VCXO Family for Communication Sync, PLL & Timing CPE

Q: Where does a VCXO sit in a communication synchronization PLL?

A VCXO is commonly used as the controllable reference element inside a PLL or clock-cleaner loop. The loop adjusts the VCXO frequency via the tuning (control) voltage to lock to a reference while shaping phase noise across the loop bandwidth.

Q: How do I choose the required pull range (APR) for my PLL?

Select a pull range that covers initial frequency tolerance, aging, and temperature drift plus any expected reference offsets. Keep adequate margin so the PLL operates within the linear tuning region without saturating the control voltage.

Q: What jitter specification matters most for VCXO selection?

For many systems, integrated phase jitter over the integration band relevant to your link or ADC/DAC clocking is the most actionable metric. Also check phase noise offsets around your PLL bandwidth because the loop will trade reference noise vs VCXO noise.

Q: CMOS vs clipped-sine VCXO—how do I decide?

CMOS is common for general digital clock distribution and easy interfacing. Clipped-sine can be preferred in some analog clocking or when the receiver expects a sine-like input. Choose based on downstream receiver requirements and EMI/jitter trade-offs.

Q: What board-level items most often break VCXO performance?

Power and VCTRL noise coupling, poor grounding, excessive coupling from aggressor clocks, and incorrect termination/loading can all degrade jitter and tuning behavior. Keep the control node clean, use proper decoupling, and verify loop stability on the bench.

Q: Which FCom VCXO should I choose for a 5.0×3.2mm CMOS timing design?

For mainstream timing CPE and communication synchronization loops, start with FVC-5X (CMOS VCXO). If your jitter budget is tighter (clock cleaner / SyncE / IEEE 1588), consider the low-jitter FASTVCXO option FVC-5P-LJ.

Q: Do I need a differential VCXO (LVDS/LVPECL) and which models are available?

Differential VCXO is recommended for impedance-controlled clock pairs (SerDes, optics, ADC/DAC clocking) and improved high-speed margins. Representative models include FVC-3L-PG (3.2×2.5mm), FVC-5L-PG (5.0×3.2mm) and FVC-7L-PG (7.0×5.0mm).

A VCXO (Voltage Controlled Crystal Oscillator) is the frequency-tunable element in many PLL-based synchronization systems. For SyncE / IEEE 1588 clocks, timing CPE, broadcast timing trees, and clock cleaners, VCXO selection is driven by pull range, phase noise / jitter, tuning linearity, and practical footprint options.

PLL Reference SyncE / IEEE 1588 Timing CPE Low Jitter Options SMD 3.2×2.5 / 5.0×3.2 / 7.0×5.0

FCom Fuji Crystal VCXO family for communication synchronization and PLL timing: low jitter, stable pull range and SMD packages for SyncE, IEEE 1588 and timing CPE.

Where VCXO Fits in a Sync & Timing System

Typical PLL / Clock Cleaner Loop

In a PLL, the VCXO provides a crystal-based oscillator whose frequency can be trimmed via VCTRL. The loop filter shapes how reference noise and VCXO noise contribute to output jitter.

Why VCXO (not XO) in Sync Loops

A fixed XO cannot correct frequency offsets once assembled. A VCXO enables continuous frequency control for lock acquisition, drift correction and holdover strategies in timing-aware systems.

Typical VCXO Family Parameters

Core Specs

Frequency (e.g., 25 / 125 / 156.25 / 622.08 MHz)
Pull range (APR) (e.g., ±50 / ±100 / ±150 ppm)
Control voltage range (typ. 0.3–2.7V or per loop)
Output (CMOS, clipped sine; differential in special cases)

Noise / Stability Specs

Phase noise at offsets around PLL bandwidth
Integrated RMS jitter over required band
Stability / aging per system holdover margin
Temperature range per deployment (indoor / outdoor / telecom)

Variant Quick View (Packages & Integration Notes)

VCXO – SMD 3.2×2.5 mm (CMOS)

Best for	Dense clock trees, compact modules, and cost-sensitive designs
Typical pull range	±10 ppm to ±200 ppm (project dependent)
Integration focus	Power/VCTRL noise isolation, tight decoupling, and loop stability margin in small layouts
Recommended FCom parts	FVC-3X CMOS VCXO (3.2×2.5mm) · FVC-3P-LJ Low Jitter VCXO (3.2×2.5mm) · FVC-3L-PG Differential VCXO (LVDS/LVPECL)

VCXO – SMD 5.0×3.2 mm (CMOS)

Best for	Mainstream SyncE / IEEE 1588 timing designs and clock distribution
Typical pull range	±50 ppm / ±100 ppm / ±150 ppm
Integration focus	Loop bandwidth vs reference noise trade-offs; linear tuning region selection
Recommended FCom parts	FVC-5X CMOS VCXO (5.0×3.2mm) · FVC-5P-LJ Low Jitter FASTVCXO (5.0×3.2mm) · FVC-5L-PG Differential VCXO (LVDS/LVPECL)

VCXO – SMD 7.0×5.0 mm (CMOS)

Best for	Boards needing robust assembly and relaxed area constraints
Typical pull range	±50 ppm / ±100 ppm / ±150 ppm
Integration focus	EMI management and clean VCTRL routing in larger clock trees
Recommended FCom parts	FVC-7X CMOS VCXO (7.0×5.0mm) · FVC-7P-LJ Low Jitter FASTVCXO (7.0×5.0mm) · FVC-7L-PG Differential VCXO (LVDS/LVPECL)

Recommended FCom VCXO Products

Below is a practical VCXO selector aligned to common communication synchronization, PLL reference, and timing CPE scenarios. It links directly to representative FCom Fuji Crystal VCXO models.

Application map CMOS VCXO Low-jitter CMOS Differential (LVDS/LVPECL)

Application → VCXO selection map

Use-case	Clock examples	Output	Recommended VCXO	Selection note
SyncE / IEEE 1588 timing cards, clock cleaners	122.88 / 125 / 155.52 / 156.25 MHz	CMOS or Differential	FVC-5P-LJ · FVC-5L-PG	Prioritize low RMS jitter and stable pull range (APR) for predictable loop behavior.
Timing CPE: gateways / cable modems / xDSL / VoIP	25 / 27 / 54 / 74.25 / 148.5 MHz	CMOS	FVC-5X	Mainstream 5.0×3.2mm VCXO for cost-optimized timing trees.
Optical modules (SFP/QSFP), dense networking modules	125 / 156.25 / 200 / 491.52 MHz	Differential	FVC-3L-PG	3.2×2.5mm differential outputs for tight routing and high-speed margins.
High-speed ADC/DAC sampling clocks (fine trim)	10–1500 MHz (device dependent)	Differential	FVC-5L-PG · FVC-7L-PG	Wide frequency coverage with impedance-controlled pairs; commonly used as clock-cleaner references.
General-purpose VCXO (relaxed jitter budget)	2–66 MHz / up to 250 MHz	CMOS	FVC-3X · FVC-7X	Broad compatibility and footprint flexibility for legacy clock trees.

CMOS VCXO

FVC-5X — 5.0×3.2mm CMOS VCXO

1.5–170 MHz; APR ±50 ppm; 1 ps jitter (12 kHz–20 MHz, typical)
3.3 V; mainstream timing CPE and communication sync applications

FVC-3X — 3.2×2.5mm CMOS VCXO

2–66 MHz; minimum APR ±150 ppm; 1.2 ps jitter (typ.)
2.8 V / 3.3 V; compact boards and legacy clock trees

FVC-7X — 7.0×5.0mm CMOS VCXO

7×5mm footprint; tri-state CMOS; frequency options up to 250 MHz
Robust assembly for routers, timing cards, and general comm equipment

Low-jitter CMOS (FASTVCXO)

FVC-5P-LJ — Low Jitter FASTVCXO (5.0×3.2mm)

10–250 MHz; <0.8 ps RMS jitter (12 kHz–20 MHz); typical APR ±50 ppm
2.5 V / 3.3 V; SyncE / IEEE 1588 and clock cleaner references

FVC-3P-LJ — Low Jitter VCXO (3.2×2.5mm)

10–250 MHz; 0.6 ps typ. (integer mode); APR ±50 / ±150 ppm options
2.5 V / 3.3 V; dense modules and compact networking designs

FVC-7P-LJ — Low Jitter FASTVCXO (7.0×5.0mm)

10–250 MHz; <1 ps typ. (12 kHz–20 MHz); APR ±50 ppm
3.3 V; low jitter reference in 7×5mm footprint

Differential VCXO (LVDS / LVPECL)

Choose differential output when your clock tree is impedance-controlled and sensitive to common-mode noise or EMI, or when you need stronger high-speed margins for SerDes, SyncE, or ADC/DAC clocking.

FVC-3L-PG — 3.2×2.5mm Differential VCXO

LVDS / LVPECL; 10–1500 MHz; ~0.6–0.8 ps RMS jitter; APR ±50 / ±150 ppm options
Compact differential reference for optics and dense networking modules

FVC-5L-PG — 5.0×3.2mm Differential VCXO

LVDS / LVPECL; 10–1500 MHz; <1 ps RMS jitter; APR ±50 ppm
Balanced choice for compact boards needing differential clock pairs

FVC-7L-PG — 7.0×5.0mm Differential VCXO

LVDS / LVPECL; 10–1500 MHz; <1 ps RMS jitter; APR ±50 ppm
Telecom synchronization, clock cleaners, and high-speed ADC/DAC clocks

For fast quoting and the correct pulling range, please share: target F_o, output format, supply, APR, temperature range, and jitter integration band.

Explore: Timing Devices · VCXOs

Lab Validation Checklist (Avoid Hidden Jitter)

Power & Control Node

Measure VDD ripple and correlate with phase noise
Filter VCTRL (loop filter output) against switching noise
Keep VCTRL routing short and away from aggressors

PLL Loop & Output Interface

Validate loop stability across temperature and supply corners
Confirm output loading/termination per receiver spec
Verify jitter integration band matches system requirements

FAQ

Where does a VCXO sit in a communication synchronization PLL?

A VCXO is commonly used as the controllable reference element inside a PLL or clock-cleaner loop. The loop adjusts the VCXO frequency via the tuning (control) voltage to lock to a reference while shaping phase noise across the loop bandwidth.

How do I choose the required pull range (APR) for my PLL?

Select a pull range that covers initial frequency tolerance, aging, and temperature drift plus any expected reference offsets. Keep adequate margin so the PLL operates within the linear tuning region without saturating the control voltage.

What jitter specification matters most for VCXO selection?

For many systems, integrated phase jitter over the integration band relevant to your link or ADC/DAC clocking is the most actionable metric. Also check phase noise offsets around your PLL bandwidth because the loop will trade reference noise vs VCXO noise.

CMOS vs clipped-sine VCXO—how do I decide?

CMOS is common for general digital clock distribution and easy interfacing. Clipped-sine can be preferred in some analog clocking or when the receiver expects a sine-like input. Choose based on downstream receiver requirements and EMI/jitter trade-offs.

What board-level items most often break VCXO performance?

Power and VCTRL noise coupling, poor grounding, excessive coupling from aggressor clocks, and incorrect termination/loading can all degrade jitter and tuning behavior. Keep the control node clean, use proper decoupling, and verify loop stability on the bench.

Which FCom VCXO should I choose for a 5.0×3.2mm CMOS timing design?

For mainstream timing CPE and communication synchronization loops, start with FVC-5X (CMOS VCXO). If your jitter budget is tighter (clock cleaner / SyncE / IEEE 1588), consider the low-jitter FASTVCXO option FVC-5P-LJ.

Do I need a differential VCXO (LVDS/LVPECL) and which models are available?

Differential VCXO is recommended for impedance-controlled clock pairs (SerDes, optics, ADC/DAC clocking) and improved high-speed margins. Representative models include FVC-3L-PG (3.2×2.5mm), FVC-5L-PG (5.0×3.2mm) and FVC-7L-PG (7.0×5.0mm).

Need a VCXO recommendation? Share your frequency, output format, supply, pull range, temperature range, and jitter integration band. Our team will suggest the best-fit VCXO family and provide footprint + documentation for PCB review.

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