Mobile makers demand better test
13 October 2008
Maintaining competitiveness in the terminal supply market requires continuous innovation not only in the design of new features but also in driving down cost. Tim Carey looks at how a different quality assurance test paradigm is helping to lower manufacturing cost.
The adoption of intensive automation, offshore manufacturing where labour rates are lower and outsourcing to OEM are now recognised as a given for any major player in the mobile phone industry. Reducing costs still further requires more subtle approaches.
A closer examination of the cost versus benefit of quality assurance testing is an obvious target. Over time, as other costs have been reduced, product testing has become an increasingly significant proportion of the total cost. While efforts to reduce costs associated with test have been successful, they are countered by increased product complexity and time to market pressures, requiring more rather than less testing and utilisation of higher priced capital equipment. Where possible, manufacturers have adopted reduced test scenarios backed by batch sampling but this risks product quality.
The era in which quality is assured by using functional based test methodologies is rapidly coming to an end. This test methodology treats the device as a mobile phone and tests it by making and receiving phone calls during which parametric performance is measured. This approach might have been relatively efficient when terminals were just single band mobile phones but this is no longer the case. Making and receiving calls requires the test system to emulate a radio base station supporting various protocols rendering the test equipment overly complicated and hence expensive. Moreover the testing of terminal performance parameters requires the device to be placed under the control of a system-specific signalling protocol designed to be a robust communications protocol and not a high speed manufacturing process control protocol and therefore counter to the needs of manufacturing. This type of testing has served the industry well, especially as the market proliferated and manufacturers raced to gain market share and brand value. As cost leadership is now key to future success one needs to take a more informed approach to quality assurance testing.
One emerging method is to treat the device as ‘open’. A mobile phone device can be viewed as a computer to which are added a number of RF and other peripherals. The quality assurance process is no different in that its purpose is to provide assurance that no errors have occurred in the supply chain, component handling or assembly process and not a means of re-verifying the design. The difference is that by considering the device as open, a test process can be implemented that is optimised for speed. Indeed by taking this approach the test requirements of the device are an intrinsic part of the design to the point where a large measure of self testing can be accomplished.
However, designers of mobile phones must consider many factors, only one of which is design for test. Adding components that consume energy, space and cost over what is the bare minimum is hard to justify if purely for the benefit of design for test. Indeed designers are encouraged to use as few, common, lower grade components as possible. RF component tolerances compound to give rise to variations of performance sample to sample that must be compensated for by alignment procedures. RF circuit designs behave differently as frequency, level and temperature varies. Techniques for compensating for these effects varies between manufacturers but is largely influenced by the choice of chipset used. The number of measurement points required over which correction data is calculated can be very high. The time associated with calibration is then another source of cost that can be influenced by choice of test equipment and test philosophy. Suppliers of mobile terminal chipsets have recognised this and have introduced special alignment modes that accelerate test time by sequencing through a predefined number of device states automatically rather than as a series of static conditions. This approach requires test equipment that can perform synchronously. The equipment is configured in advance to mirror the change in terminal condition, e.g. as it changes transmit and receive frequency or level. This approach certainly helps to speed up the test process but can still result in test instrument hardware being relatively under utilised.
A closer examination of the manufacturing process reveals conventional non-signalling based test equipment has a one-to-one relationship with the device under test. This means that for the duration of the test process, the test resource is available only for that device. Moreover, the device is only actively using the test equipment hardware portion while acquiring a signal from the device or while stimulating the device. Between each test or while processing acquired data the hardware element is idle. Test equipment hardware is made up of a forward path providing stimulus signals for receiver alignment and verification and a reverse path for transmitter alignment and verification. In most practical cases these resources are not used simultaneously and the relative difference in complexity for Rx and Tx test generally means that hardware used for Rx is very under utilised and therefore redundant most of the time. This accounts for the poor utilisation of conventional non-signalling based test equipment. By de-coupling the one to one relationship between device under test and the test equipment and also de-coupling the relationship between the test equipment hardware transducers and their signal processing parts far greater levels of hardware utilisation can be achieved lowering the cost of test through more efficient use of capital equipment.
Aeroflex is leading the way in supplying capital equipment to serve this new paradigm. Equipment that has proven track record and has been purpose designed to maximise the efficiency of mobile phone manufacturing whatever the flavour of communications standard. The Aeroflex solution is a high performance, high speed modular platform based on an industry standard, PXI. The platform is different by maintaining both open hardware and open software frameworks and in doing so retain the maximum benefits of flexibility offered by the PXI standard and ensuring hardware utilisation is maximised. By working together with customers Aeroflex is revolutionising the way in which mobile terminals are manufactured. Not only is the Aeroflex equipment intrinsically fast responding but Aeroflex software is able to be used in application development that optimises test sequences so that terminal and test equipment idle time is minimised and CPU processing time is utilised optimally. Indeed, the flexibility of the Aeroflex solution can be deployed in new ways so that multiple devices undergo test together each seizing access to the hardware as it becomes available whilst multi-core processors deliver high speed parallel processing.
The author works for Aeroflex
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