Huawei RRU3908 base station circuit analysis (part 2 of 2)

The Huawei RRU3908 is an outdoor Radio Base Station with one to four carriers and one to six sectors at 20/40 Watt RF output power per carrier. Other teardowns of radio equipment can be found here.

Discussion of the teardown and analysis can be found here: https://highvoltageforum.net/index.php?topic=423.0

Central Processing Units

Network communication is handled by a Freescale MPC8321 PowerQUICC2 CPU. It runs at 200 MHz and has 2x 256 MB Hynix DDR2 RAM. It utilises a PMC QuadPHY 10 GB controller for the two optical input / output.

Decoding and encoding of the single bit streams for ADC and DAC are handled by the 3 Altera Cyclone III FPGA and the custom Huawei SD6151RBI controllers.

The single bit streams are treated by the Texas Instrument TMS320 series DSP CPUs. TMS320C6410 which is a fixed-point DSP that only calculates with integer numbers. TMS320CT16482 1 GHz DSP CPU calculates floating point numbers.

Huawei RRU3908 Receive part

The input signal comes in, two, out of phase lines and are first treated by a Skyworks SKY73021-11 1.7 to 2.2 GHz downconversion mixer. To get the frequency from 2.2 GHz to 550 MHz.

The local oscillator for the downconversion mixer is a Analog Devices ADF4110B.

A SIPAT SAW filter is used for isolation.

Depending on signal origin or type, I assume that the Analog Devices AD8376 Variable Gain Amplifiers are used before the signal lines split out into either a 3G ADC line or 4G ADC line.

The 3G line analog to digital conversion is handled by the Analog Devices AD6655-10 which is a 14-bit 150 MSPS chip that is specifically targeted for the 3G base stations.

The 4G line has a few more components as there is 2 MCL HSWA+1110 SPDT RF switches. These feeds into 2 Maxim MAX2039E up/downconversion mixers. An additional MCL HSWA+1110 SPDT RF switch it is handled by the Analog Devices AD9230-11-200 ADC which is a 11-bit 200 MSPS chip.

All timing is handled by the Analog devices AD9516-3. Which is a 14-output clock generator with a built in 2 GHz local oscillator.

Huawei RRU3908 Transmit part

The single bit datastream from the Altera Cyclone III FPGA is handled by 2 Analog Devices TxDAC AD9788 which are specified for 16-bit 800 MSPS.

To get the signal up in frequency to the broadcast carrier frequency 2 Analog Devices ADL5375-05 upconversion modulators are used. These has a range from 400 MHz to 6 GHz.

The signal is then sent through a 5 staged ceramic resonator band pass filter.

Signal phase can be switched from the setup of transistors and EMC Technology & Florida RF Labs HPJ2F hybrid couplers.

The pre-amplifier before the signal is sent to the power amplifier is a Freescale MMG3004NT1 high linearity amplifier capable of 17 dB amplification in the range of 400 MHz to 2.2 GHz.

To control the signal strength a MCL 31R5 digital step attenuator sits before the output connector. This is a 31.5 dB attenuator that can work in 0.5 dB steps from a 6-bit serial control interface.

Huawei RRU3908 Power Amplifier

The power amplifier uses two stages. Firstly a Infineon PTMA180402FL 40 Watt RF LDMOS. Secondly through a Xinger II XC1900A-03S hybrid coupler feeds two 90 degree out of phase signals to the output stage transistors which are NXP BLF6G20LS-140 140 Watt RF LDMOS.

The output is recombined in a Xinger II XC1900A-03S hybrid coupler before leaving to the diplexer through a circulator.