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Distributed Direct Digital Synthesis over White Rabbit D3S
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Rf distribution demo

Last edited by Tomasz Wlostowski Jan 20, 2016
Page history

RF distribution demo (the first attempt)

Note: this is page describes the very first attempt at RF distribution over Ethernet, done in 2013. This system is no longer developed.

Specification

  • Default frequency: 10 MHz (LHC bunch clock). Can be reprogrammed to 1-70 MHz.
  • Single master node sending to single slave node.
  • Hardware: a DDS mezzanine hosted on a SPEC FMC carrier and a White Rabbit switch.

The design

Clocks:*

  • Everything except the DAC is clocked with 125 MHz WR clock, coming from the FMC (not the SPEC local oscillator).
  • The DAC is driven with a 500 MHz clock, in-phase with the 125 MHz WR reference.

DDS core:*

  • Lookup table-based DDS with configurable resolution & tuning word width.
  • LUT interpolation and dithering - no spurs in the output (~90 dB SFDR).
  • Output sample rate: 500 MSPS, tuning words are delivered synchronously to WR clock and interpolated
    4 times.

DDS PLL:*

  • Locks the phase of the DDS numerically controlled oscillator to the phase of the RF input signal.
  • Analog phase detector (ADF4002) followed by a simple antialiasing filter and a 16-bit 1MSPS ADC
  • The true loop filter is digital (a simple PI controller for the moment).
  • The loop filter works at 1/1024 of the WR clock rate (~122 kHz) to reduce the amount of data samples to send. Interpolation is done with a CIC (cascaded integrator-comb) filter.
  • Corrections wrs the baseline frequency are added to the DDS.

Data streaming:*

  • Correction values are timestamped and sent over Ethernet (through the streamers from the WR tutorial).
  • Received corrections are "executed" after a fixed delay (set to 20 us for the moment).
  • Point-to-point only for the moment, MAC addresses are fixed.

Useful documentation:

Tom's PH-ESE Demo presentation - contains also preliminary measurements

ToDo:

  • Properly calculate the PLL filter.
  • Phase compensation (currently the slave can recover only frequency).
  • Compression/prediction of correction values and/or adaptive interpolation ratio. Currently used fixed update rate of 122 kHz causes a lot of network traffic.
  • Fix mezzanine's issues.

Files

  • rf_block.jpg
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  • Documents
  • Home
  • Rf distribution demo
  • Setup cern vme
  • Faq
  • Documents
    • 2013 demo presentation in ph ese
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