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Microstepper

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Last edited by Anders Wallin
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Microstepper

Project Description

High-resolution frequency/phase-microstepper for timing laboratories. This is a frequency synthesizer used with atomic clocks for generation of time-scales. The frequency input is from a free-running clock, and the output frequency is adjustable at 1e-17 fractional frequency or lower level.

Motivation: active Hydrogen maser atomic clocks used for time-scales typically show linear frequency drift in the range of (fractional frequency) 1e-15 to 1e-16 per day. Ceasium clocks on the other hand usually do not show frequency drift, but the output frequency differs from the SI-second by a few nanoseconds per day, corresponding to a fractional frequency of a few 1e-14. To maintain a time-scale the microstepper is used to correct for the estimated frequency offset and drift of the free running clock. Conventional signal generators/synthesizers usually have a resolution of 1e-12 only - so they only suffice to adjust frequency in ~100 ns/day steps - hence we need a fine resolution frequency offset generator, the microstepper.

See Block-diagram for a discussion of the operation and resolution of the microstepper.

Main Features

  • Frequency input: a free-running 100 MHz (alternatively 5 or 10 MHz, not tested) clock
  • Output frequency adjustable at 1e-17 fractional frequency or lower level
    • frequency output 100/10/5 MHz
    • 1 pulse-per-second (1PPS) output
  • Controllable over Ethernet
  • Built up out of several boards
    • DDS-board, produces programmable LO-signals based on a reference frequency input.
    • MIXER-board, compares reference-clock to OCXO and produces a phase-detector output for locking the OCXO
    • OCXO-board, provides frequency output (and dividers) of the microstepper.
    • PICDIV-board, produces 1PPS signal based on 10 MHz input.
  • Licenced under CERN-OHL-S V2
  • Designed with KiCAD

References

  • G. D. Rovera, M. Abgrall, M. Siccardi, "Characterization of an Auxiliary offset Generator for steering of H Masers", 2012, 10.1109/EFTF.2012.6502322
  • F.G. Ascarrunz, "A high resolution phase and frequency offset generator", 1998, 10.1109/FREQ.1998.717932
  • US6278330B1 (expired), Franklin G. Ascarrunz "Frequency and phase offset signal generator and method"
  • US4358741A (expired), Roy Nardin, "Micro time and phase stepper"
  • US4417352A (expired), Leonard F. Shepard, "Microphase stepper employing improved digital timing incrementer employing a rate multiplier"

Users

  • VTT MIKES UTC-laboratory, Finland

Contributions to KiCad libraries

  • OH300-series OCXO symbol 1174
  • AD630 symbol 1279
  • MC12080 symbol 1283
  • 74AHC1G4210 symbol 1282
  • MC12090 symbol 1280
  • AD9912 symbol 1655
  • OPA188 symbol 1310

Contacts

Design and general questions

Commercial producers

  • Not commercially available yet

Status

Date Event
2020-06-02 DDS-board draft design
2020-01-03 First prototype has been running in the lab for months.
2019-02 Experiments with AD9912 resolution (47 bits!)