Microwave Engineering Europe - September 2008 - (Page 25)

TEST — RF AMPLIFIER PERFORMANCE 25 ratio. It can be used to determine the physical error introduced at different stages of a communication system, which helps designers troubleshoot speciﬁc problems. Another advantage is the simplicity of the measurement set-up. An RF vector signal generator is needed since a signal source is needed to generate the modulated signal that the RF system will be transmitting and receiving. The DUT signal output is acquired and analyzed with a vector signal analyzer which has the capability to decompose the received signal into its I and Q components and demodulate or recover the original transmitted state. Based on the measured I and Q values, the EVM is computed referenced to the ideal I and Q values for the demodulated state. The complexity is either in the internal algorithms or the external software built in to the instruments to generate and analyze the various modulation schemes. If the algorithms are built into the instrument, both the speed of signal generation and signal analysis is increased relative to having to transfer large amounts of data to and from a PC for processing. The constellation display shows how increasing EVM causes overlapping states and bit errors to occur. With different modulation schemes, the same EVM can have different bit error rates since the symbol states are closer or further apart. The technical effects are increased data errors, which can also be seen as reduced voice quality or reduced channel bandwidth in TCP/IP systems where Internet packets must be resent. The economic effects potentially include higher product costs, lower product sales, and lower proﬁtability. EVM measurements Figure 2 shows a typical EVM measurement set-up. The device under test (DUT) is a power ampliﬁer designed to transmit signals in conformance with the GSM/EDGE cellular standard. The EVM performance of its EDGE modulation will be tested. A vector signal generator (VSG) is used to produce the RF signal with the required frequency, amplitude, and EDGE modulation. The RF signal is sent through the power ampliﬁer and demodulated in the vector signal analyzer (VSA), which measures and calculates the EVM. The frequency reference for the VSG and VSA is connected together. This removes any relative frequency error between the two instruments and signiﬁcantly increases measurement speed. The two instruments are connected to a computer via their LAN (LXI) or GPIB ports. There are various requirements a typical user may have for analyzing a power ampliﬁer’s modulation performance in a characterization or a manufacturing environment. In this example, EVM will be measured across the operating frequency range of the ampliﬁer and with a range of power levels to determine how power ampliﬁer EVM is impacted by frequency and input power level. Also important is ensuring sufﬁcient accuracy for the measurements. Measurement accuracy directly contributes to product quality and yield. This indirectly affects the product revenues through satisﬁed customers and product cost through decreased rework, returns, and scrap. In addition, fast EVM measurements are important. Measurement time contributes directly to product cost. In general, the lower the test time the lower the product cost. Figure 3 shows the vector signal analyzer set-up parameters display and the results for the EVM versus input power measurement. The user interface on newer RF instruments can usually Register online and enjoy the beneﬁts: www.electronica.de/ticket discover more details mems.structures.sensors.oleds.accelerometers.nanowires. get the whole picture electronica micronano-systems at the world’s leading trade fair for key future technologies. Discover tomorrow’s most important topics and trends today. Expand your knowledge and make valuable contacts in all of the important sectors and at all levels of the microelectronics industry. www.electronica.de/micronano. Be sure to visit the concurrent trade fair www.hybridica.de electronica 2008 micronano-systems 23rd world’s leading trade fair New Munich Trade Fair Centre November 11–14, 2008 e08_MiEnEu210x140_micna_E.indd 2 023-024-025-026-027-028_MWEE.indd 25 02.07.2008 10:19:31 Uhr 4/09/08 12:32:15 http://www.electronica.de/ticket http://www.electronica.de/micronano http://www.electronica.de/micronano http://www.hybridica.de

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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

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