Circuit testing and analysis
3.1 Basic RF performance test
The basic RF performance of a power amplifier depends on the input-output matching as well as the supply voltage and static bias conditions. In order to make the device more efficient within a certain power range, different supply voltages and static biases can be selected to compromise the requirements of drain efficiency and overall linearity.
Test index requirements and test conditions: In the frequency band from 2496MHz to 2690MHz, the test index requires that the standing wave is less than -10dB, the gain is greater than 34.5dB, and the 3dB compression point is greater than 45dBm.
The test conditions are 24V drain supply voltage and -4.33V auxiliary amplifier bias voltage, 50mA driver stage static operating current, 50mA main amplifier static operating current, 8uS/80uS saturation power test signal, 2500MHz to 2700MHz test frequency range, 25 degrees test environment temperature, and an external fan to keep the temperature constant.
Table 2 shows the results of S-parameter measurement using Agilent E5071C vector network analyzer and measurement using E4438CESG signal generator and E4417A power meter.
Table 2 S parameter and 3dB compression point test results
The test results show that within the frequency range of 2500MHz to 2700MHz, the reflection coefficient of the input port is below -10dB, the small signal gain is around 35dB, the flatness is within 0.3dB, and the 3dB compression point power is above 45dBm. This data can meet the design index requirements.
Circuit testing and analysis
3.2 Linear calibration test
The power amplifiers used in large-scale antenna array systems have extremely strict requirements on linearity. Currently, most manufacturers use digital pre-distortion to improve linearity. This article uses ADI's transceiver module with digital pre-distortion function to linearize QPA2705. The method of use is: Due to the insufficient driving capability of the transceiver module, a driver amplifier is required as a pre-driver, and then the QPA2705 is calibrated for digital pre-distortion linearity.
Test index requirements and test conditions: According to the 3GPP index requirements in the 2496MHz to 2690MHz frequency band, after digital pre-distortion calibration, the adjacent channel power ratio must be less than -45dBc.
The test conditions are to adjust the drain supply voltage according to different power levels, the bias voltage of the auxiliary amplifier is -4.33V, the static operating current of the driver stage is 50mA, the static operating current of the main amplifier is 50mA, the test signal is 7.5dB peak-to-average ratio and 3*20MHz LTE signal, the test environment temperature is 25 degrees, and an external fan is added to keep the temperature constant. 24V power supply is used from 34dBm to 37dBm, and 26V and 28V power supply are used from 37dBm to 38dBm to improve efficiency and ensure linearity.
The indicator requirements of the degree.
Table 3 shows the data of the 2605MHz frequency, 7.5dB peak-to-average ratio and 3*20MHz LTE signal test. Figures 6 and 7 show the initial adjacent channel power ratio and adjacent channel power ratio after digital pre-distortion processing at 38dBm output power. From the test results, it can be seen that for the power range of 34dBm~38dBm, the drain efficiency is 37.9%~44.41%, and the adjacent channel power ratio after digital pre-distortion technology processing can reach about -50dBc. This data can meet the design index requirements.
Table 3 Test data of 2605MHz frequency, 7.5dB peak-to-average ratio and 3*20MHz LTE signal
Figure 6 Initial adjacent channel power ratio
Figure 7 Adjacent channel power ratio after digital predistortion
in conclusion
This article is based on Qorvo's QPA2705 device and ADI's transceiver module with built-in digital pre-distortion function. It studies and tests a highly integrated power amplifier module that can be used in large-scale array antenna base stations. In the frequency range of 2496MHz to 2690MHz, for different power levels from 34dBm to 38dBm, the overall index requirements of drain efficiency and linearity are compromised by adjusting the power amplifier drain supply voltage.
Under the condition of 24V drain supply voltage, in the power range of 34dBm to 37dBm, the drain efficiency is between 37.9% and 44.16%, and the adjacent channel power ratio after digital pre-distortion technology processing can reach about -50dBc.
Under the condition of 26V drain supply voltage, the drain efficiency of 38dBm power can reach 44.41%. At this time, the adjacent channel power ratio after digital pre-distortion technology processing can reach -48.69dBc.
Under the condition of 28V drain supply voltage, in the power range of 37dBm to 38dBm, the drain efficiency is between 40.55% and 42.33%. At this time, the adjacent channel power ratio after digital pre-distortion technology processing is below -50dBc.
It can be seen from this that the QPA2705 power amplifier module can be used in large-scale array antenna base stations.
References
[1] Waitingfor5Gtechnology, MarkLapedus, June 23, 2016.
[2] 5G the Precarious Promise, June 13, 2016.
[3] Howwill5Gwork, MarkLapedus, June23, 2016.
[4] AK Panda, RK Paridd, NC Agrawala and GN Dash, “A comparative study on the high band gap material (GaN and SiC)-based IMPATTs”, in Asia-Pacific Microwave conference, 2007.
[5] Steve C. Cripps. “RFpowreamplifiersforwire-
lesscommunications. 2ndedition". Theartechhouse microwave library,2006: 290-310.
[6]KorneVennema",RFPowerworkshop",June2010.
[7] S. Jee, J. Lee, B. Park, C. Kim, and B. Kim, "GaN MMICboradbanddohertypoweramplifier", inAsia- Pacific Microwave conference, 2013, pp 603-605.
[8] DY-T.WuandS.Boumaiza, "Amodifieddoherty configuration for broadband amplification using sym-metricaldevices", IEEE, pp.3201-3213, Oct.2012.
[9] 3GPP TS 36.101 V14.1.0(2016-09).
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