Production Test System for a High-Bandwidth Optical Network Switch

Author(s):
Sorin Grama - CAl-Bay Systems

Industry:
Telecommunications

Products:
PXI/CompactPCI, TestStand, LabVIEW

The Challenge:
Creating an automated test system for a telecom switch matrix to dramatically decrease testing time and increase efficiency. instrument.

The Solution:
Using NI PXI hardware with NI TestStand and LabVIEW software to develop a turnkey system that automates testing of a telecom switch matrix and reduces test time from a few days to a few hours.

Introduction
A telecom switch performs the basic function of routing incoming signals or phone calls from one place to another. It is a critical component that sits at the heart of any local phone exchange. TeraBurst Networks, an emerging Silicon Valley company that provides high-bandwidth switching solutions for next-generation optical networks, created a wavelength-level switching system based on an innovative RF and microwave frequency technology.

Cal-Bay Systems, Inc., in conjunction with TeraBurst Networks, developed aturnkey production test system to test the RF performance of an NxN switch matrix. This flexible system proved to be as valuable for design verification as it was for production testing.

Creating a Productive, Cost-Effective System
TeraBurst Networks needed a complete turnkey system that automated a tedious manual testing process for the switch matrix component of their optical network switch solution and to test the RF performance of a signal path by measuring critical electrical parameters using a high-bandwidth vector network analyzer instrument. We needed to develop automated software to control the switch matrix and instruct it to switch from one path to the next, acquire the measurements from the network analyzer, and print a summary report of the paths that failed the design requirements for signal integrity.

Additionally, we needed to design an RF test fixture for inserting the device under test (DUT). This was a complex task because the fixture had to handle signals of very high frequency without introducing an distortions of its own. We also had to develop a complementary RF multiplexer to communicate with the switch matrix and route the input and output signals from the network analyzer. We needed to integrate and build this system and deliver it as one complete solution.

We based our software solution on NI TestStand and LabVIEW. TestStand was the obvious choice for this production test system because it enabled us to build a test sequence that was both powerful and flexible. We used the built-in operator interface, the report generation module, and limit checking modules in TestStand rather than developing our own. Because of this, we could concentrate on developing the test modules rather than the low-level details. Using TestStand test management software was critical in helping us build and deliver the system on time and within budget.

For the hardware, we used the PXI platform for its compact size and reliability. Reliability is critical because production test system must run with very little down time. The compact size is important for contract manufacturers who use many testers on a production floor. In addition, we could easily integrate the PXI hardware platform into our test rack.

We used a GPIB interface to communicate with a network analyzer and a PXI-6533 as a high-speed, bi-directional digital I/O interface to communicate with the device under test. A PXI-6533 card has a tri-state feature, which allows for bidirectional communication on the same port. A communication interface to the device under test was an 8-bit parallel interface with handshaking lines. With this interface, a controller commands the switch to connect the different paths.

We developed 64x1 RF multiplexers as separate instruments. An RF multiplexer is a set of specialized electro-mechanical relays that operate at high frequencies and route many input signals into one output signal or vice-versa. To operate the relays, we used the FieldPoint DO-401 modules. We were able to seamlessly integrate the modules in a separate enclosure and control them via serial port like a standard instrument. We found that we could use these RF multiplexers in other projects where multiple signals are routed to one instrument.

To test the device, we developed an RF test fixture. With the test fixture, an operator can simply insert the device under test in a drawer. When the drawer is closed, TeraBurst’s proprietary connection system engages and connects the system to power the device and to link it to a high-bandwidth backplane that routes the signals to the network analyzer via the RF multiplexers. The fixture, the hardware, and the network analyzer all fit in a standard 19 inch rack.

Dramatically Reducing Test Time
Close cooperation between Cal-Bay and TeraBurst Networks ensured that we delivered quality systems on time. In the end, we delivered several similar systems to test the switch matrix and one system tests the individual switching cards that make up a switch matrix. In the case of the switch matrix tester, we reduced the test time from days to just under a few hours. The systems proved to be invaluable tools for design engineers and test engineers alike.

For more information, contact:

Sorin Grama

Cal-Bay Systems, Inc.

3070 Kerner Blvd. Suite B

San Rafael, CA 94901

Tel: (415) 258-9400

Fax: (415) 258-9288

E-mail: sgrama@calbay.com

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