RFTCXO vs VC-TCXO: Detailed Comparison of Crystal Oscillators
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.
