Fixtures, instruments augment high-speed digital test

EE-Evaluation Engineering’s January 2016 print special report on high-speed digital test commented on instruments including oscilloscopes, BERTs, vector network analyzers, and protocol analyzers as well as software.

Several industry experts elaborated on high-speed digital test. For example, the print special report outlined the functionality of the Anritsu MP1800A BERT Serial Quality Analyzer to meet high-speed signal integrity testing requirements. Hiroshi Goto, Anritsu business development manager, elaborated on jitter measurement. “Anritsu has also developed a 56G/64-Gb/s jitter tolerance measurement solution that incorporates the MP1800A, as well as the MUX MP1861A and DEMUX MP1862A,” he said. “Linking the MP1861A and MP1862A with the MP1800A, which features a built-in pulse pattern generator (PPG), error detector (ED), and jitter modulation source, supports generation of serial NRZ data, as well as BER and jitter tolerance measurements at bit rates up to 64.2 Gb/s.”

Anristu has also enhanced the MP1800A to serve as a 64G NRZ and PAM-4 test solution supporting JOTL (Jitter tolerance test) and BER measurements. “Combining the MZ1834A 4PAM converter with the 28/32 Gb/s PPG supports generation of 4PAM data signals,” Goto said. “The BER of the three eye patterns of a 4PAM data signal can be measured simultaneously by combining a power divider and power splitter with the MP1800A high-sensitivity ED. Additionally, the true BER of 4PAM signals can be measured using both the MP1800A long-memory programmable pattern function and the error mask function for removing unwanted errors.”

Anritsu also supports simultaneous BER measurements and eye-pattern analyses with the recently introduced the BERTWave MP2100B. “The internal BERT function supports BER measurements at speeds ranging from 125 Mb/s to 12.5 Gb/s, as well as eye mask and eye pattern measurements,” Goto said. “The built-in sampling oscilloscope has a bandwidth of typically 25 GHz for electrical interfaces and a bandwidth of typically 9 GHz for optical interfaces. In addition, up to six optional Bessel filters can be built-in for measuring optical signals using the oscilloscope.”

Fixturing is an important issue when it comes to high-speed test. Tami Pippert, high-speed digital industry marketing program manager at Keysight Technologies, said, “Solving issues related to fixturing and probing comes from designing them in as part of the total solution—regardless of where [those issues appear] in the work flow.”

As an example, she said, “Our ADS simulation software provides tools to accurately model fixtures and probes, so that their effects can be incorporated and ensure correlation between simulations and measurements.” In addition, she said, “To support Type-C development, we recently introduced a new fixture that solves numerous issues with the new connector including the flip.”

Furthermore, Keysight addresses automatic fixture removal with tis Physical Layer Test System (PLTS) software, which, Pippert said, “…enables accurate and precise fixture removal with an intuitive interface for the high speed digital designer.” Through-reflect-line (TRL) and other traditional methods require the painstaking design and fabrication of multiple line calibration standards, she said, adding, “Now, with 1-port AFR, the engineer simply disconnects the fixture from the DUT to provide PLTS with a high-quality open reflect standard. The new reference plane created by the open circuit at the fixture output allows precise de-embedding of the fixture.”

With respect to probing, Pippert said, “An area of ongoing focus and development for us is the fact that many high-speed digital bus sizes are becoming smaller and smaller, making it difficult to keep the probes usable. An example of our solutions in this space include the W4640A DDR4 BGA interposers with zero insertion force (ZIF) probe/cables, and Soft Touch Pro connectorless probe cables that enable engineers to validate and debug simultaneous read and write DDR4 or LPDDR4 traffic.”

National Instruments addresses high-speed digital test with instruments such as the PXIe-6591R and PXIe-6592R, which include user-programmable FPGAs, as described in our January print special report. Chris Nunn, product engineer for modular instruments at NI, elaborated on such instruments, saying, “Because of the flexibility provided by software-designed instruments, we can release new IP and toolkits that customers can use with just a software update. Our current process for identifying the protocols to go after involves a mixture of our team keeping a pulse on the industry and working closely with customers. Future candidates involve reference designs for JESD, Serial RapidIO, and 10GbE. These reference designs include both HDL and LabVIEW code to compile serial interfaces that work out of the box.”

Nunn noted that the PXIe-6591R and PXIe-6592R provide a protocol-aware test solution for custom high-speed serial interfaces. “The user-programmable FPGA and openness of our PXIe-6591R and PXIe-6592R allow engineers to integrate their custom IP into the test instrument to test their custom interfaces,” he said. “Furthermore, many customers have benefited from the flexibility of the instrument to interface to different high-speed serial interfaces by simply flashing a new bitfile.  This enables a single instrument to test different serial interfaces on the same or different DUTs, allowing for flexible and scalable test systems.”

He added that he PXIe-6591R and PXIe-6592R both use industry-standard connectors to simplify fixturing and probing issues, including include mini-SAS HD connectors on the PXIe-6591R model and SFP+ connectors on the PXIe-6592R model, as well as a mini-SAS HD to SMA breakout for increased flexibility. “Many custom mass interconnect solutions are available through partners from The NI Alliance Partner Network such as Virginia Panel Co.,” he said.

High-speed digital communications systems designers are looking at complex measurement schemes such as PAM-4. Patrick Connally, technical marketing engineer for high bandwidth oscilloscopes at Teledyne LeCroy, said, “PAM-4 uses a four-level signaling technique to encode two bits of information per symbol rather than one bit as encoded in a traditional NRZ signal. The doubling of data transfer rate comes at a price, though, in the form of increased signal complexity compared to two-level NRZ signaling. The PAM-4 eye diagram comprises three eye openings instead of one and includes 12 types of transitions. Engineers must understand how their transmitters, channels, and links affect PAM-4 eye quality while quantifying the degree of eye closure due to timing jitter and noise as a function of bit-error ratio (BER).”

Teledyne LeCroy now offers a PAM-4 signal-analysis tool that helps engineers meet PAM-4 challenges. “The PAM4 analysis tool decomposes total jitter and noise in a signal into its random and deterministic components, giving a full accounting of aberrant behavior,” Connally said. “In addition to quantifying jitter, noise, and eye height/width, the tool helps users understand the root causes of jitter by displaying a full complement of visualizations, including histograms, tracks, spectra, and bathtub curves.”

Connally cited several other tools Teledyne LeCroy offers for high-speed digital test:

• The QPHY-USB3.1-Tx-Rx transmit-receive package automates USB 3.1 transmitter and receiver compliance testing, characterization, and debug. As such, the comprehensive suite performs USB 3.1 testing on both Gen 1 (5 Gb/s) and Gen 2 (10 Gb/s) devices under test according to the latest USB 3.1 specification.
• The QPHY-MIPI-MPHY automated physical-layer compliance test software gives designers confidence in new MIPI M-PHY designs. The QPHY-MIPI-MPHY software performs testing on HS-MODE, PWM-MODE, and SYS-MODE signals at all currently specified GEARs. It is compliant with the MIPI Alliance’s Conformance Test Suite for MPHY.
• UNIPRObus D, a MIPI UniPro protocol decode solution, provides easy-to-use debug of UniPro interfaces. Building on Teledyne LeCroy’s existing MIPI MPHY decoding capability, UniPro Decode supports HS GEAR1, GEAR2, and GEAR3 and PWM Mode (G0-G7) signaling for comprehensive data rate coverage.