As the heart of electronic equipment, crystal oscillators are the most commonly used frequency oscillators and clock devices on the market. Among various electronic devices, crystal oscillators are widely used from the simplest toys, home appliances, watches and clocks to complex computers, mobile phones, satellite navigation, cutting-edge communications, and aviation equipment. At present, high-precision temperature-compensated crystal oscillators (TCXO) The market is developing most rapidly. For example, GPS mobile phones with high-precision temperature-compensated crystal oscillators have an annual growth rate of more than 30%, and there are also fast-growing markets such as 3G mobile phones, GPS cameras and automotive electronics.
The International Electrotechnical Commission (IEC) classifies quartz crystal oscillators into four categories: ordinary crystal oscillation (SPXO), voltage controlled crystal oscillator (VCXO), temperature compensated crystal oscillation (TCXO), and thermostatically controlled crystal oscillation ( OCXO). The specific application range and corresponding frequency stability requirements can be seen in Table 1.
The frequency range is from 1 to 60 MHz. The frequency stability of TCXO with common integrated circuits can reach ±0.5～±2.5ppm. The main applications are: mobile phone, GPS navigation and positioning, two-way wireless communication equipment, etc. If the frequency stability is required to be above 0.5ppm, intelligent The TCXO temperature-compensated crystal oscillator of the clock control chip selects the digital intelligent integrated circuit for frequency twist compensation, which is usually used for the clock reference of telecommunication transmission equipment.
Constant Temperature Controlled Crystal Oscillator (OCXO) is a crystal oscillator that uses a constant temperature bath to keep the temperature of the crystal oscillator or quartz crystal oscillator constant and minimizes the variation in the oscillator output frequency caused by changes in ambient temperature. In the OCXO, some of the quartz crystal oscillators are placed in a constant temperature bath, and some quartz crystal oscillators and related important components are placed in a constant temperature bath, and some quartz crystal oscillators are placed in an internal thermostat, and The oscillating circuit is placed in an external thermostat for temperature compensation, and a double thermostatic bath control method is implemented. The proportional control of the thermostat can increase the temperature stability of the crystal by more than 5000 times, keeping the oscillator frequency stability at least 1x10-9 (on the order of ppb).
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