Nokia Siemens Flexi 3x90W FXEB 1800MHz base station teardown: Power amplifier (part 2 of 2)

This Nokia Siemens Networks Multiradio BTS FXEB module is a GSM 1800 MHz 90W amplifier module capable of GSM/EDGE, WCDMA/HSPA and LTE.

If you missed part 1, see it here: Nokia Siemens Flexi 3x90W FXEB 1800MHz base station teardown: Power amplifier (part 1 of 2)

The Flexi Multiradio Radio Frequency Module (FXxx) or RF Module, is a 3-branch multicarrier, multi-standard radio transceiver module. The module consists of three independent branches, capable of transmitting and receiving signals of multiple radio technologies concurrently.

Up to 6 GSM carriers with 400 KHz minimum carrier separation
Up to 4 WCDMA carriers with 4.6 MHz minimum carrier separation
Multi-carrier LTE signal with 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, and 35 MHz carrier bandwidth
Multi RAT operation with combination of GSM, WCDMA, and LTE

Above pictures shows the coaxial cavity band pass filter which in popular speech is called a duplexer or diplexer. Duplexer band pass filter explained: https://youtu.be/HNaAQ3a7Duc?t=74

The power amplifier consists of a series of a general purpose amplifier, hybrid couplers to split the signals and power amplifiers.

First identifiable IC is a NXP MW7IC2040N 1805 – 1990 MHz capable of 40 Watt CW which feeds a single signal into the Anaren Xinger III X3C19P1-03S and X3C19P1-05S bybrid couplers to split the signal out, phase shifted to the three Ampleon BLF8G20LS-200V 1800 – 2000 MHz capable of 200 Watt.

One output circulator is used for double protection against reflected energy from the duplexer and antenna array. A interesting note about this amplifier module is that it only needs to be supplied with +28VDC, GND and PA_EN pulled high with 3.3VDC to start working. Adjustment for load balancing the LDMOS output transistors is done by a LM75A temperature IC and a digital potentiometer on I2C bus to control the bias of the transistors.

The system boards 4 ADC/DAC main processors are unknown HI FPGAs that has a generic part number which is not identifiable.

A Altera Arria II GX EP2AGX260 FPGA seems to be the heart of the unit and does all system control and communication with other units of the system. It has 16 transceivers that can run up to 550 MHz. 102600 Adaptive Logic Modules and 244188 Logic Elements available.

The analog to digital signal path for the RX diversity starts with the NXP BGU7062 which is a Low Noise Amplifier working in the 1710 – 1785 MHz region. A Anaren Xinger 1P503S 3dB hybrid coupler phase shifts the signal before entering the ceramic resonator filter. (explained here: https://youtu.be/h9-KhfQM3nI?t=729 ).

The RX/TX signal path are both a part of the signal suppliers for the power amplifier. The RX part consists of a Analog Devices ADL5811 Mixer and IF amplifier that works as a downconversion mixer (explained here: https://youtu.be/qO127zY3voE?t=865 ) which by the use of a local oscillator can bring down the carrier frequency of the signal to something lower that is easier to work with for the Analog Devices AD9255 14-bit ADC with a bandwidth of 125 MSPS.

The TX part consists of a Analog Devices AD9122 16-bit DAC with dual 1230 MSPS bandwidth feeding a analog signal through a Low Noise Amplifier and ceramic band pass filter before going to the power amplifier.

The internal clock for the up- and downconversion mixers is generated by the Analog Devices ADF4106 6 GHz PLL.

For the RX Main the analog to digital signal path starts with a Analog Devices ADL5356 1200 – 2500 MHz dual Mixer and IF amplifier that works as a downconversion mixer feeding down through SAW filters (explained here: https://youtu.be/qO127zY3voE?t=963 ) which feed into two Macom MAATSS0015 Digital Attenuators with a 4-bit resolution to provide 15 dB scale at DC – 2 GHz. Additional SAW filters are in place before the Analog Devices ADL5202 Variable Gain Amplifier that has a working bandwidth of 30 – 200 MHz, which also shows that the signal was downconverted earlier. On the opposite side of the PCB the Analog Devices AD80286 14-bit ADC is located with a dual bandwidth of 155 MSPS outputting a single bit stream to the Nokia Siemens protocol encoding FPGAs.

Power supply layout with a single bridge, planar transformer, output diode and output choke for each amplifier and one housekeeping power supply.

About Mads Barnkob

Electrician, programmer, experimenter and amateur scientist with experience in industry automation, programming and all kinds of high voltage generating electronics. Administrator of www.kaizerpowerelectronics.dk and the high voltage community forum www.highvoltageforum.net
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