The Differences between TCXO and VCTCXO | Xtalong

A temperature-compensated crystal oscillator is a device that converts DC power into AC power. Based on its advantages of wide operating temperature range, high frequency stability, low power consumption, small size, high reliability, and short time required to reach the specified frequency stability, it is widely used in communication products, such as network communication, remote control, etc. , positioning and navigation systems, etc.


The temperature-compensated crystal oscillator is actually a combined component. Its built-in crystal oscillator must be a high-quality crystal oscillator. In addition to the equivalent resistance being less than 30Ω, the following additional requirements are required:

1. The smoothness of the frequency-temperature characteristic curve should be less than the compensation accuracy

2. The frequency-temperature characteristic curve is consistent, and the high-temperature inflection point is concentrated below 45°C

3. Low aging rate

4. In order to increase the frequency modulation sensitivity, the quartz wafer electrode and static capacitance are also slightly larger

5. The cutting angle tolerance of the quartz wafer should be small to ensure the consistency of the curve


According to the compensation method, temperature-compensated crystal oscillators can be divided into two categories


Indirect Compensated Quartz Crystal Oscillator (Chinese abbreviation: Voltage Controlled Temperature Compensated Crystal Oscillator, English abbreviation: VCTCXO)


The nonlinear frequency drift of the quartz wafer is compensated by the variation of the series capacitance of the quartz wafer. This compensation method can achieve a high precision of ±0.5ppm, but it is limited in the case of low voltage below 3V. That is, a temperature compensation resistor network is added to the front end of the voltage-controlled crystal oscillator (VCXO), and the output voltage of the compensation network is used to control the control terminal voltage of the VCXO, that is, a voltage-controlled temperature-compensated crystal oscillator (VCTCXO: Voltage Controlled & Temperature Compensated Crystal Oscillator).


Direct Compensation Quartz Crystal Oscillator (Chinese abbreviation: Temperature Compensated Crystal Oscillator, English abbreviation: TCXO)


Directly compensated TCXO (Temperature Compensated Crystal Oscillator) is a temperature compensation circuit composed of a thermistor and a resistance-capacitance element, which is connected in series with a quartz crystal in the oscillator. When the temperature changes, the resistance value of the thermistor and the capacitance value of the equivalent series capacitance of the crystal change accordingly, thereby offsetting or reducing the temperature drift of the oscillation frequency. That is, a temperature-sensitive compensation resistance-capacitance network is directly added to the oscillation tank of the crystal oscillation circuit to achieve the purpose of compensation.  The latter saves the VCXO in the circuit, and does not need to stabilize the oscillation circuit, so it has certain advantages in terms of circuit, power consumption, and volume.