for Agilent’s PSA series signal analyzers launched in 2000, the N9030A PXA offers frequency coverage up to 26.5 GHz. It delivers up to 75 dB of spurious-free dynamic range (SFDR) at a 140-MHz bandwidth and reduces test time by 30% to 70% compared to older-generation instruments.

Furthermore, the N9030A PXA reduces measurement uncertainty through its ±0.19-dB accuracy. Its noise floor approaches that of thermal noise, with a displayed average noise level (DANL) specification of –172 dBm (with preamplifier) and closein phase noise of –128 dBc/Hz. As a result, Agilent has been able to accurately model the instrument’s generated noise and subtract it from measurements.

A broad set of applications and demodulation capabilities augments the PXA analyzer’s native capabilities, starting with one-button power measurements. Agilent’s 89600 VSA software adds measurement packages for more than 70 standard signal and modulation types. A host of additional applications is in the works. The Matlab integration offered on the low-cost N9000A analyzers applies to the N9030A PXA instrument as well.

Designers of high-frequency RF equipment and systems are finding that performance is everything when it comes to spectrum analysis. They need to be able to see small signals in the presence of large ones. Working with digital RF requires analysis with a combination of dynamic range and image rejection at very wide bandwidths.

All of these capabilities and more are manifested in the Tektronix RSA6120A spectrum analyzer (Fig. 3). It incorporates a feature set that directly targets digital-RF designers working in the Ku-band frequencies (12 to 18 GHz). The instrument also offers extremely high SFDR of 75 dB in the Ku-band and an enhanced set of radar measurements. Its switched-filter preselection overcomes the limitations of earlier spectrum analyzers.

Sporting a full 110 MHz of real-time bandwidth, the RSA6120A offers the industry’s best dynamic range in both wideband and narrowband measurements, according to the company. An important benchmark for narrowband performance is the third-order intercept spec (TOI).

The RSA6120A offers a TOI spec that’s 3 to 8 dB better than competing instruments, Tektronix says. The analyzer is specified for a TOI of +19 dB above 6 GHz. On the wideband side, it delivers impressive signal fidelity in the Ku-band.

The instrument’s roster of radar measurements includes new pulse statistics and histograms. It also features new pulse measurements, including overshoot, ripple, and droop. A total of 27 different automatic scalar and vector measurements is available on each radar pulse, all at the push of a single button. Its impulseresponse measurement provides automatic measurement of radar chirp quality. Users gain qualitative measurement of impedancemismatch problems in the signal chain.

A key to the RSA6120A analyzer’s performance is its application of microwave preselection in the signal-downconversion chain to narrow down to a band of interest from within a wideband window. While traditional preselector approaches use YIG-based (yttrium-iron-garnet) technology, this approach can cause phase and amplitude distortion by altering magnetic fields.

The RSA6120A also can introduce hysteresis when tuning across frequencies. Moreover, because YIG preselectors are inherently narrowband devices, wideband measurements cannot be made with the preselector inline. As a result, the instrument’s acquisition window is thrown open to images and other artifacts of upstream mixers.

Instead, the RSA6120A uses a switched-filter preselector, which offers wide frequency coverage and is always inline. Flatness across 100 MHz is specified at ±0.7 dB RMS and ±1.5° RMS. While switched-filter preselectors also introduce amplitude and phase errors, as do YIG filters, the errors introduced by a switchedfilter preselector are stable over time and temperature and can be characterized and compensated for in software.

So unlike the YIG preselector, the switched-filter preselector can be used for wideband signals. Because the preselector in the RSA6120A analyzer is always inline, radiation from its local oscillator (LO) into the RF signal chain is virtually eliminated.

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