Application of LXI Bus to EMC-ATS of Mobile Phone Abstract: This paper is about EMC-ATS of mobile phone based on LXI bus. It gives introduction to its system structure, hardware platform design of test system and software function, as well as audio-frequency test system of mobile phone. Keywords: LXI; Radiation; Anti-disturbance; Audio frequency 1. Overview of LXI bus LXI (LAN eXtension for Instrument) is an instrument platform based on industrial standard Ethernet technology. It is specially designed to provide the standardization, flexibility and high performance for small and medium systems. With compact and flexible structure, high-speed I/O as well as reliable test performance, LXI could meet the needs of research and development in fields of military, automation, industry, medicine, consumer electronics and manufacturing engineers. LXI standard defines small but standardized instruments taking low-cost and open-standard LAN (Ethernet) as the system core. Free from the restrictions of high cost and case structure, LXI could provide standardized instruments with size and comprehensive advantages. Making use of present and future performance advantages of LAN, the standard achieves continuous development and surpasses to a large extent the communication performance of traditional testing and measuring instruments. As the application of Ethernet technology in test automation field, LXI is currently being applied by majority of leading manufacturers in instrument industries. It provides high-performance instruments with a LAN module platform of automation test system as a substitute for traditional test bus technology such as VXI, PXI, GPIB, etc. LXI is the development trend of bus technology in the future. 2. Overall design of EMC test system of mobile phone With the rapid development of communication technology, digital cellular communication system is widely used in the mobile communication field in our country. According to a report released by Gartner, a market survey organization, in 2008, the sales volume of mobile phone will hit 1.2 billion all over the world, among which, that in China will account to more than 1/10, that is, about 0.12 billion, and among them 50 million will be home-made, but the EMC problem becomes ever obvious. With respect to the reality of domestic communication industry, and aiming at EMC of mobile stations and its auxiliary equipment of digital cellular communication system, the Communication Metrological Center of MII (the Ministry of Information Industry) drafted YD 1032-2000 Limit Values and Measuring Methods for 900/1800 MHz TDMA Digital Cellular Mobile Communication System Part 1: Mobile Station and its Auxiliary Equipment, which was proposed by the Telecom Institute of MII and issued by MII on Jan 28, 2000 and put into effect on the same day. This draft requires that only mobile phones that meet this standard can be sold in the Mainland China. At present, mobile phones of GSM, PCS, CDMA and WCDMA systems are widely used, and TD-SCDMA system to be put into debugging will enter the market soon. Mobile phone EMC of any system shall be tested according to relevant standards. As C-type LXI products that adopt LXI bus technology or meet LXI bus specification increases, it is an inevitable trend for LAN to gradually come to control the instruments in EMC test system in place of GPIB; at present, instruments with LAN-based program

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control function in EMC test system are quite few, and the majority is still based on GPIB interface. Thus, the program control bus of this system applies mixed GPIB+LAN model, which does not only meet the need to control traditional instruments but also can be compatible with gradually-increased LXI/C instruments and enlarge bus compatibility of the system. This test system is specially designed for various systems of mobile phone in the market. It has an overall systematical design of radiated stray disturbance, radiated continuous disturbance, and radiated anti-disturbance test of portable phones. By using LXI bus technology and transfer Switching unit, it realizes automation test of system, whose bus topology is shown in Fig. 1.

Power amplifier roomroom

Power amplifier 1 Power amplifier 2

Darkroom

Audio-frequency analyzer Field strength meter Controller Frequency spectrum analyzer

Signal source Power meter

Switch driver Switching unit Comprehensive tester

Power amplifier Signal source Power meter Switching driver Switching unit

Control

Fig. 1 System topology figure The LAN port of computer is connected with LAN router through LAN wire, so does LAN router and LAN/GPIB gateway. GPIB port of GPIB instruments is connected with LAN/GPIB gateway through GPIB cable; the LAN port of LXI/C instruments establishes its direct connection with LAN router through LAN wire; LAN router and computer are put together in the control room, and a LAN/GPIB gateway respectively equipped in the control room, power amplifier room and darkroom realizes switching between buses. 3. Hardware design of the test system

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In view of radiated stray disturbance test, continuous disturbance test and analysis of anti-disturbance test function of mobile phones, the hardware of system mainly includes the following subsystems: base station analog subsystem to accomplish the function of base station in real communication, that is, to connect the mobile phone and control its communication, and the system can be set up with Agilent 8960 or R&S CMU200 comprehensive tester; substitution method subsystem, testing the radiated stray disturbance of mobile phone with substitution method according to standard, is used to restore the received disturbance value to emission value of phone, including signal source, transmitting antenna and cable; audio-frequency monitoring subsystem, whose basic function is to test up and down audio frequency of the communication system before the test and monitor the rank of up audio frequency in the course of test, is equipped with 3560C audio-frequency analyzer from B&K Company which can be connected with audio-frequency output interface of comprehensive tester; others are disturbance collecting subsystem, anti-disturbance subsystem, data-processing subsystem, switching unit subsystem, etc. The radiated stray disturbance is mainly the stray disturbance signal tested from mobile phone shell under a special mode and of course the stray disturbance caused by transmitter. Under the idle mode, test the stray disturbance signal transmitted from the shell, inner structure and inner connecting cable of the phone. Given that phone frequency varies from 80MHz～12.75GHz in different systems, the receiving antenna is switched automatically by a switching unit according to the test frequency, and the mobile phone is initialized before the test in accordance with relevant standards. As shown in Fig. 2:

Radio wave semi-darkroom

Communication antenna

Comprehensive tester

Audio-frequency link

Switching driver Computer

Switchboard

Frequency spectrum analyzer

Filter

Signal adapter plate Rotation desk

Switching unit Receiving antenna unit

Controller

Mobile phone Rack

Antenna tower

Fig. 2 Schematic diagram of radiated stray disturbance measurement of mobile phone The power level of radiated stray disturbance is determined by “substitution test method”

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and transmitted by substitute phone of pre-corrector in the radio wave darkroom, that is, to replace phone with signal source and transmitting antenna, so that the radiated stray disturbance test receiver could get response of the same power, and the power transmitted by the pre-proofreader is the power level of radiated stray disturbance. With respect to the radiated continuous disturbance, the stray disturbance signal from the shells of mobile phone and its auxiliary equipment (charger) as the main objects is tested. Compared with that of radiated stray disturbance, the test frequency band of this test is far smaller, and the test is much easier, while the arrangements and hardware configurations of both are similar. In the radiated anti-disturbance test, the radiated anti-disturbance of the port in the phone shell is tested. This test checks the endurance of mobile phone in the radiated electromagnetic field, and examines whether its performance is reduced or has a breakdown. In the test of radiated anti-disturbance, under normal communication situation of the phone, the transmitting antenna radiates a certain quantity of field strength (standard 3 V/m, distance of 3 m) within the corresponding test frequency band, and the audio-frequency level of phone is monitored by the audio-frequency tester to judge whether the EMC performance at phone terminal is qualified or not. The radiated anti-disturbance audio-frequency calibration test is as shown in Fig. 3 and audio-frequency test in Fig. 4 which shall be conducted in semi-darkroom.

Radio wave darkroom 1 kHz test source

Comprehensive tester Audio-frequency output Computer

Switchboard

Audio-frequency

Radiofrequency link

Acoustic pipe

1 kHz test source

Audiofrequency analyzer

analyzer

Note: EUT is located as shown in case of up-link calibration; there is no EUT in case of down-link calibration Fig. 3 Diagram of radiated anti-disturbance audio-frequency calibration test In view of varied systems whose frequencies range from 80MHz～6GHz, the radiated anti-disturbance test needs 3 power amplifiers and 2 sets of transmitting antenna to realize automatic control through switching unit and monitor the magnitude of field strength with field strength probe; the audio-frequency analyzer analyzes the signal which is output from comprehensive tester and ear simulator and collected by the filter, to evaluate the signal-receiving quality of mobile phone.

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Radio wave darkroom

Comprehensive tester Audio-frequency output

Computer

Radio-frequency link

Switch board Audiofrequency analyzer

Directional coupler

Transmitting antenna unit

Field strength probe

Switching driver Signal source

Switch Power ing amplifier unit group

Seal

Audio-frequency analyzer Power meter

Field strength meter

Fig. 4 Diagram of radiated anti-disturbance test The audio-frequency system adopts special audio-frequency equipment made by Denmark company B&K, which is the first-class sound testing instrument manufacturer in the world. The system configuration in phone test includes 3560C portable audio-frequency test system, 4602B phone test head (including 4227 mouth simulator, 4185 ear simulator and 4231 sound pressure calibrator), 2716C audio-frequency amplifier, 2690 microphone amplifier with double-channel filter function whose channel 1 amplifies and filters the audio-frequency signal of the microphone, which will then be analyzed and processed after entering into 3650C audio-frequency analyzer, and channel 2 filters the audio-frequency signal transmitted by comprehensive tester before it is analyzed and processed in 3650C audio-frequency analyzer. The 3560C audio-frequency test system communicates and exchanges data with the computer through LAN. The signal processing is mainly finished by this system, which can also generate test signal for the tested object. As for different darkroom structures, appropriate arrangement of all components of the audio-frequency analyzing system should be taken into consideration. Such as 2716C audio-frequency amplifier put in the darkroom, it, when mainly used for audio-frequency calibration, tests the reference levels of up-chain-circuit and down-chain-circuit sound output signals, and amplifies 0dBPa and -5dBPa audio-frequency signals obtained respectively at ERP (ear reference point) and

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MPR (month reference point) of mouth simulator while it is transmitting 1kHz. ERP refers to the located point at the entrance of otocleisis of the hearer, and MPR the point 25 mm right ahead the lip axle of artificial mouth. 4. Software design of the test system Software is an important part of mobile phone test system. According to the analysis on hardware, all the rest have relation with software except the base station analog subsystem, which establishes communication connection with mobile phone mainly through antenna without involving signal data processing, thus there is no need for software system. The independently-developed mobile phone EMC test system is designed with Chinese interface easy to operate; it can realize software control over the main test instruments. Through the special control equipment for software in the control room, the instruments can be set up and operated; and switching between the test items is automatically accomplished through the program. The software could control the frequency spectrum analyzer, signal source, comprehensive tester, audio-frequency analyzer, rotating table/antenna tower controller and switch unit, develop the control module through IVI technology, and control test instruments of the same type produced by different manufacturers. The test control is carried out in the procedures required by relevant standards of different systems. The data analysis includes frequency point catch, test curve analysis and data leading-in and -out. Frequency point catch mainly refers to the catch of standard-exceeding point, warning point and arbitrary point: to abstract the corresponding frequency point (frequency and amplitude) from the test curve. The test curve analysis is to draw the test data into a frequency spectrum curve to compare it with the relevant limit values and then analyze and process it appropriately. Data leading-in and -out refers to the leading-in and -out of the test curve, signal list and correction coefficient. Report processing is to save or print the reports of test equipment, test curve and special frequency point (non-standard or other appointed frequency points) with illustrations and texts. 5. Conclusion The test system realizes its automatic control over each test item by means of LXI bus control, which is not only cost effective but also beneficial for the expansion and upgrading of the system. By adopting the hardware equipment of well-known manufacturers, its reliability is guaranteed. Besides, the test software developed based on IVI technology greatly enhances test efficiency and system management ability. References 1. YD 1032-2000 EMC Limit Values and Measuring Methods of 900/1800 MHz TDMA Digital Cellular Mobile Communication System Part 1: Mobile Station and its Auxiliary Equipment. 2．ETS 300 342-1 Radio Equipment and Systems （RES）, Electromagnetic Compatibility （EMC） for European Digital Cellular Telecommunications System（GSM900MHz and DCS1800MHz）Part1: Mobile and Portable Radio and Ancillary Equipment. 3. Yu Liangying. Interference Test of Mobile Phone, China Science and Technology Information, 2006, 19. 4. YD/T 1050-2000 General Test Specification on 800MHz CDMA Digital Cellular Mobile

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Communication Network Equipment: Mobile Station Part. 5. GB9254-1998 Radio Interference Limit Values and Measuring Methods for Information Technology Equipment.

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