Microwave Engineering Europe - September 2008 - (Page 23)

TEST — RF AMPLIFIER PERFORMANCE 23 Analyzing RF ampliﬁer complex modulation performance By Robert Green, Senior Market Development Manager, Keithley Instruments, Inc., Cleveland, OH, www.keithley.com n wireless communication devices, phase and amplitude distortion created by the power ampliﬁer directly affects the quality of the communication. The most signiﬁcant measurement for analyzing power ampliﬁer performance in the latest communication system protocols is the measurement of error vector magnitude, or EVM. This is a measure of modulation accuracy, or how well the power ampliﬁer is transmitting information represented by the varying phase and amplitude of an RF signal. EVM measurements lend insight into the communication link and are the key measure of transmitter performance. On the receiver side, EVM is a measure of how well the receiver demodulated the transmitted signal. I A more direct measure of receiver performance is the BER (bit error rate) measurement. However, EVM measurements are faster than BER measurements and give more insight into ampliﬁer performance. Design and test engineers may tend to think of EVM as a single number representing modulation accuracy, but factors other than those internal to the modulator such as gain error, quadrature error, and carrier feedthrough, can impact EVM. This can include the transmission frequencies, the level of input power to the power ampliﬁer, and the power ampliﬁer DC bias levels. In addition, EVM measurements get more complex with multicarrier modulation techniques such as orthogonal frequency division multiplexing (OFDM). A complete characterization of either power ampliﬁer or transmitter EVM should include analysis of EVM over the range of transmission frequencies, over the expected input power range, and over an allowable range of power ampliﬁer DC bias levels. It is particularly important for mobile devices to characterize transmission, or EVM performance, down to the low-battery shutoff voltage level. For OFDM, EVM analysis versus subcarrier is essential to understanding transmitter performance. With a wide range of existing and new signal protocols and modulation schemes being employed in emerging standards such as WiMax, Ultra Wideband (UWB), and the 4th generation Long Term Evolution (LTE), discovr mor dtails mms.structurs.snsors.olds.acclromtrs.nanowirs. e08_MiEnEu210x140_micna_E.indd 1 023-024-025-026-027-028_MWEE.indd 23 02.07.2008 10:19:31 Uhr 4/09/08 12:31:59 http://www.keithley.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - September 2008

Microwave Engineering Europe - September 2008 News Contents Comment Cover Feature: Uncovering Test and Measurement’s Role in Advancing LTE and Mobile WiMAX WiMax: WiMax and LTE Need to Address Issues of Backhaul, Cost and Efficiency for Successful Deployment WiMax: Manufacturing Communications Technology Products in India Test and Measurement Mobile Platforms Evolve to Meet Future Demands Products Calendar

Microwave Engineering Europe - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.