There are a number of problems to address when processing high bandwidth signals in real time. One of these is the actual data processing speed another is the other is the speed of data communications. The AstroFFT Digital Spectrometer System makes use of the latest generation of Field Programmable Gate Arrays (FPGA's) to perform the real time data processing required. In the case of each AstroFFT processing engine, the input data enters at a rate of about 200 MBytes per second and the 4096 point, 14 bit, FFT algorithm together with power calculation and integration needs to be performed within 86 microseconds.
The processing engine has two analogue signal inputs and one digital
clock input. A large number of digital I/O lines are available for interconnecting
FPGA engines or for other purposes. Each analogue signal is passed through
a low pass anti-aliasing filter to a fast 14 bit analogue to digital convertor.
The digital signal streams from both analogue to digital convertors are
passed through a "glue logic" FPGA to the main processing FPGA. In the
case of the AstroFFT system the "glue logic" FPGA's function is to provide
master clock selection and remove DC offset from the analogue to digital
conversion stages. There are a large number of free gates within this FPGA
that could be used to pre-process the data in other ways.
The main processing FPGA is loaded with appropriate "core" firmware
to provide the required algorithm. The current supplied algorithms include:
Analogue Mode
The average power of the signal and number of full scale readings are calculated and this information together with the digital signal stream data is sent directly to the host. As the host is unable to keep up with the full data rate, sets of 4096 samples are processed and sent to the host on request.FFT Mode
A a single digital stream is processed by a 4096 point, 14 bit FFT algorithm and the power of the resulting frequency spectra are integrated over time. The integrated frequency spectra are sent to the host every 0.1 seconds (programmable).QFFT Mode
Quadrature FFT mode. The input signals are in quadrature with each other. In this mode one digital stream is sent to the real data inputs and the other data stream is sent to the imaginary inputs of a 4096 point, 14 bit FFT algorithm. The power of the resulting frequency spectra are integrated over time. The integrated frequency spectra are sent to the host every 0.1 seconds (programmable).
https://portal.beam.ltd.uk/support/astrofft
Beam Ltd | http://www.beam.ltd.uk | Tel:  01454 324512 |
Alpha Data | http://www.alphadata.co.uk |   | Bristol University | http://www.star.bris.ac.uk/coldrick.html |   |