Test bus for automatic test system design

The development of modern science and technology such as microelectronics, computers, sensors and information processing technology has provided favorable conditions for the development of automatic detection technology, laid the foundation for the new generation of ATS, and become a powerful driving force for the continuous progress of its architecture, test methods and test technology. The research of automatic test equipment (ATE) and automatic test system (ATS) has become the focus of development in countries around the world. At present, in terms of ATS technology, standardization, modularization and serialization have become the inevitable trend of development. Standardized bus technology is the key technical foundation for the development of ATS. At present, in the field of automatic testing, multiple bus technologies coexist, presenting a situation of "letting a hundred flowers bloom and a hundred schools of thought contend". The main test buses include VXI, PXI, LXI and AXIe.

1 VXI and PXI bus

The VXI bus specification was approved as IEEE-1155-1992 standard by IEEE Standards Bureau in September 1992. VXI bus is an outstanding representative of modular test instrument, with stable power supply, strong cooling capacity and strict RFI/EMI shielding. It has the characteristics of compact structure, strong data throughput, accurate timing and synchronization, and is suitable for building large and medium-sized automatic measurement systems and applications with high speed and precision requirements. VXI is mainly used in large ATE systems, aviation, aerospace and other defense and military fields.

The PXI System Alliance led by NI was established in September 1997. PXI (PCI eXtensions for Instrumentation) is not only a bus technology, but also a modular I/O standard based on PC technology, adding integrated timing and synchronization functions, industrial-grade rugged design, and more channels to the PC-based automated test measurement and control system architecture.

2 LXI and AXIe bus

In September 2004, the LXI bus consortium led by Agilent was established. In 2005, the LXI standard version 1.0 was released and the first batch of LXI modules were launched. The infrastructure of the LXI bus is Ethernet. High-speed Ethernet is used to realize global networking of instrument systems from local to wide areas, and the global timing synchronization of the entire instrument system is obtained by relying on the IEEE1588 precise timing protocol. The purpose is to build a new generation of test and measurement systems with simple, economical, high-speed and practical hardware and software, and its purpose is to replace the GPIB bus that has been used for 40 years. In

November 2009, Agilent Technologies, Aeroflex and Test Evolution jointly established the AXIe Alliance to develop and promote the AXIe series of standards. AXIe was initially formulated with reference to existing standards such as AdvancedTCA, PXI, LXI and IVI. It is an open standard based on AdvancedTCA. Its goal is to create a dynamic system composed of components, modules and instruments to promote the development of general instruments and modular testing. The AXIe standard provides maximum scalability to meet the needs of various platforms, including general-purpose rack-and-stack systems, modular systems, semiconductor ATE systems, as well as workbenches and modular plug-ins.

3 Comparison of PXI, LXI, and AXIe

The PXI bus has a higher bus bandwidth and very low transmission latency, which is unmatched by other buses. At the same time, PXI can achieve higher speeds and greater bandwidth by upgrading to the PXI Express bus, but the modular design of the PXI bus limits its ability to expand to larger-scale and wider-area automatic test systems. The

LXI bus is based on Ethernet, so it has strong expansion capabilities, but because it adopts instrumented design, it does not have an advantage in cost, and has certain limitations in software development and transmission rate.

Compared with VXI and PXle bus technologies, AXIe can provide larger PCB size, output power, efficient heat dissipation, high-speed and flexible data communication architecture, and the flexibility of the AdvancedTCA standard, while also being compatible with the AdvancedTCA standard. Its main features are a module circuit board with an area of ​​900 cm2; a local bus with up to 62 channels that allows the data transfer rate between adjacent modules to reach 600 Gbit·s-1; a low latency and high-speed PCI bus that allows the data transfer rate between instruments and computers to reach 10 Gbit·s-1; industry standard and flexible LAN communication, as well as buses and radial distributed timing and triggering that can be used for instrument synchronization.

4 ATS design based on AXIe bus

AXIe adopts a layered architecture and is built on the AdvancedTCA standard (PICMG 3.0 and 3.4), which can provide features such as large PCB, LAN, PCIe and system management. The AdvancedTCA-based AXIe1.0 standard is suitable for general-purpose instruments and adds core trigger functions, timing functions and high-speed local buses. AXIe1.0 implements the above functions on the backplane zone 1 and zone 2 connectors without specifying the rear panel connector or using the module or backplane zone 3 interface. AXIe1.0 can also be extended for specific application areas, such as semiconductor testing (AXIe3.1), and may include provisions for module rear panel connections.

AXIe instruments can be integrated with existing standard PXI, LXI, and IVI based instruments in a typical rack-and-stack configuration. For example, PXI instruments can be mounted vertically in a rack and use rack-mounted, embedded, or desktop controllers. AXIe modules mounted horizontally in the same rack can be used as virtual PXI or LXI instruments. LXI synthetic instruments can also be added to the rack.

 

AXIe instrument modules based on PCIe can act as control computers like PGIe modules, and work in the same way as PXI instrument modules. AXIe instrument modules based on LAN can act as control computers like network nodes, and work in the same way as LXI instruments. All of these instruments can use drivers that comply with the IVI standard and can run in all application development environments. The

hardware structure of a certain type of ground test equipment fault diagnosis automatic test system based on the AXIe bus is shown in Figure 1.

 

The software system includes functional modules such as test diagnosis platform, user interface, data information management platform and online help. The test diagnosis platform completes the test diagnosis program to diagnose and locate the faults of the instrument under test according to the diagnostic steps, simulation stimulus, data stimulus, signal type, test node, instrument operation, etc. input by the operator, and provides automatic monitoring and information prompt functions; the user interface generates the display content of the diagnostic execution interface and completes the interactive setting of the human-machine interface; the data information management platform completes the equipment fault statistics and board-level fault statistical analysis, fault trend analysis and pre-test functions, and realizes the integration of fault diagnosis test and information analysis feedback. The test software is developed using LabVIEW. LabVIEW software provides good support for AXIe devices and can achieve seamless connection of test data. The browsing interface is composed of test software, as shown in Figure 2.
 
5 Development Trend of Automatic Test System

Through the comparison of test buses such as PXI, LXI and AXIe, it can be seen that for automatic test systems, the ultimate goal is to provide high-speed, highly automated and highly compatible test equipment and programs. Its development trend will continue to develop in the direction of standardization, serialization and modularization, while increasing the use of new system buses, high-performance computers, artificial intelligence and expert systems and other new technologies to further improve the comprehensive performance of ATE/ATS. At the same time, ATS equipment will develop in the direction of miniaturization, portability and generalization. In order to reduce costs, the measurement and control system will adopt a large number of COTS technologies to further enhance the interchangeability and interoperability of the system, ensure the advancement, maturity and stability of the system, focus on the design concept of comprehensive diagnosis support system, and develop towards the open structure of integrated fault diagnosis and test system. The measurement and control bus will present the characteristics of multiple buses coexisting, but the ultimate result of the measurement and control bus is to achieve the unification of bus technology with the development of computer technology.