KCCS
Precision Timing
A practical comparison of the four precision timing architectures, with decision rules for holdover, power and cost.
When an engineer sits down to choose a precision frequency reference, the real choice is rarely "OCXO or TCXO" — it is which of four architectures meets the holdover, power, cost and size budget. The table below summarizes the four KCCS families; the sections that follow explain the trade-offs.
| Architecture | Stability (ADEV) | Holdover | Power | Cost | Best When |
|---|---|---|---|---|---|
| OCXO | 8E-14 @10s | Free-run, hours of sub-μs | 0.3–1.5 W | $ | Stable reference always on, no GNSS needed |
| GPSDO / Disciplined | 1E-12 @1s (locked) | ±1.5 μs/24h | 1–2 W | $$ | Need UTC traceability, GNSS available |
| Rubidium | 1E-11/day aging | <0.1 μs/day free-run | ~15 W warm-up | $$$ | No GNSS, long holdover, lab/grandmaster |
| CSAC / CPT | 3E-11/100s | ≤1 μs/24h | 0.13 W (CSAC) | $$$$ | Battery-powered, no warm-up, compact |
The oven-controlled crystal oscillator keeps the crystal at a temperature where its frequency is least sensitive to ambient changes. It has the lowest close-in phase noise of any practical oscillator (down to -170 dBc/Hz @1 kHz in our KON series) and the best Allan deviation (8E-14 @10s in KOS). The price is steady power draw and warm-up time (3–15 minutes). Choose an OCXO when the equipment is always powered on and the reference does not need to self-calibrate against a GNSS or 1PPS signal.
A GPSDO (also called a disciplined oscillator) uses the 1PPS pulse from GNSS to continuously steer an internal OCXO. While locked, it holds microsecond-or-better accuracy to UTC; when the satellite signal disappears (jamming, urban canyon, indoor), it "holds over" on the OCXO's calibrated frequency. KCCS KDO families hold ±1.5 μs over 24 hours — enough for PTP grandmasters, substation PMUs and 5G base stations. The GPSDO is the right answer whenever you need UTC traceability but cannot afford a rubidium.
A rubidium frequency standard locks its output to the hyperfine transition of rubidium-87. It ages at roughly 1E-11 per month and holds sub-microsecond accuracy for days without any external reference. Warm-up is a few minutes and power draw is ~15 W. Choose rubidium when GNSS is unreliable, when the equipment must survive long GNSS outages, or when it is itself a lab or grandmaster reference.
The chip-scale atomic clock (CSAC) miniaturizes the rubidium physics onto a chip-scale vapor cell, consuming just 130 mW. It does not match the phase noise of an OCXO but delivers atomic-level holdover (≤3E-11/100s) with no warm-up time. It is the right choice for battery-powered nodes, unmanned sensors, and equipment that must be accurate from instant power-on.