Terminology » RF Components » TCXO vs VC-TCXO: Detailed Comparison of Crystal Oscillators

TCXO vs VC-TCXO: Detailed Comparison of Crystal Oscillators

crystal oscillator temperature compensation frequency stability vctcxo tcxo

Both Temperature Compensated Crystal Oscillators (TCXOs) and Voltage-Controlled Temperature Compensated Crystal Oscillators (VC-TCXOs) are designed to combat frequency variations caused by temperature changes. They employ temperature compensation techniques to maintain a stable output frequency across a defined temperature range. This makes them a preferred choice over other crystal oscillator types.

TCXOs and VC-TCXOs find use in a variety of applications, including:

Base Stations
GPS/GNSS Receivers
Industrial Instrumentation
Wireless Systems
Test and Measurement Instruments

TCXO

A TCXO is designed to operate reliably even with significant ambient temperature fluctuations. It incorporates a built-in thermistor that continuously monitors the surrounding temperature and adjusts the oscillator’s behavior accordingly.

For example, the ASTX-H11 manufactured by Abracon is a typical TCXO. Here are some of its specifications:

Frequency Stability: +/- 2.5 ppm (Parts Per Million)
Operating Temperature: -30°C to +75°C
Supply Voltage: 3.3 V
Frequency Range: 2.5 MHz to 55 MHz
Aging: +/- 1 ppm per year
Output: HCMOS
For more information, visit abracon.com.

Common features to look for in a TCXO include:

Ultra-low phase noise
Compact size
Excellent temperature stability
Low power consumption
RoHS compliance

These are important considerations when selecting a TCXO from a manufacturer.

VC-TCXO

VC-TCXO modules utilize analog techniques to correct frequency deviations.

However, VC-TCXOs do have some drawbacks:

Higher price
Larger footprint
Requirement for external components in the circuit

An example of a VC-TCXO is the SiT5356 manufactured by SiTime. Its specifications include:

Frequency Stability: +/- 0.1 ppm (initial), +/- 2.5 ppm (over temperature)
Stability across temperature: +/- 100 ppb
Supply Voltage: 2.5 V, 2.8 V, 3.0 V, 3.3 V
Frequency Range: 1 MHz to 60 MHz in 1 Hz steps
Control Voltage Range: 10% of Vdd to 90% of Vdd
Output Type: LVCMOS or clipped sinewave output
For more information, visit sitime.com.

Typical features of a VC-TCXO include:

Integrated low-noise frequency synthesizer
Wide pull range for voltage control
Excellent temperature stability
Low power consumption
Programmable features for customization
High shock and vibration resistance

Difference between TCXO and VCTCXO

The following table provides a direct comparison of TCXO and VC-TCXO characteristics:

Parameter	TCXO	VC-TCXO
Full Form	Temperature Compensated Crystal Oscillator	Voltage-Controlled Temperature Compensated Crystal Oscillator
Temperature stability	Typically stable over a temperature range, but not adjustable	Adjustability for temperature compensation
Voltage control	Not supported	Supported
Frequency adjustment	Not supported, typically fixed frequency	Frequency adjustment possible by varying voltage
Complexity	Simple design	More complex due to addition of voltage control circuitry
Power consumption	Typically lower power consumption	May have higher power consumption due to additional voltage control circuits
Size and form factor	Often compact, available in smaller packages	May be slightly larger
Frequency pulling and pushing	Less susceptible to voltage induced frequency changes	Susceptible to frequency changes with variations in control voltage, can be managed using careful design
Cost	Often lower cost compared to VC-TCXO	Typically higher cost due to additional features
Applications	Commonly used where temperature stability is desired	Suitable where fine tuning of frequency is required

In conclusion, the decision between TCXO and VC-TCXO hinges on the specific needs of the application, taking into account the necessity for frequency adjustment, temperature stability requirements, and budgetary constraints.