Contents
What is an OCXO?
An oven-controlled crystal oscillator (OCXO) keeps the quartz resonator at a fixed elevated temperature so that ambient changes have minimal effect. Compared with TCXOs, OCXOs achieve much tighter frequency stability and excellent short-term noise—ideal for network timing, precision measurement, and holdover.
For a wider taxonomy of timing devices, see our product overview: Timing Devices (TCXO, VCXO, OCXO).
Quick pick: OCXO vs TCXO vs Rubidium
- OCXO: Best short-term stability (ppb-level) and phase noise for SyncE/PTP, T&M; needs warm-up and more power.
- TCXO: Smaller, lower power (ppm-level stability); great for GNSS modules, mobile, and embedded clocks.
- Rubidium: Superior long-term holdover; higher cost/power/complexity. Pair with GNSS disciplining where necessary.
How to choose the right OCXO
Stability (ppb)
Match your worst-case frequency error budget (packet clocks, PLL references, frequency standards). Single-digit ppb is typical for high-grade OCXOs.
Match your worst-case frequency error budget (packet clocks, PLL references, frequency standards). Single-digit ppb is typical for high-grade OCXOs.
Phase noise / Jitter
Telecom and high-speed links benefit from very low phase noise. Pay attention to 10 Hz–10 kHz offsets for PLL references.
Telecom and high-speed links benefit from very low phase noise. Pay attention to 10 Hz–10 kHz offsets for PLL references.
Warm-up & Power
Ovens need time and power to reach set-point. Ensure your system can accommodate warm-up and steady-state thermal load.
Ovens need time and power to reach set-point. Ensure your system can accommodate warm-up and steady-state thermal load.
Crystal Cut
SC-cut offers lower g-sensitivity and better stability than AT-cut; preferred in demanding telecom and T&M scenarios.
SC-cut offers lower g-sensitivity and better stability than AT-cut; preferred in demanding telecom and T&M scenarios.
Output Type
Choose HCMOS for simple digital loads or sine-wave for low-noise RF chains / long traces.
Choose HCMOS for simple digital loads or sine-wave for low-noise RF chains / long traces.
Form Factor
From compact SMD cans to larger SC-cut modules—balance PCB area vs. performance & power.
From compact SMD cans to larger SC-cut modules—balance PCB area vs. performance & power.
FCom OCXO model comparison
The table below summarizes stability, phase noise, package, and outputs across FCom OCXO families to help you shortlist by application.
| Model | Key Strength | Typical Stability | Phase Noise (best case) | Package (approx.) | Output | Supply | Recommended Uses |
|---|---|---|---|---|---|---|---|
| FOC-4D (SC-cut) | Ultra-stable, low g-sensitivity | ±5 ppb class* | Very low* | 36.3×27.2 mm | HCMOS / sine (options) | 3.3 V / 5.0 V (options) | Test & measurement, frequency standards, core network timing |
| FOC-5S-LN | Ultra-low phase noise in a small form factor | ±10 ppb* | to −160 dBc/Hz* | 14.7×9.6×8.2 mm | HCMOS / sine (options) | 3.3 V | PTP 1588 holdover, wireless base stations, optical transport |
| FOC-6S | Balanced SMD OCXO | ±10 ppb* | to −150 dBc/Hz* | 25.4×22.1×11.0 mm | HCMOS | 3.3 V (5.0 V opt.) | SDH/SONET, digital switching, synthesizers, general timing |
| FOC-1D | Compact metal-can OCXO | ±0.1 ppm (±100 ppb)* | Low* | 20.3×12.7 mm | HCMOS | 3.3 V / 5.0 V (options) | Industrial timing, legacy replacements, space-constrained designs |
| FOC-5S | Balanced low-noise OCXO (standard) | ±10 ppb* | Low* | Compact SMD* | HCMOS / sine (options) | 3.3 V | PTP 1588, wireless, optical transport |
| FOC-2D | General-purpose OCXO family | ppb-class* | Low* | Metal can / SMD* | HCMOS / sine (options) | 3.3 V / 5.0 V (options)* | Industrial timing, baseband clocks, replacements |
| FOC-3D | Mid-size OCXO family | ppb-class* | Low* | Metal can / SMD* | HCMOS / sine (options) | 3.3 V / 5.0 V (options)* | Test & measurement, switching, synthesizers |
| FOC-7S | High-performance SMD OCXO | ppb-class* | Low* | SMD* | HCMOS / sine (options)* | 3.3 V (5.0 V opt.)* | Telecom timing, SyncE, PTP |
* Family-level capabilities; please review each model’s datasheet for guaranteed specifications.
Applications & on-site case notes
From our customer projects and internal evaluations, here’s how engineers typically map OCXO choices:
- PTP 1588 / 5G base stations: FOC-5S-LN for very low phase noise and stable holdover.
- Core/metro transport (SDH/SONET), digital switching: FOC-6S as a balanced SMD option.
- Test & measurement / frequency standards: FOC-4D (SC-cut) for ultra-stable references.
- Industrial timing modules / retrofits: FOC-1D where compact cans and moderate power are desired.
Explore related reading on our site: What Are Timing Devices? · TCXO vs OCXO · Oscillator Electronics Applications
Product examples (ready-to-use scenarios)
Common reference configurations for fast prototyping. Always validate against the datasheet and your system’s temperature, power-up, and jitter budgets.
FOC-5S-LN — compact ultra-low-noise OCXO
- 5G / 1588 Grandmaster holdover: 10 MHz (sine or HCMOS); target stability ≤±10 ppb (system budget). Allow 60–120 s warm-up. 3.3 V supply; use LDO + LC filtering; place 10 µF + 0.1 µF decoupling close to pins. Request this configuration
- OTN / SerDes reference: 25 MHz (HCMOS); end-to-end jitter budget ≤1 ps RMS; keep traces short with single-point ground. For long runs, consider sine output to reduce reflections. Model page
FOC-4D — SC-cut ultra-stable reference
- Lab / production 10 MHz standard: Sine output driving synthesizers/metrology gear; isolate from airflow and vibration; shield can and soft mounts recommended. Model page
- Core network PRC / PRS sync: 10 or 20 MHz (sine); SC-cut lowers g-sensitivity and improves aging for long-term holdover. Request this configuration
FOC-6S — balanced SMD OCXO
- SDH/SONET side-chain clock: 19.44 MHz (HCMOS); add proper terminations near board edge; match return paths; aim <10 mVpp supply ripple. Model page
- PTP boundary clock: 10 MHz (HCMOS) with temperature-aware calibration for short-term holdover and fast relock. Request this configuration
FOC-1D — compact metal-can OCXO
- Industrial DAQ master reference: 10 MHz (HCMOS); 3.3/5.0 V options; metal can aids grounding/shielding—great for space-constrained retrofits. Model page
- Embedded module replacement: 20 MHz (HCMOS) drop-in with improved ppb-class stability across temperature. Request this configuration
FOC-2D — general-purpose OCXO family
- Cost-optimized GPSDO: 10 MHz (sine) combined with GNSS disciplining for balanced holdover vs. BOM. Model page
- Microwave backhaul endpoint: 20 MHz (sine); use controlled-impedance routing and proper terminations for long traces. Request this configuration
FOC-3D — mid-size OCXO family
- Digital switching / private line: 19.44 MHz (HCMOS); good stability with moderate power and size. Model page
- Synthesizer reference: 10 MHz (sine); better short-term noise than typical TCXOs—helps overall phase-noise budget. Request this configuration
FOC-7S — high-performance SMD OCXO
- SyncE / packet-network timing: 19.44 or 10 MHz (HCMOS/sine) for switching/routing cards; check airflow and thermal coupling. Model page
- 5G RAN frequency reference: 30.72 MHz (HCMOS); common basestation clock tree rate; choose drive strength per trace length/crosstalk. Request this configuration
Tip: for 156.25/312.5 MHz Ethernet rates, generate those via synthesis/multiplication from a clean OCXO (10/20/25/30.72/19.44 MHz) to balance phase noise and jitter.
Design tips
- Power & warm-up: Budget oven warm-up (seconds → minutes) and steady-state power. Use staged start-up if inrush matters.
- Airflow & placement: Avoid drafts and hot spots to reduce oven workload.
- Supply hygiene: Decouple close to pins; consider LDO + LC filtering for low noise.
- Vibration / g-sensitivity: Prefer SC-cut (e.g., FOC-4D) and keep away from vibration sources.
- Output routing: For sine, use controlled impedance and proper terminations. For HCMOS, watch edge rates and fan-out.
FAQ
What’s the difference between OCXO stability in ppb and ppm?
1 ppm = 1000 ppb. High-grade OCXOs are often specified in single-digit ppb, which is 100–1000× tighter than typical ppm-class oscillators.
Can an OCXO run at −40~+85 °C?
Yes, many OCXOs support industrial temperatures. Power rises at low ambient temperatures as the oven works harder; ensure thermal and power budgets account for this.
How should I plan for holdover?
Combine a low-drift OCXO (e.g., FOC-5S-LN or FOC-4D) with robust PLL/clock-recovery algorithms and temperature-aware calibration. Validate over mission profiles.
Which output should I order?
Use HCMOS for logic-level loads and cost efficiency. Choose sine-wave where low analog/RF noise and long trace runs are priorities.
OCXO vs rubidium—when to choose which?
Rubidium standards provide superior long-term stability and holdover but at higher cost, power, and system complexity. For many SyncE/PTP boundary clocks and base-station designs, a high-grade OCXO with GNSS disciplining is sufficient.
How does oven set-point temperature affect power and performance?
Higher set-points can improve short-term stability and reduce sensitivity to ambient swings, but they increase warm-up time and steady-state power. Choose a set-point that balances performance with your thermal budget.
If you need TCXO guidance for GNSS timing modules, see our application note: TCXO for GPS/GNSS Applications.
