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WLAN Access Point/Modem Manufacturing Test Bench

Objective


To develop a fully integrated test bench capable of performing RF transmitter, receiver and board level tests for validating WLAN access points in the production line.

Client requirements & challenges faced


Given production line requirements and dynamics, SeaSolve’s traditional test bench methodology had to be changed drastically to accommodate the following requirements:

  • Automation of RF tests
  • Maintaining high device production throughout shop floor times
  • Completely test any device in under 40 seconds (RF tests)
  • Minimize radio interference at each test bench

Specifications of the tools used


SeaSolve’s software developed for this application was integrated with the National Instruments (NI) RF PXI platform.

  • LabVIEW Graphical Development Environment (for main software program)
  • National Instruments PXI vector RF signal generator(s) and analyzer(s)
  • National Instruments PXI RF switch(es)
  • National Instruments PXI digital multimeter
  • Willtek RF shield(s)
  • Device under test – WLAN ADSL Type 2 modem + access point (LAN interface)

Solution overview


SeaSolve’s WLAN automated compliance tester for the manufacturing line combines WLAN signal generation, signal analysis and compliance testing solutions into one concise package. It offers great accuracy and speed and integrates with the National Instruments’ RF test equipment. Furthermore, the solution is able to control the WLAN device-under-test in order to achieve test automation.

Automated Manufacturing Tests

Above Figure shows Main screen of controller software

Key approaches to challenges

1.

Automation of RF tests

  Leveraging past experience in automated compliance testing, SeaSolve was able to communicate with the device-under-test (DUT) through the TCP/IP interface. Commands sent through SeaSolve’s application software to the device enabled it to either transmit or receive packets continuously. These ‘test modes’ were used to control the DUT through the software itself while running transmitter and receiver tests sequentially. This form of test automation (for the RF tests) eliminates the need for manual operator intervention during the tests, which not only saves cost but also time.

2.

Maintaining high device throughput/production

  Combining test automation with fast test times, the SeaSolve/NI test bench has been able to reliably test up to thousands of devices per day. This is further discussed in the section below.

3.

Completely test any device in under 40 seconds (RF tests)

  SeaSolve’s test APIs that were employed in the main software program have extremely quick algorithms that enable measurements to be taken in several milliseconds. This, combined with the fast hardware response of the NI PXI platform, made it possible to test any given DUT in between 25-40 seconds, depending on the settings chosen by the operator(s).

4.

Minimize radio interference at each test bench

  RF shielded boxes, designed specifically for production line testing, were used to house the DUT and RF interface.

Methodology and features


The main features of SeaSolve’s WLAN Tester are:

1.

Fast Test times

  The WLAN Test Solution is designed to minimize measurement times, thereby reducing the overall test time. The tests usually take around 30-40 sec to perform both the Transmitter and Receiver measurements.

The Transmitter tests include the following measurements:
 
Arrow Error Vector Magnitude (EVM)
Arrow Closed Loop Power (CLP)
Arrow Power Spectrum Density (PSD)
Arrow Occupied BW
Arrow Center Frequency Offset (CFO)
  The Receiver tests include the following measurements
 
Arrow Packet Error Rate (PER)
Arrow Bit Error Rate (BER)
Arrow Max. Input Power
  Usually, the test times may also be affected by an additional operator handling time of 5-6secs per DUT.

The solution relies on booting and testing a number of DUTs simultaneously using RF switches. The boot-up time could be anywhere around 40secs, although this is vendor specific.

2.

Multiple device testing by Switch

  Multiple devices can be tested simultaneously by splitting the Transmitter and Receiver tests across DUTs. In this case, an RF switch is used to switch RF test signals from one DUT to another. This is a big boon to WLAN manufacturing testing as it reduces test time drastically.

The main reason for multiple device testing is that it helps to save device boot-up time. For instance, if we are testing 4 DUTs at the same time connecting through an RF switch, we don’t have to wait to boot each DUT, and therefore this method saves a lot of time. We just wait for at least 40 sec for the first boot-up to take place after switching on the entire system and can then directly switch test signals to any of the 4 DUTS connected to the RF switch/MUX.

3.

Report Integration

  The WLAN tester saves reports in html format for future reference. On the other hand, production floors can save this data in their database. This can be used for later reference in case there is a failure of a particular DUT or batch of devices.

4.

Device Throughput

  The WLAN Tester, with its fast and efficient test times, enables higher device throughput on the production shop floor.

For example, one test bench with the NI/SeaSolve solution can test up to 4 DUTS in 3 mins. That is 80 DUTS in one hour. On the shop floor, there are usually 3 shifts a day, each consisting of 8 hours of testing. So that makes it 1920 (640*3) DUTs a day per test bench.

5.

Flexibility in Hardware and Software

  Configure Rx sensitivityFigure shows the Sample test configuration – Rx sensitivity

SeaSolve is open to any customization needed in the hardware as well as software used in the test bench.

In hardware, for example, the National Instruments’ platform allows for the addition of other hardware modules to the test bench. Extra spaces in the test bench chassis may be used for a DMM (Digital Multimeter) to carry out board-level measurements.

In software, if a client needs a particular test to be included (or excluded), we can customize the test flow accordingly. In order to achieve DUT control, it may also be necessary to program the test solution to control the devices through TCP/IP or RS-232.

6.

Miscellaneous Features

 
Arrow Reduces investment costs to a great extent
Arrow Operator friendly
Arrow Provides very good device throughput
Arrow Results are reliable and repeatable, given regular test bench calibration
Arrow Customization of test bench software and hardware available
Arrow The same RF test hardware can be used for different wireless standards (not just WLAN).
The platform supports testing up to 6.6 GHz
Arrow Highly versatile and can be utilized in the design and/or production processes
Arrow High modulation accuracy
Arrow Verification of chipset/reference/prototype designs
Arrow Elegant and easy to use
Arrow Supports offline analysis (of signal data)

The power of SeaSolve’s WLAN Tester helps save time, money, and reduces associated development risks.

SeaSolve’s solutions’ seamless integration with the National Instruments PXI-based RF modules requires minimal hardware knowledge and interaction on the user’s part. The NI platform also enables testing of a DUT at any stage of development, rather than having the designer wait to test a finished product. Therefore, the SeaSolve/NI test-bench is very useful for production testing of wireless devices as well as during the design validation phase. The test bench can be further extended to support next-generation technology testing as well.