Several Main Parameters of Temperature Compensated Crystal Oscillator

There are many parameters for temperature-compensated crystal oscillators. In the actual application of temperature-compensated crystal oscillators, in addition to the main parameters such as nominal frequency, PPM accuracy, and temperature stability, some other important parameters need to be paid attention to. When the standard power supply voltage, standard load capacitance impedance, reference temperature, and other conditions remain unchanged, the frequency accuracy of the temperature compensated crystal oscillator can reach more than 0.5PPM.

Fig.1

Keeping other specifications unchanged, the maximum change in the quartz crystal oscillator's output frequency within the specified temperature range is relative to the allowable frequency deviation of the sum of the output frequency extremes within the temperature range, that is, (Fmax-Fmin)/(Fmax Fmin).

By adjusting the variable element of the crystal oscillator to change the range of the output frequency, the frequency modulation (voltage control) characteristics include frequency offset, frequency sensitivity, and frequency linearity. The difference in output frequency when the voltage of a voltage-controlled oscillator changes from its nominal maximum value to its minimum value; the change in output frequency of a voltage-controlled crystal oscillator is caused by the applied control voltage per unit.

1. Frequency accuracy
When the standard power supply voltage, standard load capacitance impedance, reference temperature (25℃), and other conditions remain unchanged, the maximum allowable deviation between the frequency of the quartz crystal oscillator and its specified nominal value should not exceed ±50PPM.

2. Daily fluctuations
Within 24 hours after the specified warm-up time, the oscillator is measured every hour, and the daily fluctuation is obtained by calculating the test data according to the formula S=(fmax-fmin)/f0. Power-on characteristics, the maximum change in the oscillator frequency value within the specified preheating time is represented by V=(fmax-fmin)/f0.

3. Temperature stability
Other specifications and conditions remain unchanged. The maximum change in the output frequency of a quartz crystal oscillator within a specified temperature range is the allowable frequency offset relative to the sum of the extreme values of the output frequencies within the temperature range, that is, (fmax-fmin)/(fmax fmin).

4. Load characteristics
Other conditions remaining unchanged, the maximum allowable frequency deviation of the crystal oscillator output frequency relative to the output frequency under the nominal load is within the specified range. The maximum allowable frequency deviation of the crystal oscillator output frequency relative to the output frequency at the nominal power supply voltage is within the specified range.

5. Phase noise
The frequency domain measure of short-term stability is expressed by the ratio of single sideband noise to carrier noise\u(f), which is directly related to the spectral density S(f) of noise fluctuations and Sy(f) of frequency fluctuations, expressed by the following formula :F2s (f)=F02SY (f)=2F2. F0—carrier frequency. The power ratio of the discrete spectrum components related to the main frequency that does not contain harmonics (except sub-harmonics) in the output signal signal to the main frequency is expressed in dBc.

6. Harmonics
The ratio of component power Pi to carrier power P0 is expressed in dBc. Under specified environmental conditions, the drift process of the system output frequency over time caused by the aging of components (mainly quartz resonators) is parameter data, which is relatively important data.