Flexible and Modular Approaches to Multi-Device Testing by Robin Irwin Aeroflex Test Solutions Introduction Testing time is a significant factor in the overall production time for mobile terminal devices, and the industry is constantly looking for ways to minimise both this time and the associated costs. Significant progress has been achieved with the introduction of non-signalling test, which removes the need for protocol-based testing by utilising the proprietary test modes within the chipsets. The testing of multiple devices at the same time is now a key goal, a variety of different scenarios for testing multiple devices under test (DUT) are described here, including an analysis of various device configuration, RF routing and test control options, along with the respective design considerations and strategies. An off-the-shelf solution to parallel multi-dut testing is presented that significantly increases the efficiency of utilisation of production test equipment. Multi-DUT design considerations The main elements of a device test system that can be reconfigured for multi-dut testing are: 1. RF test resources: for most applications a RF signal generator and RF signal analyzer are the key items of test equipment for non-signalling test. Hence a RF test resource is defined to be one of these instruments - the RF signal generator provides a stimulus to the device(s), and the RF signal analyser is used to analyze the output from the device(s). A RF channel is defined as a combination of one signal analyser and one signal generator 2. RF conditioning: the RF routing and interconnection between the RF test resource(s) and the antenna port(s) of the DUT(s). 3. RF fixturing: additional RF routing, device handling or external equipment that is considered external to the test equipment but still necessary for production flow. The key to multi-dut testing is to configure both the RF conditioning and the software that controls it in order to improve test system efficiency for a number of devices at once. In practice the devices that need to be tested will have multiple antenna ports each either serving different radio technologies and/or supporting the use of diversity or MIMO techniques as shown in Figure 1, which introduces additional challenges. Several multi- DUT testing options have been identified and evaluated, and these are described in the following sections.
Figure 1: Multiple antenna ports on a typical modern smartphone Option 1: Multiple RF channels In this scenario each RF channel is mapped with a one-to-one relationship to a specific device, and each device is tested asynchronously as shown in Figure 2. Figure 2: Testing multiple devices using multiple RF channels Page 2 of 7
This approach is best implemented with modular test equipment, where additional channels can be added as required and where the RF signal conditioning can also be specific to the device requirement. A traditional one-box-test approach is possible, but is likely to be less flexible as, for example, it may not provide a range of RF signal conditioning options. This would mean that function would need to be provided externally to the test equipment, typically in additional fixturing requirements. Figure 2 shows a multiple RF channel configuration with a shared controller, which can be external or embedded as part of the test instrumentation, but equally a dedicated PC controller could be used for each channel. When moving from a single RF channel to multiple channels, careful design is required to avoid interference. It is also necessary to consider how to identify a given device in the test flow within the test executive when the channel count per test station has been increased. Option 2: Multiplexing RF resources This is where RF resources are multiplexed sequentially between different DUTs. Two examples are shown in Figure 3. (a) (b) Figure 3: Multiplexing RF resources to test mobile devices sequentially (a) Full duplex, and (b) Half duplex (ping-pong) The arrangement in Figure 3(a) allows for full duplex multiplexing where each device is tested sequentially, which suits a Frequency Division Multiple Access (FDMA) setup where the transmitter and receiver can be tested in parallel. Figure 3(b) shows a receiver on one device being tested while on the other device the transmitter is tested, after which the connections are reversed to complete the tests. This is sometimes referred to as Tx/Rx pingpong testing. In this scenario each device can use an independent RF resource - an example of half duplex testing that is suited to a Time Division Duplex (TDD)/Time Division Multiple Access (TDMA) setup. Page 3 of 7
Option 3: Sharing RF resources The example in Figure 4 shows RF resources being shared simultaneously between multiple DUTs. Figure 4: RF resources being shared simultaneously between multiple DUTs Option 4: Combinations Multiplexing and sharing RF resources The final scenario - shown in Figure 5 - combines elements of the previous approaches inside the RF conditioning, providing the ability for resources to be both multiplexed and shared. It illustrates a high utilization of the RF resources with a broadcast downlink (which allows for parallel receiver testing) and switched uplink. Figure 5: Combination of multiplexing and sharing RF resources Modular RF resources in a test platform In order to enable multi-dut test in practice, it is essential to choose a test platform architecture that is flexible enough to meet the demands of different multi-dut scenarios. Firstly, it is necessary to be able to scale the test system to add a RF channel, providing flexibility and expansion without increasing the footprint. Secondly, it requires the ability to dynamically assign and un-assign a RF resource, This is so that the test executive (which integrates the modular software controls to the test instrumentation) is in charge of the test flow and its flexibility, and is not inhibited either by the architecture of the instrument or by Page 4 of 7
its application programming interface (API). A further prerequisite is the ability to control a RF resource generically and independently of the parameter being tested, which gives better flexibility in software and hardware architecture. Electronically configurable RF conditioning As mentioned earlier, the devices under test have multiple antenna ports as shown in Figure 1. It is therefore necessary to understand how to use RF conditioning to address these multiple ports. If a test vendor can supply a range of modular RF conditioning options, this allows the system engineer to think more flexibly, and when this is component that can be Integrated into the system and configured electronically, the engineer acquires the capability to control the RF routing from the test executive, as an integral part of the overall system. Simplifying the adoption of parallel multi-dut testing is dependent not only on the specifications of the hardware being designed into a system, but also on the ability of test vendors to supply these parallel multi-dut setups with optional modular device driver plugins that support leading cellular chipsets. If these plugins are available then the time taken to deploy multi-dut techniques in volume for specific chipsets can be dramatically reduced for both R&D and production. Modular software architecture In addition there are some more general advantages of software modularity that can help the test engineer, beyond the ability to support or plug in different chipsets. Software architecture is important for the system and test engineer in order to control and specify tests to individual requirements. Complex test solutions incorporating many system components are often perceived to be closed architectures that cannot be customised, but with a modular software architecture this is not the case. Equally, there is a balance to be found in simplifying the process the test engineers needs to follow in order to get to market quickly, and avoiding what could otherwise be significant test integration effort and complexity. This is achieved by abstracting away from specific RF conditioning/routing, power supply units and devices, allowing the test engineer to develop customisable modules. An example of such a software architecture is shown in Figure 6. Conventionally, the vast majority of logic is contained within the customer application or test executive, where the software uses instrument and device driver API calls to execute testing. Page 5 of 7
Figure 6: Typical software architecture for user control of multi-dut testing Commercial multi-dut system All the above objectives have been realized with the introduction of PXI Maestro (Figure 7), a next-generation wireless device ATE system for use in manufacturing with the ability to test multiple devices in parallel. By adding multi-dut capability to the PXI 3000 cellular and wireless test platform, PXI Maestro provides a production-ready test system with integrated chipset-specific device control that lowers test and test system development costs. It also sets a new speed benchmark for non-signalling mode RF test system integration and test execution. Figure 7: The PXI Maestro multi-dut production test system, used with the Aeroflex PXI 3000 Series modular test platform The ability to test up to eight devices in parallel in a single 19 chassis is achieved using a dual-channel Multi-UE architecture, incorporating a multi-way active RF combiner Page 6 of 7
module that supports connection of up to four devices to each channel. This approach achieves an almost four-fold throughput improvement per radio when compared with an equivalent serial test method, for virtually the same cost. The system is optimized for speed regardless of whether it is implemented to test a single device or multiple devices in parallel. The key to RF test system efficiency lies not just in raw test speed but also in optimizing test equipment utilization. Efficient test system development minimizes equipment idle time both within and across measurement steps. PXI Maestro features a multi-threaded intelligent sequencer to exploit the benefits of modern multi-core PCs, ensuring that different tasks both within a measurement step and across a measurement sequence are overlapped or executed concurrently rather than sequentially as with conventional instrumentation. Multiple threads manage device control, test equipment setup and measurement processing in a tightly coupled manner. Where multiple different measurements are performed at the same test condition then PXI Maestro saves time and executes them in parallel on the same captured data. Support for the direct control of leading cellular chipsets and wireless connectivity are included - the integration of both device and test equipment control under a single programming user interface is a powerful alternative to using separate silicon vendor device and test vendor programming interfaces. The user need only describe the content of the test plan, and the rest of the process takes place automatically. The programming API can be integrated into any customer test executive with varying degrees of configurability of the test execution available. Equally, test execution can be controlled with an optional off-the-shelf GUI. Conclusion A variety of options and approaches exist when considering the design of a multi- DUT system. These can be realized using modular hardware and software. Moreover, a commercial production-ready ATE system solution to parallel multi-dut testing has been described, including integrated chipset control, which is equally beneficial to both large and small manufacturers. This addresses the pressure and growing challenges concerning system engineering complexity, and where test efficiency is a critical business need. This ATE system offers unprecedented speed and flexibility, based on a mature and proven production test platform. Up to eight mobile devices can be tested in parallel, giving an almost four-fold improvement in test throughput. Page 7 of 7