Summer 2008 Vol. 17, No. 2
Model 7141-420 Transceiver with Dual Wideband DDC and Interpolation Filter Installed Cores
- Installed Core 420, two high-performance wideband DDCs and interpolation filter, installed
- Extended DDC decimation range of 2 to 1,048,576 and bandwidth range of 40 MHz to 76.3 Hz
- Extended DUC interpolation range of 2 to 32,768 and bandwidth range of 40 MHz to 2.44 kHz
- Two 125 MHz A/Ds and two 500 MHz D/As included
- LVDS clock/sync bus for multimodule synchronization
- Also available in PCI and cPCI formats
Model 7141-420, Dual Digital Transceiver with Wideband DDC and Interpolation Filter cores, is a complete software radio system in PMC/XMC format. It includes two A/D and two D/A converters for connecting to HF or IF ports of a communications or radar system.
The 7141-420 receiver section features two LTC2255 125 MHz 14-bit A/D converters and one TI GC4016 quad multiband digital downconverter. The digital outputs of the A/Ds are delivered to the Virtex-II Pro FPGA and to other module resources including the GC4016 which supports a decimation range from 32 to 16,384. For an A/D sample clock frequency of 100 MHz, the output bandwidth for each of the four channels ranges from 2.5 MHz down to 5 kHz. By combining two or four channels, decimations of 16 or 8 can be achieved for an output bandwidth of up to 5 or 10 MHz, respectively.
For applications that require even wider bandwidths, the module includes Pentek's installed core 420 high-performance wideband DDC, similar in functionality to the GC1012 but with enhanced performance, and an interpolation filter that extends the range of the DAC5686 D/A converter.
Core 420 Wideband Downconverter
Like the GC4016, the Core 420 downconverter translates any frequency band within the input bandwidth range down to zero frequency. A complex FIR low pass filter then removes any out of band frequency components. An output decimator and formatter deliver output data in either real or complex representation.
An input gain block scales both I and Q data streams by a 16-bit gain term. The NCO provides over 118 dB spurious-free dynamic range (SFDR).
The mixer utilizes four 18x18-bit multipliers to handle the complex inputs from the NCO and the complex data input samples. The FIR filter is capable of storing and utilizing up to four independent sets of 18-bit coefficients for each decimation value. These coefficients are user-programmable using RAM structures within the FPGA.
Two identical Core 420 DDCs are factory installed in the 7141-420 FPGA. The decimation settings of 2, 4, 8, 16, 32, and 64 provide output bandwidths from 40 MHz down to 1.25 MHz for an A/D sampling rate of 100 MHz. It also delivers better stopband rejection than the GC4016 in combined channel modes.
A multiplexer in front of the Core 420 DDCs allows data to be sourced from either the A/D converters or from the output of the GC4016, extending the maximum cascaded decimation factor to 1,048,576.
Core 420 Interpolation Filter
The interpolation filter included in the 420 Core, expands the interpolation factor from 2 to 32,768 programmable in steps of 2, and relieves the host processor from performing upsampling tasks. Including the DUC, the maximum interpolation factor is 32,768 which is comparable to the maximum decimation of the GC4016 narrowband DDC.
All the standard features are retained including D/A waveform generation, data routing and formatting, and transient capture.
Performance characteristics are included at the end of this issue. For more information and price quotations on the Model 7141-420 commercial and rugged versions, go to: click here.