Environment and Features for a Cable Test System
There are many aspects to producing a cable such as those used in HDMI, DisplayPort, USB and Infiniband. Among the many steps are copper extrusions, insulation of conductors, adding the outer protective coating for the bulk cable and then the final steps of adding the connectors and sealing the cable ends. The final step of adding the connector begins with terminating the individual wires on the connector. This process is primarily completed manually today and this defines the kinds of environments where final cable test takes place.
These environments are large warehouse structures with large numbers of assembly workers and do require the test device to be electrically and mechanically robust. The large numbers of assembly workers produce cables at rates of one every few seconds and these have to be tested and approved in this time to maintain the throughput. Another key feature of the test device is to be able to track the defects that occur — this ultimately allows the Process Engineers take appropriate actions to remedy the cause of the defects.
In fact Process Engineers want to be able to analyze the production run data at the end of a day or a shift so the test device should allow easy access to data. The ideal solution for them is a cable tester which integrates itself into the IT infrastructure of the production plant and stores results to a database for easy post processing.
Built in Cable Test
For the semiconductor microchip the idea of Built In Self Test (BIST) is well accepted. So in addition to the circuitry for normal tasks performed by a particular microchip, it will also include blocks of circuitry to ensure that the microchip’s normal task blocks are functional. This basic idea has been employed in a new generation of active cables where circuitry has been added to the cable to check the finished performance of the cable. As well as providing a final statement of the quality of the cable the BIST function in these cables can be used to find the optimum equalisation setting for a particular channel in a particular cable. This ability greatly influences the end quality of the cable.
To test the high-speed data channels on a cable, a data generator and some kind of measurement equipment are needed. The BIST function in an active cable does both functions. The BIST block generate data at the sink end of the device and passes it through the source end of the cable, through a connecting card called the “Plug-in Sacrificial Card” to the source end of the cable. From here it passes through the cable to itself and back to the sink side. At the sink side it is now measured, and the damage done by the cable configured in a loop can be assessed.
Figure 6: Active Cable Tester
Because this is a dedicated measurement system there are techniques to accelerate the measurement without compromising accuracy. Dedicated silicon solutions aren’t slowed down with huge software overheads or slow mechanical parts. The system shown in Figure 6 has the ability of testing the high-speed channels of an active cable in less than 5 seconds. As well as doing measurements, the system is easily coupled to a PC system to store the results to a database for later analysis. The system is also easily enhanced to provide visual indicators, which are useful for the production environments to flag passing/failing cables or any other production related issues.
Conclusion
A new breed of active cable is enabling higher performing portable cables. With this evolution there is a corresponding requirement for 100% in-production cable testing. Continuity testers, oscilloscopes, and BER testers all prove inadequate, but a new cable BIST methodology can satisfy all requirements. Along with the basic test requirements the system linked to standard IT systems to allow easy access to production data can greatly improve process control, and as a result, the price of guaranteed quality.
About the authors:
David Guthrie is a Principal Engineer at RedMere based in Cork, Ireland. He is responsible for the development and management of active cable testers for multi gigabit serial communication applications. He can be reached at david.guthrie@redmere.com .
Dr. John Horan is Chief Technology Officer at RedMere, based in Cork, Ireland, and is responsible for the technology development for RedMere’s high-speed communications channel products. He can be reached at john.horan@redmere.com
