Software Defined Radio (SDR) technology provides extreme flexibility in software control of radio parameters. However, because it is so different from traditional analog, mixer-based radio architectures, knowing how to optimally incorporate SDR into a commercial or military communications application requires something of a learning curve. To speed up the process, Analog devices and Avnet teamed up on an SDR kit that provides an assembled radio backplane using Analog Devices’ AD-FMCOMMS1-EBZFMC wireless communication module, application software, source code, and a number of evaluation tools.
The Zynq™-7000 SDR Kit (see figure) from Analog Devices consists of the Avnet ZedBoard 7020 motherboard; the communication module mezzanine card AD-FMCOMMS1-EBZFMC [which employs a field-programmable gate array (FPGA) from Xilinx (www.xilinx.com)]; model-based design kit from The MathWorks (www.mathworks.com); HDL source code; Linux drivers; Gerber files; reference projects; schematic diagrams; and a pair of MMCX to MMCX coaxial cables. The FMCOMMS1-EBZ includes an analog front end that can be quickly configured to work with a variety of computationally intensive FPGA-based applications. It is designed for use with the Xilinx Zynq® Software-Defined Radio Kit for complete flexibility in developing complete SDR-based communications products.
The SDR kit reduces risk and development time; it is suitable for wireless infrastructure as well as military and industrial radios. With a frequency band of 200 MHz, which can be tuned in a frequency band of 400 MHz to 4 GHz, it allows operators to bypass the RF section for baseband sampling. It is also well suited for multiple input multiple output (MIMO) antenna configurations. The SDR kit builds on the performance available from the AD-FMCOMMS1-EBZFMC, which is supplemented with a number of high-performance components from Analog Devices. These components include a 6-GHz model ADL5380 demodulator, a 6-GHz model ADL5375 modulator, a model AD9122 16-b digital-to-analog converter (DAC), and a model AD9643 14-b analog-to-digital converter (ADC).
The AD-FMCOMMS1-EBZFMC SDR board and mezzanine card operate with four functional partitions: signal transmission path, reception path, clock generation and management, and register access. For transmission, the card converts in-phase (I) and quadrature (Q) fundamental signals to modulated RF/microwave signals. The AD9122 interpolates this data and applies frequency translation to the baseband signals. A complex analog output from the AD9122 DAC then feeds a model ADL5375 quadrature modulator where it is converted to the required RF output frequency. After an image rejection filter, the signal is amplified by 20 dB by a model ADL5602 amplifier with a frequency bandwidth of 4 GHz. The amplifier provides RF outputs up to +7.5 dBm. Signals for the AD9122 DAC are generated either by an internal direct digital synthesizer (DDS) or by external memory.
When receiving a signal, the card converts the RF signal into complex I and Q components of the signal. The RF signal is demodulated by the model ADL5380 demodulator to achieve an intermediate frequency (IF) signal from 50 to 200 MHz. This I/Q IF signal is then filtered and fed to an AD8366 variable gain amplifier (VGA) that provides up to 15.75 dB of gain. After additional filtering, the signal is digitized with an AD9643 14-b ADC. The system can derive the clock signal from an on-board crystal or 50 MHz crystal oscillator or from an FPGA. Multiple boards can be kept in close synchronization for MIMO applications, provided the slave boards use the clock signals from the master board.
The Zynq-7000 SDR kit comes with operator manuals, software and guidelines to help the designer achieve the desired kit results. The kit includes the ISE{REG}Design Suite:WebPACK{TM} edition from Xilinx with a Chipscope Pro license node locked to the embedded Xilinx XC7Z020FPGA. The model-based design suite and evaluation tools from MathWorks help quickly move conceptual designs into working code for the SDR suite. The kit, which includes two Fourth Generation Long-Term Development (4G LTE) antennas for 2500 to 2700 MHz use for those operating in cellular systems, should certainly help speed up the educational process for any engineer interested in building an SDR architecture.
Analog Devices, Inc., 3 Technology Way, Norwood, MA 02062; www.analog.com, Avnet Electronics Marketing, 2211 S. 47th St., Phoenix, AZ 85034; (800) 408-8353, www.avnet.com.
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