Application Note

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Overview

Testing of mobile devices is becoming increasingly more stringent and, as a result, a new test is now being standardized to further test performance. As this new type of testing, over-the-air (OTA) testing, is developing, an important parameter, Total Radiated Power (TRP), is becoming increasingly important. Classically, the output power of a power amplifier (PA) has been measured and evaluated into a 50O load impedance; however, the load impedance presented to the PA by the antenna of a mobile device can vary dramatically in real world applications. The cellular industry has realized that a better evaluation of the RF performance of a mobile device can be achieved through OTA testing. In regards to the PA, the Delivered Pout Range (DPR) is significantly affected by varying load impedance, and these affects can be measured through simulated OTA testing. This can give an idea of the TRP performance of the mobile device as a whole. Currently, the most advanced specification on this matter has been put forth by the Cellular Telecommunications and Internet Association (CTIA). The current specification published by CTIA is revision 2.1 of the Test Plan for Mobile Station Over the Air Performance. 3GPP and ETSI appear to also be working on a specification standard, but there is no known publication date as of yet. In addition to the DPR, the harmonics generated by the PA are also affected by the varying load impedance presented by the antenna. The effects of varying load impedance on the PA harmonics can also be measured through OTA testing. Measuring the harmonics is necessary to ensure that the mobile device does not interfere with other signals that are being transmitted. The harmonic content in the output of a mobile device is greatly influenced by the PA. Measurement and specification of the harmonic content of a mobile device have been established for a 50O load conditions as defined in the ETSI/3GPP specifications for GSM systems; however, there is not yet a specification set when performing OTA testing.

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•Application Note: Total Radiated Power (TRP) And Harmonics