How to choose temperature compensated crystal oscillator correctly

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Precision, low power consumption and miniaturization are still the unchanging research topics of temperature-compensated crystal oscillators. In terms of miniaturization and chip-type, there are many difficulties, of which there are two main points: First, miniaturization will reduce the frequency variable amplitude of the quartz crystal oscillator, making temperature compensation more difficult; second, after chip packaging, during the connection operation, the welding temperature is much higher than the maximum allowable temperature of the temperature-compensated crystal oscillator, which will cause the frequency of the crystal oscillator to change. If local heat dissipation and cooling measures are not taken, it is difficult to control the frequency change of the temperature-compensated crystal oscillator to less than ±0.5×10-6. However, the improvement of the technical level of temperature-compensated crystal oscillators has not reached its limit, and the content and potential of innovation are still large. Below Easy-Key will briefly introduce the parameter requirements of temperature-compensated crystal oscillators!

1. Frequency accuracy. When the standard power supply voltage, standard load capacitance impedance, reference temperature (25°C) and other conditions remain unchanged, the maximum allowable deviation of the frequency of the quartz crystal oscillator relative to its specified nominal value shall not exceed ±50. 2. Temperature stability. When other specifications remain unchanged, the maximum change in the output frequency of the quartz crystal oscillator within the specified temperature range is the allowable frequency deviation value relative to the sum of the output frequency extremes within the temperature range, that is, (fmax-fmin)/(fmax+fmin). Frequency adjustment range: The range of output frequency changed by adjusting a variable element of the crystal oscillator. FM (voltage control) characteristics: including FM deviation, FM sensitivity, and FM linearity. ① FM deviation: the output frequency difference when the control voltage of the voltage-controlled oscillator changes from the nominal maximum value to the minimum value. ② FM sensitivity: the change in output frequency caused by a unit change in the external control voltage of the voltage-controlled crystal oscillator. ③ FM linearity: a measure of the transmission characteristics of a modulation system compared with an ideal straight line (least square method). 66)]

Load characteristics: When other conditions remain unchanged and the load is within the specified range, the maximum allowable frequency deviation of the crystal oscillator output frequency relative to the output frequency under the nominal load.

Voltage characteristics: When other conditions remain unchanged and the power supply voltage is within the specified range, the maximum allowable frequency deviation of the crystal oscillator output frequency relative to the output frequency under the nominal power supply voltage.

Clutter: The power ratio of the discrete spectrum components in the output signal that have no harmonic relationship with the main frequency (except subharmonics) to the main frequency, expressed in dBc. Harmonic: The ratio of the harmonic component power Pi to the carrier power P0, expressed in dBc. Frequency aging: The systematic drift of the output frequency over time caused by the aging of components (mainly quartz resonators) under specified environmental conditions. It is usually measured by the frequency difference within a certain time interval. For high-stability crystal oscillators, since the output frequency drifts in a single direction approximately linearly over a long working time, the aging rate (relative frequency change per unit time) is often used to measure it.