Testing, testing for design and manufacture
14 May 2008
Electronic complexity and decreasing product development cycles mean that designers are relying on test equipment at the design verification and manufacturing test stages
The world of test and measurement has gone full circle as modular, reconfigurable test systems are back in fashion. The fast moving communications market is the primary driver of this trend. Undoubtedly, communications is the largest and fastest growing electronics market, embracing wired and wireless, voice, and data systems. Each of these domains has dozens of standards in various stages of adoption, making it one of the most complex markets.
Emerging standards sometimes remain fluid for years despite, or perhaps due to, the pace of technology change. The trend today is towards multi-standard systems, such as combined fixed/mobile network services. The challenges facing the test and verification of these system components are not to be taken lightly.
Over the last 10 years in the telecommunications sector, PDH has been overtaken by SDH and SONET. Transmission speeds have risen dramatically from 144Mbit/sec and 565Mbit/sec, to 2.4Gbit/sec, 10Gbit/sec, and more recently nearing 40Gbit/sec.
The broadcast industry is in the throes of a major change. The switch to digital transmission generated new standards and a corresponding demand for new test systems. Mobile TV is an emerging market and represents the latest battleground for competing international industry standards. Manufacturers need to keep their options open and respond rapidly to market demand. Equally, test equipment must follow suit. When wireless communication protocols, ZigBee and Bluetooth, wireless LANs and WiMAX are considered, as well as mobile telecommunications such as GSM, LTE and 4G, it is clear that these examples only scratch the surface.
Reliance on test and verification
Meanwhile, there is enormous pressure on designers to swiftly develop new products and for service providers to deploy them. Poor quality, uncorrected design errors, late market entry, or incompatibility with standards can result in an irretrievable loss of market share and a severely damaged reputation. With increasing electronic complexity and shrinking product development cycles, designers are relying heavily on test equipment at the design verification and manufacturing test stages. Uncertainty of standards and markets requires flexible and responsive test solutions.
Product development teams not only have to test their new designs against a standards-based specification, but also ensure that the finished device has been manufactured correctly. Test engineers are required to check the functionality of the products, conformance to standards, and interoperability with other system and subsystem components. Developing and maintaining test systems for an industry that is in a constant state of flux is becoming a complex, time consuming, and expensive business.
Credit must be given to the major players in the test and measurement world for responding quickly to the needs of the industry; especially when a standard is ratified and set to become widely adopted. Dedicated test sets are efficient and cost effective for equipment in volume production, but when the standard or the technology is superseded, the test equipment has to be upgraded or replaced. Although many dedicated test sets are designed to be software upgradeable, there are limits and investment in new equipment is ultimately the only solution.
Easy to configure
A modular and reconfigurable test system is increasingly becoming the preferred solution, especially when standards-specific test sets are not yet available, or too expensive to make an early commitment. By selecting the most basic, individual items of test equipment, it is surprisingly easy to configure an application-specific, yet reconfigurable test system.
There are a number of fundamental instrumentation building blocks, including RF signal generators, signal analysers, arbitrary waveform generators, function generators, spectrum analysers, oscilloscopes, counter timers, and power analysers. Instruments are available from a multitude of manufacturers and vary in terms of features, functionality and price. This allows a test department to build a system for highly specific or general, broad-based requirements.
These instruments can generally be integrated using industry standard interfaces, and data is easily exchanged between them. A number of widely used scripting programmes and test generation software packages are available, making use of standard APIs (application programming interfaces) and often hosted on a standard PC. Suitable for development, prototyping and production test applications, custom test routines can usually be developed swiftly. Many instruments provide some automatic test generation features and most enable standard tests to be automated, either on a stand-alone basis or as part of a larger system.
These application-specific test systems can be built early in the development phase; generally before a dedicated test set might become available. They can be reconfigured easily and rapidly as standards or project requirements evolve. Overall cost can be considerably less than dedicated test sets which are notoriously expensive. In addition, individual instruments can be re-used at a later date for installation and maintenance, or even for another project.
The trade-off is that engineering effort needs to be expended in designing and implementing the complete test system and developing test software. Researching and selecting the best instruments for an application can be time-consuming and sourcing them from a number of different vendors can be fraught with problems, too. Furthermore, test engineers are in short supply. Cutbacks in engineering support roles such as test come at a time when one of the most critical design challenges has been identified as verification. Recruiting and retaining test engineers with the knowledge and experience of test methodology and programming can be difficult.
Expert advice
Aspen Electronics supplies a range of RF and microwave test and measurement equipment, as well as general purpose instrumentation sourced from global manufacturers. More than 20 years of trading has resulted in knowledge of the test and measurement industry; particularly for RF and microwave instrumentation, serving the wired and wireless telecommunications, satellite communications, broadcast, fibre optics, avionics and general instrumentation sectors.
A knowledgeable team of experts provides advice on the range of equipment available from a host of worldwide vendors. In-house experts can offer guidance on test system configuration, based on their knowledge of various specialist applications. Well-equipped test and demonstration laboratories are available, as are calibration and service facilities. Furthermore, experts often have fast-track access to manufacturers for technical data, requests for custom options, specialist plug-ins, and information on lead times and delivery.
However, communications is certainly not the only industry sector that takes advantage of the modular and configurable approach to test system development. The military, avionics, space and medical industries are all heavily reliant on RF and microwave technology and have found major benefits. In addition, the automotive industry is experiencing the predicted expansion of incar networking, car-to-car, and car-toinfrastructure telemetry, so it is fast predicted to be next.
Configurable test sets
The following examples are presented in increasing order of technical complexity and clearly demonstrate the scope and versatility of the modular, configurable approach to test.
Power Supply Testing
A configurable test system for either AC/DC or DC/DC power supply designs typically comprises of an AC or DC programmable power supply (essential for simulating a range of input voltages and conditions), a programmable electronic load to provide a variety of load conditions, and an oscilloscope (figure 1).
In this case, the oscilloscope is the key measurement tool. A strong performer in this application is the Le Croy WaveJet or WaveSurfer. With suitable voltage and current probes, typical measurement parameters include gate drive characteristics, inrush current, instantaneous power, SOA (safe operating area), modulation analysis, and line power analysis.
At the heart of any test system for RF (wireless) communications oriented applications is signal or waveform generation. Various types of instrument are available, including general purpose signal generators and instruments targeted at a particular application and/or a set of standards. It is quite possible to combine different instruments to extend the capability of a test system.
In the first example (figure 2A), the Tabor WW2572A Arbitrary Waveform Generator is used in conjunction with a Credix DSG3000 RF Vector Signal Generator. This combination will produce RF signals up to 3GHz with modulations including AM, FM, FSK. PSK and n(QAM) up to 256QAM.
For applications beyond 3GHz, the Tabor AWG can be combined with another general purpose signal generator (figure 2B). Depending upon the choice of RF generator, it is feasible to produce an RF signal with complex modulation up to a carrier frequency of 6GHz and beyond.
Duo-binary modulation
For highly specialised applications, it is often possible to construct a custom test set-up from readily available components; thus creating a dedicated test system that might otherwise be difficult to source elsewhere. For example, Duo-binary modulation is a relatively new idea applicable to very highspeed optical transmission systems. It gives system designers certain advantages over traditional NRZ modulation schemes.
HOWARD VENNING is managing director, Aspen Electronics.
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