A General Purpose Spectrometer for a Feedhorn Array Receiver,
Paper 2541John Ford , Jason RayNational Radio Astronomy
Observatory, PO Box 2, Green Bank, WV 24944,
[email protected]@nrao.edu
Reconfigurable Open Architecture Computing Hardware (ROACH
board
AbstractWe present the conceptual design for a general-purpose
spectrometer system designed to support the Green Bank Telescope
(GBT) K band Focal Plane Array (KFPA) project. This design is based
on use of reconfigurable computing elements and supporting design
tools designed by the Center for Astronomy Signal Processing and
Electronics Research (CASPER) at the University of California at
Berkeley and collaborators. The CASPER toolset and hardware
platforms provide a standard interface to the signal processing
power available in today's Field Programmable Gate Array (FPGA)
devices. This paper presents an analysis of the projected cost and
performancetradeoffs, physical size and weight, and time to deploy
for a spectrometer system supporting a seven pixel, dual
polarization array receiver, and extends that analysis to a 61
pixel dual polarization receiver. The analysis includes the entire
data stream, from digitizer to disk.iADC-2Basic Spectrometer
Requirements for GBTWide band modes for searchingMultiple narrow
band modes for detailed analysis of spectral linesExisting
Spectrometer modes (Subset of some 800 possible modes)16 * 50 MHz
BW, 16K spectral channels/IF8 * 200 MHz BW, 8K spectral
channels/IF8 * 800 MHz BW, 2K spectral channels/IFThe GBT K band
Feedhorn Array 7 Pixels, 18 to 26.5 GHz8 GHz RF BandwidthDual
Polarizations1.8 GHz IF BandwidthExpansion plans for up to 60
pixelsiADC2ROACH/ROACH-2Reconfigurable Compute
EngineROACH/ROACH-2Reconfigurable Compute
EngineiADC2ROACH/ROACH-2Reconfigurable Compute Engine10 GbE
switchBackend data storage computerFiber to LabDigitizersFFT
enginesSignal Combiner/AccumulatorPer-Pixel HardwareShared
HardwareIF ConnectionsSampling clock, 1PPS Basic Spectrometer
System Design ParametersNew GBT Spectrometer Minimum
Specifications14 IF channels800 MHz bandwidth32K spectral channels
per IF10 ms minimum dump time (4 bins, using cal and sig/ref
signalling) 16 simultaneous 50 MHz sub-bands across the 32K
channelsCross products within each pixel's IF
ConfigurationPixelsIF'sFFT Channels/IFBandwidthSub-bandsCompute
EnginesADC'sCoresDisk BandwidthHardware CostPower ConsumptionSize
and WeightGBT Spectrometer, wideband mode482048800 MHz116
correlator boards8112 MB/S~ $1M7 KW140 U, 500 KgBasic K band FPA
spectrometer71432K2.0 GHz1621 ROACH boards14875 MB/S~$200K3 KW31 U,
150 KgExpanded K band FPA Spectrometer6012032K8 GHz16600 ROACH
boards24016321 MB/S~$3.8M45 KW650 U, ???? KgExpanded W band FPA
Spectrometer10020032K8 GHz161000 ROACH boards400321071 MB/S~$6.8M75
KW1050 U, ???? Kg
