J-BERT goes modular, emulates channel

-January 21, 2014

Agilent (Keysight) Technologies has long been a manufacturer of BERTs (bit-error-ratio testers) with its benchtop J-BERT and large modular ParBERT systems. Now, the J-BERT goes to a modular format with the M8000 series High-Performance BERTs. The instrument, aimed at chip and system designers, is based on the AXIe backplane. A chassis (M8020A) can accomodate up to two BERT modules. Each module is available with one or two channels—each with a pattern generator and analyzer—and can run at data rates of 16Gbits/s or 32Gbits/s. Thus, a system can have from one to four channels. In addition, a three-slot module (M8041A) adds clock recovery.

Many of today's high-speed serial links used in datacenters, mobile devices, PCs, and tablets need BER testing that goes beyond simply counting bit errors. The M8020A and its BERT modules, while not a protocol analyzer, is aware of the link protocols that might run over the physical link under test. That's because the J-BERT needs to make a data connection to the DUT for loopback testing. Once it performs link training, the J-BERT can test transmitters and receivers.

More than a pattern generator with a BERT, the system can perform receiver stress testing by adding jitter, intersymbol interference, crosstalk, skew, and channel loss for receiver stress testing. The figure below shows how the system lets you calibrate a transmission channel at up to three points: at the transmitter, at the end of the transmission channel, and at the receiver under test. You will need a real-time oscilloscope to calibrate at locations TP2 and TP3 in the diagram. By viewing the signal at the test points, you can adjust impairments as needed.

When testing a transmitter, you often need to remove the effects of the test fixture and transmission channel to view the sys and count bit errors. Even a clean eye coming from the transmitter can be impossible to detect a bit at the far end. The M8020A J-BERT can de-embed and thus compensate for losses in the test fixture. In the figure below, a received signal on the left has no eye opening and thus the J-BERT would be unable to detect bits. Adding de-emphasis at the J-BERT opens the eye to where the analyzer can count BER.

Unlike the benchtop J-BERT, the modular version has no screen. You can operate it from a PC using a USB or Ethernet link and M8000 software—$9600 for a single license or $14,800 for a network license. The instrument also has a built-in Web server for configuration with a browser. Product manager Michael Reser explained at a prerelease demonstration of the J-BERT that the software operates like Windows 8 and is touch-screen capable. There are no virtual knobs in this user interface. In addition to using prewritten software, you can create custom automated tests using the J-BERT's programming interface. Software is also available for automating PCIe, USB, or SATA receiver testing starting at $20,000.

System prices start at $122,200 for a one-channel BERT with clock recovery.

Agilent Technologies, www.agilent.com

M8020A J-BERT product page

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