Temperature Characteristics and Type Selection of Thermal Crystal Oscillator

With the development of miniaturization and high performance of intelligent terminals, it is very necessary to have a crystal oscillator device that can generate stable clock reference signals. 

Under this background, thermal crystal oscillator is developed. The thermal crystal oscillator has the frequency stability close to the temperature compensated crystal oscillator (TCXO), with smaller size and lower price. It is the best substitute for TCXO.

Working Principle

The thermal crystal oscillator counteracts the influence of temperature change on the crystal frequency through a compensation network. With an appropriate chipset, the precise temperature compensation function of the thermosensitive crystal oscillator can work, providing very strict frequency stability.

The compensation idea is that the compensation network drives the clamping network, and the clamping network adjusts the output frequency of the crystal oscillator. During operation, the configured compensation network is used to sense the surrounding temperature of the crystal oscillator, and continuously correct the frequency, clamping the frequency parameters of the crystal oscillator to the nominal value.

In the standard oscillation circuit, the nominal frequency deviation of the crystal resonator is obtained at room temperature (+25 ° C), generally 5~10ppm. According to the different cutting directions of the quartz rough embryo, there will be a significant frequency shift within the specified working temperature range, which is the temperature stability. 

The thermosensitive crystal oscillator allows users to understand the temperature feedback, and makes the frequency stability do the crystal oscillator as stable as possible through appropriate compensation measures. 

The effect of compensation network is obvious. The goal is to generate a voltage signal to map the frequency offset caused by temperature change. 

If the correction voltage is applied, we can effectively remove the frequency shift caused by temperature change and obtain a very stable frequency temperature curve.

Technical Advantages

The thermal crystal oscillator is formed by the integration of standard crystal oscillator, thermistor (NTC) and varactor diodes. 

Compared with the traditional application of separating crystal oscillator and temperature sensor, the new method has many obvious advantages: 

(1) The temperature sensor can feed back the real-time crystal temperature.

(2) The number of components is reduced, the PCB area is saved, and the circuit design is simplified. 

(3) Compared with uncompensated crystal oscillator, it has obvious advantages of frequency stability.

In short, compared with the standard crystal resonator, the frequency stability ,temperature stability of the thermal crystal resonator is improved by more than 20 times, which can replace TCXO products in precision applications at present. 

Model selection reference

The thermal crystal oscillator has good frequency stability, and the frequency accuracy is greatly improved compared with the standard crystal oscillator. Generally, the frequency difference of standard crystal oscillator is ± 20ppm, that of thermal crystal oscillator is ± 10ppm, and that of temperature compensated crystal oscillator can reach ± 0.5ppm. Thermal crystal oscillator is widely used in high frequency and wide temperature applications, including small wireless devices, wireless modules, IOT devices, wearable devices, TWS Bluetooth headsets, health devices and small consumer products. 

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