Do I need 26 MHz or 16.368 MHz for my GNSS?

26 MHz is common for RF SoCs and supports tight channel spacing; 16.368 MHz may align with specific basebands. Match the reference frequency and tolerance to your receiver’s PLL plan and Doppler search window.

CMOS vs clipped-sine output?

CMOS simplifies digital domains but can add switching noise; clipped-sine reduces EMI and can improve reciprocal mixing. Follow the RF front-end input recommendations.

What about Allan deviation and g-sensitivity?

Low Allan deviation reduces short-term wander in the carrier loop; low g-sensitivity helps in high-dynamic platforms (UAVs, automotive) to prevent microphonic-induced jitter.

Automotive qualification?

For automotive GNSS, consider AEC-Q200 variants and extended temperature ranges (e.g., −40~+105 °C) with documented aging and shock performance.

TCXO for GNSS Timing Guide-Fuji Crystal (Hong Kong) Electronics Co., Ltd.

Why Stable Timing Matters for GNSS Systems

Global Navigation Satellite Systems (GNSS)—including GPS, GLONASS, Galileo, and BeiDou—rely on precise frequency sources to ensure signal synchronization and sub-meter location accuracy. Instability or drift in a reference (e.g., TCXO) degrades Time To First Fix (TTFF), widens the Doppler search window, and reduces code/carrier correlation, especially in urban canyons, weak-signal, or high-dynamics scenarios.

How TCXO Ensures GNSS Synchronization

GNSS receivers down-convert satellite signals and maintain alignment between internal timing loops and satellite clocks. A TCXO with tight frequency stability and low phase noise reduces carrier frequency error during acquisition/tracking and narrows PLL/FLL search space.

Stable reference during cold start and wide temperature swings (−40~+85 °C).
Narrower Doppler search window → lower CPU load and faster GPS lock time.
Fewer false locks, better SNR in weak-signal conditions; improved reacquisition after fades.

TTFF Performance with Different TCXO Grades

Representative TTFF outcomes (typical conditions) based on vendor documentation such as u-blox GNSS receiver specs:

TCXO Accuracy	Cold Start TTFF	Warm Start TTFF	Reacquisition
±0.5 ppm	~28 s	~5 s	<1 s
±2.5 ppm	~37–42 s	~9 s	2–4 s
No TCXO	>50 s	>12 s	3–8 s

Conclusion: Using a ±2.0 ppm or better TCXO (e.g., 26 MHz) reduces time-to-lock and improves robustness under intermittent satellite visibility.

References: u-blox Application Note “GPS Performance vs. TCXO Characteristics” (UBX-13003158), NEO-M9N Hardware Integration Manual.

Recommended Frequency Parameters for GNSS TCXO Design

Parameter	Recommended Range
Frequency Stability	±0.5 to ±2.0 ppm
Initial Frequency Tol.	±1.0 ppm @ +25 °C
Temperature Range	−40 °C to +85 °C
Phase Noise @10 kHz	≤ −145 dBc/Hz (application-dependent mask)
Aging (First Year)	≤ ±1.0 ppm
Output Type	CMOS / Clipped-Sine (select to match RF/SoC)

Design Checklist & Integration Tips

Reference Frequency & Load

Common GNSS refs: 26 MHz, 16.368 MHz, 38.4 MHz.
Match load capacitance (CL) & input spec of RF/MCU.
Verify ESR & drive level to ensure fast startup.

Noise & Stability

Low close-in phase noise reduces reciprocal mixing; check RMS jitter (12 kHz–20 MHz).
Track Allan deviation for short-term stability and wander.
Target aging ≤ ±1 ppm/year; consider g-sensitivity for high-dynamic platforms.

Output & Power

CMOS for direct digital domains; clipped-sine for low-EMI analog paths.
Check supply (e.g., 1.8/2.8/3.3 V) and current budget for always-on domains.
Automotive? Consider AEC-Q200 qualified parts and −40~+105 °C variants.

For network synchronization and holdover architectures, see Telecom & 5G timing (PTP/SyncE). For deterministic motion control and TSN in factories, refer to Industrial Automation & Robotics timing.

FVT Series TCXOs for GNSS Devices

Specialized models for positioning systems:

FVT-2S — Compact 2.5×2.0 mm for wearables & portable GNSS.
FVT-3S — 3.2×2.5 mm for automotive/industrial receivers.
FVT-6S — Ultra-mini 2.0×1.6 mm for lightweight GPS designs.
FVT-5S — CMOS/Clipped-Sine dual outputs for flexibility.
FVT-7S — Wider frequency range with low jitter.

Explore More from Fuji Crystal

FAQ

Do I need 26 MHz or 16.368 MHz for my GNSS?: 26 MHz is common for RF SoCs and supports tight channel spacing; 16.368 MHz may align with specific basebands. Match the reference frequency and tolerance to your receiver’s PLL plan and Doppler search window.
CMOS vs clipped-sine output?: CMOS simplifies digital domains but can add switching noise; clipped-sine reduces EMI and can improve reciprocal mixing. Follow the RF front-end input recommendations.
What about Allan deviation and g-sensitivity?: Low Allan deviation reduces short-term wander in the carrier loop; low g-sensitivity helps in high-dynamic platforms (UAVs, automotive) to prevent microphonic-induced jitter.
Automotive qualification?: For automotive GNSS, consider AEC-Q200 variants and extended temperature ranges (e.g., −40~+105 °C) with documented aging and shock performance.

Product Application

TCXO for GNSS Timing Guide