Arcetri Radioastronomy Group

Digital Receiver for the Uniboard Project

The Uniboard is a general purpose digital processing board, hosting 8 large field programmable gate arrays (Altera EPS4GX230), 16 10G optical links and optional DDR3 memory banks.

It has been developed basically as a building block for future VLBI correlators, but can be used for a number of other applications, including adaptive beamforming, pulsar dedispersion, RFI identification and suppression.

Uniboard top side (click to enlarge)

Here at Arcetri we are studying its use as a wideband digital receiver. The receiver characteristics are:

  • Maximum instantaneous bandwidth of 4 GHz (8 GS/s)
  • Input quantization of 6-8 bits/sample
  • Up to 64 output sub-bands, independently tunable over the input band
  • Bandwidth of each sub-band selectable from 1 to 128 MHz
  • Output format: VDIF, real samples with 1, 2, 4, 8 bit quantization
  • Output connection: UDP jumbo packets (one packet per VDIF frame) over 10G IP links
    • Receiver architecture is based on a parallel polyphase filter bank, dividing the input band into 32 overlapping bands of 256 MHz each. Tunable filters then extract the output bandwidths from a selection of these bands.

    Simulation of the polyphase FFT filterbank. Input signal is a sinewave sweeping the entire 4 GHz band. Outputs are given for channels 0, 1, 15, 8, 16, 17, 30, 24, 31 (top panel) and 2, 3, 13, 14, 17, 18, 28, 29 (bottom panel)

    A separate version with 1 GHz bandwidth has also been developed. This version fits nicely in a single FPGA, so 4 independent bands can be analyzed in 4 FPGAS leaving the other 4 for other purposes (spectropolarimetry, pulsar dedispersion, RFI mitigation).

    1 GHz bandwidth splitted into 16 64 MHz subchannels. Top 9 graphic tracks are the 9 outputs from the polyphase FFT. Bottom 16 tracks are the outputs of individual sub-channels (0 to 15). Channel 10 has been programmed for a 32 MHz bandwidth.

    Documentation

  • Uniboard Digital Receiver - Initial design document; G. Comoretto, A. Russo, G. Tuccari, A. Baudry, P. Camino, B. Quertier [pdf]
  • Uniboard Digital Receiver Programming Manual; G. Comoretto, A. Russo, G. Tuccari, A. Baudry, P. Camino, B. Quertier [pdf]

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