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.
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.