How to Choose the Right Oscillator in 5 Steps

A 5-Step Oscillator Selection Method

Choosing the right frequency reference is a trade-off between five requirements. Work through them in order — each step narrows the candidate family until one model remains.

Step 1: Decide the Holdover Budget

Holdover is how long the system stays accurate without an external reference. Ask: what is the maximum allowed time error after GNSS/PTP loss, and for how long? < 1 μs over 24 h requires a disciplined oscillator or rubidium; < 100 μs over 24 h can be met by a good OCXO; ±0.1 ppm over the product life is TCXO territory.

Step 2: Specify the Phase Noise You Actually Need

Phase noise matters most for RF synthesizers, radars and high-speed serial links. Look up the phase noise at the offset frequency that matters (usually 100 Hz, 1 kHz or 10 kHz). A telecom card needs -140 dBc/Hz @1 kHz; a coherent radar needs -165 dBc/Hz or better. Matching the oscillator's phase noise to your receiver's floor avoids paying for performance you will never use.

Step 3: Power and Board Size

OCXOs draw 0.3–1.5 W and warm up in minutes. GPSDOs draw 1–2 W. Rubidium draws ~15 W. CSACs draw 0.13 W but cost more. Battery-powered or thermally constrained designs push you toward TCXO, micro-disciplined (KDO9/KDO5) or CSAC.

Step 4: Operating Temperature and Vibration

Commercial electronics: -20 to +70 °C. Outdoor base stations and substations: -40 to +85 °C. Aerospace and defense: -55 to +125 °C plus vibration. Vibration selects the G-sensitivity spec: stationary lab ≤1E-10/g, moving platform ≤1E-11/g, launch-rated ≤5E-11/g (KOR series).

Step 5: Fit the Budget and Lead Time

A TCXO is tens of dollars; an OCXO is hundreds; a rubidium or CSAC is thousands. Western-brand lead times often stretch to 16–26 weeks; KCCS standard models ship in 6–10 weeks, custom in 8–16. If your program cannot absorb a redesign, ask for a pin-compatible second source.

Quick-Start Cheat Sheet