Instruments Contend with Exploding Data Bandwidth

Whether you need to transmit and receive data over a few millimeters of PCB trace or across an ocean, you can choose from a variety of instruments and software to test how well your data-communications link is working. To address applications ranging from I²C to 400 GbE and beyond, vendors are debuting new instruments, upgrading existing ones, and introducing software enhancements to handle challenging data-communications measurement tasks.

Those instruments include oscilloscopes, arbitrary waveform generators, bit-error-ratio testers, vector network analyzers, and a variety of software options that support the analysis of copper and optical data-communications links. With respect to the latter, companies beginning to deploy 100G data-communications systems are simultaneously facing the need to develop systems that operate at 400 Gb/s and even 1 Tb/s and beyond. To achieve higher speeds, instead of increasing the symbol rate of a single carrier, one approach is to transmit signals in parallel by using multiple carriers at lower individual rates. Such multicarrier systems are called superchannels.

Arbitrary Waveform Generator

Tektronix is addressing the gamut of data-communications test applications from high-speed serial buses to superchannels with its new AWG70000 Series arbitrary waveform generators (Figure 1), introduced in March, which offer up to 50-GS/s sample rate performance. The new instruments support a range of signal-generation requirements in defense electronics, high-speed serial, optical networking, and advanced research applications. Multiple units can be synchronized to increase channel count to serve applications involving, for example, high-speed I/Q signal generation for optical transmission test or for HDMI 2.0 testing.

Figure 1. AWG70000 Series Arbitrary Waveform Generator
Courtesy of Tektronix

Justin Panzer, business development manager at Tektronix, said the instrument supports the high-speed communications of IEEE GbE as well as high-speed serial buses such as PCI Express, SATA, HDMI, DDR3, and DisplayPort. He also noted that the instrument accommodates wideband RF technologies (which will be the subject of a special report next month).

High-speed communications applications are seeing exponential growth in bandwidth demand, Panzer said, as long-range data networks struggle to keep pace with the face-time requirements of video-on-demand and videoconferencing. The increasing bandwidths, in turn, imply increasingly complex modulation schemes to improve transmission efficiency, he said, while higher clock and data-channel speeds drive tighter timing margins—all of which require wider bandwidth, higher resolution signal-generation capability for effective test.

Panzer said researchers at Bell Labs have employed the AWG70000 to generate signals for advanced research involving 1.5-Tb/s superchannel transmission over ultra-long-haul optical-fiber distances. Panzer quoted S. Chandrasekhar, one of the lead Bell Labs researchers on this project, as saying, “The sampling rate of 50 GS/s combined with the ability to synchronize two AWGs enabled us to generate 30-Gbaud signals per optical carrier, with a data rate of 233 Gb/s, more than twice the previous record.” The researchers cited the AWG70000’s performance and signal purity as key factors that helped meet the requirements for the 1.5-Tb/s experiment.

Panzer also cited the shift from slow, wide parallel buses to narrow, multigigabit-per-second high-speed serial buses, noting, “Applications that have been just around the corner are finally becoming a reality.” The emergence of such buses, however, is accompanied by a proliferation of standards as well as faster edges and slew rates, he said, with consequent impacts on EDA tools, packaging, PCB design, and test tools. As for test tools, he said, the new AWG70000 Series provides the signal-generation capability necessary to perform stress and margin testing.

In addition to 50-GS/s performance, Panzer said, the new AWGs offer up to 80-dBc spurious dynamic range and 16-GS of waveform memory. The instruments, he said, can generate wideband baseband singles for coherent optical testing using up to PAM16 signaling. They also support serial data signals up to 12 Gb/s. SerialXpress waveform-generation software facilitates the instruments’ use in design, debug, characterization, and compliance testing of high-speed serial data receivers; the software includes support for SATA, PCIe, SAS, DisplayPort, Fibre Channel, HDMI, USB, and MIPI receiver testing.

400G Systems

Tektronix also is offering products that focus specifically on optical communications. Robert A. Marsland, product line manager for optical products at Tektronix, said challenges facing developers looking to implement superchannel technology include variations in current proposals for implementing coherent optical systems—proposals vary considerably with regard to number of carriers, carrier spacing, and modulation format used. Consequently, he said, developers need test equipment that offers the flexibility to support any combination of system parameters.

Marsland, who came to Tektronix with its acquisition of Optametra, cited several examples of how vendors are looking to achieve high data rates, including 400 Gb/s using two channels and DP-16QAM, 500 Gb/s using five or 10 channels and DP-QPSK modulation, 1 Tb/s using 10 channels and DP-QPSK modulation, and 1.5 Tb/s using eight channels and DP-16QAM. “There is no industry consensus on how to build superchannels,” he said in a phone interview.

To support developers investigating multiple combinations of channel count, channel spacing, and modulation capability, Marsland said, Tektronix is offering a software option dubbed MCS on its OM-Series coherent lightwave signal analyzers that, in turn, are tightly integrated with Tektronix DPO70000D Series 33-GHz oscilloscopes and DSA8300 Series 70-GHz sampling oscilloscopes. Marsland said the instruments and new software option support unlimited user-definable superchannel definitions and reduced test times.

The software can present integrated multicarrier measurement results that facilitate channel-to-channel comparisons. Users can view eye diagrams, constellation diagrams, and optical spectrum plots, and channels can be superimposed for easy comparison.

The software also supports test automation. With multiple carriers defined in a multicarrier setup table (no carrier fixed grid is imposed so carrier width can vary from carrier to carrier), a single run command initiates all testing.

Test at DesignCon

Since EE’s last special report on serial data-communications test,¹ companies including Tektronix, Agilent Technologies, Anritsu, National Instruments, and Teledyne LeCroy have introduced products to support the task, and many of the products have been featured at shows—notably DesignCon in late January.

For example, National Instruments highlighted its new NI PXIe-5162 digitizer and updates to the LabVIEW Jitter Analysis Toolkit at DesignCon. The digitizer, with 10 bits of vertical resolution and a 5-GS/s sample rate, provides high-speed measurements at four times the vertical resolution of a traditional 8-bit oscilloscope. With 1.5 GHz of bandwidth and four channels in a single slot, the NI PXIe-5162 is suited for high-channel-count digitizer systems in manufacturing test, research, and device characterization. Engineers can use the digitizer with LabVIEW and the LabVIEW Jitter Analysis Toolkit, which provides a library of functions optimized for performing the high-throughput jitter, eye-diagram, and phase-noise measurements demanded by automated validation and production test environments.

The NI PXIe-5162 features four channels in a single 3U PXI Express slot, expanding to 68 channels in a single PXI chassis, and a 5-GS/s maximum sample rate on one channel or 1.25 GS/s on four channels simultaneously. The LabVIEW Jitter Analysis Toolkit incorporates built-in functions for clock recovery, eye diagram, jitter, level, and timing measurements as well as sample programs for eye diagram and mask testing and random and deterministic jitter separation using both dual-Dirac and spectrum-based separation methods.

Anritsu conducted demonstrations of its 32-Gb/s test solution featuring the Anritsu MP1800A BER testers at DesignCon. The MP1800A features the performance—including low intrinsic clock jitter of <350 fs (rms) and a unique eye contour function—necessary for engineers to evaluate jitter, ISI, and crosstalk at signals up to 32 Gb/s and employ necessary countermeasures to ensure signal integrity. The demonstration showed how engineers can use the solution to account for signal-integrity reduction for the transmitter and receiver circuits, ensuring the quality of the output signal and receiver tolerance to validate backplane and high-speed interface performance.

Also on display at DesignCon were Anritsu’s MP2100 BERTWave all-in-one BERT and EYE/Pulse scope solution and the MS9740A optical spectrum analyzer for evaluating XFP/SFP-type optical modules, laser devices, and optical cables used in optical communications systems. The MP2100 combines a BERT and sampling oscilloscope to reduce gating time by 90% compared with conventional BERT equipment, and the EYE/Pulse scope function is 300% faster. The MS9740A can measure optical devices in <0.2 s and has ≥58-dB dynamic range.

And at DesignCon Agilent Technologies announced an enhanced solution for PCI Express 3.0 receiver characterization. The PCIe 3.0 receiver characterization solution provides complete and accurate receiver tolerance test results while minimizing R&D effort. The new J-BERT software (revision 7.40) enables testing of PCIe 3.0 receiver designs that adjust the length of the 128b/130b encoded filler symbols—also known as SKP ordered sets—as needed for clock compensation.

Using the Agilent test set, design and test engineers in the semiconductor and computer industries can accurately characterize and verify standard compliance of PCIe receiver ports in ASICs, add-in cards, and motherboards.

Finally, Rohde & Schwarz announced at DesignCon that the R&S ZNB network analyzer now employs the SET2DIL (Single-Ended to Differential Insertion Loss) algorithm for validating high-speed differential transmission-line performance on PCBs. The R&S ZNB network analyzer’s enhanced time-domain capabilities, coupled with the IPC-TM-650 approved SET2DIL methodology,² enable post-processing of the network analyzer’s time-domain reflectometer (TDR) and time-domain transmission (TDT) data to display differential insertion losses on PCB traces.

The SET2DIL algorithm is a method for performing a SDD21 (differential insertion loss) four-port frequency-domain measurement using a two-port time-domain measurement. This methodology derives SDD21 using only single-ended TDR/TDT (or two-port VNA) measurements at a single probe location. Rohde & Schwarz reported that this method, in conjunction with the R&S ZNB network analyzer, eventually will replace current four-port measurements of two probe locations, which are appropriate for a laboratory environment. This technique allows easier measurement of SDD21, making it acceptable for a wider variety of users, including high-volume manufacturing, the company said.

Instruments at OFC/NFOEC

The Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC) in March provided another venue for companies to highlight communications test. Agilent, for example, demonstrated a 32-Gb/s bit error ratio tester with four-tap de-emphasis.

The company reported that as a new era of data-center infrastructure emerges to enable cloud computing, big data and analysis are driving the development of new high-speed data transfer standards such as 100-Gb/s Ethernet and 32-Gb/s Fibre Channel. The higher speeds generate new testing challenges for designers of servers, network interface cards, backplanes, and communications ICs.

Figure 2. N4960A Serial BERT with Pattern Generator and Error Detector
Courtesy of Agilent Technologies

To address the issue, Agilent has created remotely mountable pattern-generator heads for use with its N4960A BERTs (Figure 2). The new pattern-generator heads feature integrated four-tap de-emphasis (one pre-cursor, two post-cursors) operating up to 32 Gb/s, which provides designers with the signal compensation required for transmitter emulation when they characterize receivers and systems.

As part of the N4960A BERT family, the new pattern generators are configured as remote heads connected to the BERT controller with a 1-m control cable. This configuration allows the pattern generator to be located close to the device under test, minimizing the length of the signal cable, which helps minimize signal degradation.

Agilent also chose OFC/NFOEC to introduce the 86122C multiwavelength meter as well as the N7747A and N7748A optical power meters. The two-channel N7747A and four-channel N7748A bring the sensitivity of the 81634B sensor module to the compact multichannel N77 platform, with updated memory size and data-transfer speed. The N7747A and N7748A enable engineers to make parallel multiport measurements and monitor weak signals and small signal changes with high precision in, for example, communications or sensing applications. The meters can detect power levels down to -110 dBm and log data at intervals down to 25 µs with up to 1 million points per channel. An equally large data buffer supports simultaneous measurement and data transfer.

Up to eight power-meter channels fit in a single 19-inch rack. Each channel also has a front-panel BNC connector that delivers analog output voltage proportional to the measured signal. Like the faster N7744A and N7745A, these new power meters can be used with N77xx viewer software for simple control and reading and are programmable with the same set of SPCI commands as the rest of Agilent’s optical power-meter portfolio.

The new Agilent 86122C multiwavelength meter’s wavelength range of 1,270 to 1,650 nm covers all fiber-to-the-home, metro, and long-haul transmission systems. The meter can measure the spectra of up to 1,000 laser lines at once, which is sufficient for fully populated dense-wavelength-division multiplexed systems.

Field Service

OFC/NFOEC exhibits extended to field installation and service. EXFO, for example, highlighted its FTB-88100NGE Power Blazer Multiservice Test Module, introduced in February, which addresses 40G/100G field deployments.

According to Étienne Gagnon, vice president of EXFO’s Test and Measurement Division, the FTB-88100NGE Power Blazer is the industry’s smallest field-testing instrument supporting 10M to 100G rates in a single module. It covers a range of technologies including SONET/SDH, OTN, and Ethernet. Further, the FTB-88100NGE Power Blazer addresses 40G/100G field upgrades and lower-rate client service turn-ups.

Speaking at the February product introduction, Gagnon said carriers face multiple challenges as they support both legacy and packet-based services up to 100G on the same network and meet service-level-agreement requirements for each of these services. Carriers are pressured to reduce the cost per transported bit while minimizing equipment costs, truck rolls, and technician dispatches. Furthermore, 40G/100G technology is complex: new pluggable optics still are in their nascent stage, in short supply, and expensive. In addition, carriers still are looking to reduce time-to-service without compromising quality.

Gagnon said EXFO’s FTB-88100NGE Power Blazer is future-proof—the module can adapt to future requirements up to 100G, and users can immediately leverage its FLEX configuration to enable any testing capabilities to match their current needs. Additional rates and interfaces can be enabled with a software key in the field, providing maximum flexibility with minimum downtime and eliminating the need for multiple test units.

“Over the past few years, EXFO has been a leading provider of 40G/100G testing solutions. Now, as the market is moving toward 40G/100G mass deployments, we are excited and proud to launch the first truly portable field multiservice 100G test instrument at a time when carriers are coping with emerging requirements,” Gagnon said. “We realize the pressure and challenges our customers are facing to deploy this very complex technology in the field, and we are committed to offering them broad, simple, scalable, and cost-effective 10M to 100G test solutions.”

Mobile World Congress

The Mobile World Congress 2013 in Barcelona offered yet another venue for data-communications demonstrations. For example, the University of New Hampshire Interoperability Laboratory (UNH-IOL) demonstrated its MIPI testing services for mobile device component suppliers. The UNH-IOL and Agilent co-hosted the MIPI Test Corner, a section of the MIPI Alliance booth at the MWC.

Reporting from the show floor, Andy Baldman, senior technical staff member at the UNH-IOL, said booth visitors participated in demonstrations of the rigorous conformance testing performed on the mobile-device components that implement MIPI specifications. The demonstrations at MWC focused on D-PHY, the current standard for physical-layer signaling in camera and display interface applications.

At the show, Baldman, who also serves as vice chair of the MIPI Alliance’s PHY Working Group and co-chair of the Conformance Test Specification Subgroup within the MIPI Alliance, used an Agilent Infiniium MSO9404A oscilloscope to perform testing on mobile components, including ones based on Synopsys’ DesignWare MIPI D-PHY IP solution. Combined with the UNH-IOL’s custom D-PHY GUI software, the Agilent platform can capture and analyze D-PHY signaling in accordance with the UNH-IOL D-PHY Transmitter Physical Layer Conformance Test Suite.

The goal of the collaboration among the MIPI Alliance, UNH-IOL, and test-and-measurement equipment suppliers such as Agilent is to facilitate the production of low-cost mobile devices, including smartphones, tablets, and ultrabooks that offer improved performance, higher resolution images, and superior video quality.

Baldman said the next steps with regard to the MIPI Alliance will center on the M-PHY. Both D-PHY and M-PHY support data transmissions over 30 cm of PCB trace or microcoax. D-PHY offers per-lane speeds from <10 to >80 Mb/s; M-PHY extends that up to 6 Gb/s per lane. Baldman noted that M-PHY also is supported in PCIe and USB implementations.

For its part, in addition to supporting the UNH-IOL demonstration, Agilent highlighted its new protocol testing solution for MIPI Alliance Gear2 DigRf v4 RFICs. The Agilent M9252A DigRF host adapter allows developers to speed testing and analysis of RFICs used in cellular phones, tablets, and other mobile devices. At the MWC, the Agilent M9252A DigRF host adapter was featured in demonstrations hosted by Ericsson.

Ethernet and NRZ Decoding

In other news, Teledyne LeCroy announced in March an Ethernet decode software option and Manchester and non-return-to-zero (NRZ) configurable protocol decoders for its oscilloscopes.

The Ethernet decode software option is compatible with LeCroy’s range of oscilloscopes featuring bandwidths from 200 MHz to 65 GHz. With the software, users can decode 100BASE-T and 10BASE-T Ethernet signals to examine each frame within a given packet, assuring precompliance with IEEE standards. The Ethernet decode software also aids in debugging issues that are not easily solved with a protocol analyzer, such as interoperability issues, uncertain error causes, and physical-layer issues.

The Ethernet decode software processes physical-layer waveform captures to display a color-coded overlay with easy-to-understand details on the stream’s data-link layer. Decoded link-layer information expands or contracts as the user adjusts the oscilloscope’s time base or zooms in on the waveform, displaying more data with close-in views or less when looking at the big picture.

Search capabilities allow users to search for frame types, source/destination addresses, data strings, and other attributes. A user can locate source or destination addresses from one frame and search the waveform for other packets with matching addresses. The search tool provides a list of the most common error conditions such as missed start of frame and missed terminate frame.

The company also announced Manchester and NRZ configurable protocol decoders for its oscilloscopes (Figure 3). The decoders enable users to specify a range of physical-layer characteristics for Manchester or NRZ encoded signals. They define the grouping of bits into words and words into frames, which facilitates analysis of custom protocols based on those generic encoding schemes. Decoded information then is shown in a color-coded overlay directly on top of the physical layer waveform.

Figure 3. Manchester and NRZ Configurable Protocol Decoders for Oscilloscope Platforms
Courtesy of Teledyne LeCroy

The company noted that many of today’s data-communications protocols are built on Manchester or NRZ encoding—for example, specialized buses such as Digital Addressable Lighting Interface for control of building lighting and the Peripheral Sensor Interface 5 used to connect sensors to controllers in automotive applications as well as proprietary, custom buses. In all of these cases, basic Manchester and NRZ schemes are modified to create the more complex, specialized protocols.

With the Manchester and NRZ protocol decoders, users may specify bit rates from 10 b/s to 10 Gb/s. Idle states, sync bits, and header and footer information can all be configured to decode custom preambles or CRC details. Decoded information is displayed with a color-coded overlay, which expands or contracts as the user adjusts the oscilloscope time base or zooms in on the waveform. Users can quickly search long captures of decoded Manchester and NRZ waveforms for specific bus details. Decoded data is displayed in an interactive table. Clicking on any line in the table opens a zoomed view of that instance in the waveform.

Conclusion

Vendors are continuing to develop their data-communications test capabilities. Agilent, for example, in April introduced three optional trigger/decode packages for its 2000 X-Series oscilloscopes: DSOX2EMBD for embedded designers supports RS-232/UART interfaces, DSOX2COMP handles I²C plus SPI for component-level communications, and DSOX2AUTO deals with CAN plus LIN for automotive applications (Figure 4). Mike Hoffman, product marketing engineer for high-volume oscilloscopes at Agilent, said these packages running on the Agilent scopes offer decoding speeds faster than available on other instruments that perform the decoding using a software-based post-processing technique. The X-Series oscilloscopes, he said, make use of an ASIC.

Figure 4. InfiniiVision X-Series Oscilloscope with CAN/LIN Protocol Analysis
Courtesy of Agilent Technologies

In addition, Agilent has introduced software for decoding MIPI Radio-Frequency Front-End (RFFE) protocol packets on Infiniium 9000 oscilloscopes. The new protocol decoder provides design and validation engineers with a way to validate and debug their RFFE interfaces. RFFE is a specification that offers a common method for controlling RF front-end devices, namely power amplifiers, switches, power-management modules, antenna tuners, and sensors. RFFE provides point-to-multipoint connectivity for control of the RF front end and is able to scale to dozens of slave devices, which are connected to a single master device.

Compliance testing support for Energy-Efficient Ethernet (EEE) standards used in networking applications also has been developed for Infiniium Series oscilloscopes. Agilent’s solution for transmitter tests includes 10BASE-T, 100BASE-T, and 1000BASE-T EEE test standards as described in the IEEE 802.3az-2010 specification.

Agilent also introduced compliance testing support for MOST (Media-Oriented Systems Transport) and BroadR-Reach standards used in emerging automotive applications. The solution covers all equipment needed for physical-layer testing, including oscilloscopes, spectrum analyzers, and pulse/function generators.

For its part, Tektronix has announced an M-PHY test solution for Synopsys silicon-proven HS-Gear3 IP, a key part of the MIPI Alliance M-PHY physical-layer specification for mobile devices. The Tektronix test solution allows you to characterize designs and verify performance, ensure compliance with M-PHY specifications, or quickly isolate problems. Silicon-proven IP helps semiconductor vendors adopt new standards based on M-PHY.

Such innovations will continue as instrument vendors help their customers contend with an every widening array of data-communications standards and exploding data rates.

References

Nelson, R., “Serial Bus Test: From EDA to TDR, Tools Support High-Speed Analysis,” EE-Evaluation Engineering, January 2013, p. 18.
IPC-TM-650 Test Methods Manual, IPC-Association Connecting Electronics Industries, October 2000.