Measuring RF parameters in GSM/EDGE power amplifiers

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Measuring RF parameters in GSM/EDGE power amplifiers
Oct 1, 2006 12:00 PM By Antonio Eguizabal

GSM/EDGE RF power amplifiers used in mobile communications in North America, Europe and elsewhere must conform to a strict ETSI standard in order to obtain type approval by the end user, the service provider and the public in general. In this article, a method for conducting RF lab measurements is presented using commercially available test equipment and following common RF practices. Usually, this involves testing in four bands and two modes.

Bench calibration

No PA module is required, only the input and output component sections. The input insertion loss is determined first, then the output section loss. The first is entered as an offset in channel 1 of the RF power meter, thus moving the measuring plane exactly at the input of the PA. The second is entered as an offset in channel 2 of the same meter, thus moving the measuring plane exactly at the output of the PA.

Proceed as follows:

Isolate the input section.
Calibrate and zero both channels of the RF power meter. Set to the desired frequency.
Set the RF signal generator to 0 dBm CW output connected to the input section.
Connect channel 1 power sensor to the coupled port at the directional coupler. Connect channel 2 to the output of the input section.
Measure the insertion loss in dB by taking the difference in dBm between channel 2 and 1 readings.
Enter this value as a channel 1 offset in the RF power meter.
Confirm that both channel 1 and channel 2 measure exactly the same value. If not, repeat the procedure.
Isolate the output section.
Apply 0 dBm CW from the RF signal generator connected to the load attenuator input.
Connect channel 2 power sensor to the directional coupler main output.
Load the coupled port with a 50 Ω termination.
Measure the insertion loss in dB by taking the difference between 0 dBm and channel 2 reading.
Enter this value as channel 2 offset in the RF power meter.
Confirm that the channel 2 reading is 0 dBm. If not, repeat procedure.

Conclusion

A method for measuring RF parameters in mobile handset power amplifiers is presented with a bench test equipment line-up and its calibration method. A summary table containing the minimum standards set out by ETSI for GMSK and EDGE modulation is given to facilitate the user's access and understanding of the limiting values. Representative power amplifier waveforms are shown from a typical RF power amplifier under test using the methodology herein described.

References:

US CFR Title 47, Part 24, § 24.232(c) (“Mobile/portable stations are limited to 2 W EIRP peak power and the equipmentmust employ means to limit the power to the minimum necessary for successful communications.”) See also US CFR 47, Part 24, §24.52 ”RF Hazards.” These are FCC regulations from www.fcc.gov.
ETSI TS 100 910 Digital Cellular Telecommunication System-Radio Transmission and Reception-3GPP TS 05.05. European Telecommunications Standard Institute (ETSI Sophia Antipolis France, available from www.etsi.org).
ETSI GSM 11.10 Digital Cellular Telecommunication System-Mobile Station Conformance Specification. European Telecommunications Standard Institute (ETSI Sophia Antipolis France, available from www.etsi.org.

Table 1. GSM and EDGE minimum system parameters.
Parameters	Typical RF PA No. 1	Typical RF PA No. 2	System Specifications	ETSI Section
Bands	850; 900; 1800 & 1900 MHz	850; 900; 1800 & 1900 MHz	GSM; EGSM; DCS & PCS	GSM05.05: § 2.0
Power Class	+33 dBm 850/900 +30 dBm1800/1900	+34.7 dBm 850/900 +32.4 dBm1800/1900	+33 dBm (class 4) +30 dBm (class 1)	GSM05.05: § 4.1.1
Power Levels	Power control range is ≥55 dB (Vramp 0.1 to 2.2 V)	Power control range is ≥55 dB (Vramp 0.1 to 2.2 V)	PL5 to PL19 for 850 & 900 bands PL0 to PL15 for 1800 & 1900 bands	GSM05.05: § 4.1.1 (in 4 Tables) GSM11.10 Tables 13-2 & 13-3
Power vs. Time	Not given	Not given	GMSK time mask for MS	GSM05.05: Annex B
Modulation Spectrum GMSK	Not given	Not given	≤-30 dBc @ ± 200 kHz ≤-60 dBc @ ± 400 kHz etc.	GSM05.05: § 4.2.1 GSM05.05: Annex A GSM11.10: § 13.4
Switching Spectrum	Not given	Not given	≤ -23 dBm @ ± 400 kHz ≤ -26 dBm @ ± 600 kHz etc.	GSM05.05: § 4.2.2 GSM11.10: § 13.4 Tables 13-9 & 13-10
Spurious Conducted	-30 dBm LB & HB harmonics	-13 dBm LB harm. -30 dBm HB harm.	≤ -36 dBm over range 9 kHz to 12.75 GHz	GSM05.05: § 4.3.3 GSM11.10: § 12.1
Spurious Radiated	System and circuit design dependent	System and circuit design dependent	≤ -59 dBm worst case 30 MHz to 12.75 GHz	GSM05.05: § 4.3.3 GSM11.10: § 12.2 and Table 12.9
Modulation Accuracy GMSK	Not given. Mostly system and circuit dependent	Not given. Mostly system and circuit dependent	Peak phase error ≤ 20 ° rms phase error ≤ 5 °	GSM05.05: § 4.6.1 GSM11.10: § 13.1
Modulation Spectrum EDGE	≤ -33 dBc@ ±200 kHz ≤ -57 dBc@ ±400 kHz ≤ -63 dBc@ ±600 kHz	≤ -33 dBc @ ± 200kHz ≤ -57 dBc @ ± 400kHz ≤ -63 dBc @ ± 600kHz	≤ -30 dBc @ ± 200 kHz ≤ -54 dBc @ ± 400 kHz ≤ -60 dBc @ ± 600 kHz	GSM05.05: § 4.2.1 Tables a1; b1 and c1
Modulation Accuracy EDGE	EVM ≤ 6% rms worst case	EVM ≤ 6% rms worst case	EVM ≤ 9% rms ≤ 30% peak	GSM05.05: § 4.6.2
Frequency Error	N/A	N/A	≤ 0.1 ppm (i.e., 85 Hz @ 850 MHz)	GSM05.10: § 6.1 GSM11.10: § 13.1
Residual Output Power	Po= -25 dBm max (Fwd Isol 2) Vramp = 0	Po= -25 dBm max (Fwd Isol 2) Vramp = 0	≤ -36 dBm or ≤ -59 dBc whichever is greater	GSM05.05: § 4.5.2 GSM11.10: Table 13-4

ABOUT THE AUTHOR

Antonio L. Eguizabal is an applications engineer with Freescale Semiconductor's RF Devices Division in Tempe, AZ. He obtained his B.Sc. E.E. (Hons) at the University of Santiago and his M.A.Sc at the University of British Columbia, both in Electrical Engineering specializing in Electronics. He was awarded one patent in 2003 and has several years experience with RF power amplifiers for mobile use. He can be reached at a.eguizabal@freescale.com.

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