Nokia Siemens Flexi 3x70W FXEA 1800MHz Base Station Teardown: Power Amplifier

Nokia Siemens Flexi 3x70W FXEA 1800MHz Base Station Circuit Analysis (Part 2 of 3)

Circuit analysis of a Nokia Siemens Networks Flexi Multiradio base station. This have been in service as a 3 antenna system for mobile telecommunications. GSM/EDGE, WCDMA/HSPA and LTE capable. 3×70 Watt output power. Part 1 of the actual base station amplifier teardown can be seen here.

Power supply

The power supply is split into a input protection board and a main power supply board with three individual power supplies. One for each channel, controlled by a single Texas Instruments LM5035. Each power supply has a Analog Devices AD5241 256-step digital potentiometer to drive the gate driver ICs, through the GDTs to the IR5110 100V/61A MOSFET full-bridge. The output of the 48V to 48V center-tapped transformer is rectified with a B20200G 200V/10A Schottky diode and a large choke.


The main telecom protocol handling board with the 3 optical fiber in-/outputs has a NXP / Freescale MPC8377E 800 MHz PowerQUICC II CPU for the overall control. For the physical in-/outputs it has a Xilinx Spartan XC3S200A FPGA with a maximum of 248 user I/O. Single conditioning by Texas Instruments ACH973.

The three optical fiber interfaces is distributed to each their pair of a Texas Instruments TLK3131 1-channel 1Gbps transceivers. A Altera Hardcopy IV HC4E35LF1152NAH custom ASIC that handles the telecom protocol translations. To single bit stream for the DAC and conversion to telecom protocol from the single bit stream from the ADC.

Filter and diplexer

The connections from the diplexer passes through some 2-pole ceramic coaxial resonator blocks before entering a Macom MAATSS0015 15dB 4-bit digital attenuator. From here the receiving signal is going through down conversion in the Analog Devices AD5356 1200-2500 MHz Dual IF amplifier. Guessing from the Analog Devices AD8376 700 MHz +20dB Dual IF variable gain amplifier. The down conversion is from 1800 MHz to 700 MHz. There is two different ADC in place, perhaps for each their generation, like 3G and 4G. First to the right is a Analog Devices AD9255 14-bit 125 MSPS ADC. To the left is a Texas Instruments ADC16DV160 which is a dual 16-bit 160 MSPS ADC.

The transmitting signal only has a Analog Devices AD9122 dual 16-bit 1200 MSPS DAC. It has its up conversion through a Analog Devices ADL5375 0.4-6 GHz Quadrature IF modulator. From here going through a 8-pole ceramic coaxial resonator block and being fed into the power amplifier.

Associated functions for clock generation and power supply is handled by Analog Devices ADF4106 6 GHz PLL frequency synthesizer, Analog Devices ADM660 CMOS switched capacitor voltage converter and Texas Instruments PT77701 1.8V ultra fast regulator.

The tuner board has feedback from the amplifier and diplexer on reflected energy and received signals. The information is handled by a NXP / Freescale MCF5208 Coldfire RISC CPU with built-in SRAM, DDR SDRAM, DMA controller and 10/100 Mbps Ethernet interface. The tuning motors are controlled individually for each of the three sectors, by a Lattice LCMX0640 FPGA/CPLD hybrid. The motor drivers have a on-board separated power supply from the 48VDC used for radio circuits.

RF power amplifier

The power amplifier module sits on a aluminium silicon carbide base plate and has the power transistors mounted directly on this. The pre-amplifier IC is a NXP / Freescale MW7IC2040N with a 4 Watt output power at 1805-1880 MHz. Anaren Xinger 1P503S 3 dB hybrid couplers are used for the 90 degree phase split. Thereby going into the Doherty amplifiers built on two Ampleon BLF720LS-250P LDMOS. Which can put out 250 Watt at 1805-1880 MHz. The output combiner is a Anaren Xinger II XC1900E-03S 3dB hybrid coupler before going to off-board circulator that protects the amplifier module from the reflected energy from the antenna, which are measured through a direct coupler at the top of the board.

The diplexer has three identical sets of resonant cavities, it is designed with 5-pole filters for the receiving part and 6-pole filter for the transmitting part, with a lot of added couplings between the cavities.

At last, this is how you configure a super sophisticated 4G base station amplifier, a single resistor to select between 1800 or 1900 MHz carrier frequency.

Mads Barnkob

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

View all posts by Mads Barnkob →

Leave a Reply

Your email address will not be published.