Quartz crystal resonators are mainly used for frequency control and frequency selection circuits. This guide helps to ensure that performance is not satisfactory, cost is not appropriate and availability is not good.

Vibration mode and frequency

Base frequency 1 ~ 35MHz

3 times overtone 10 ~ 75MHz

5 times overtone 50 ~ 150MHz

7 times over tone 100 ~ 200MHz

9 overtones 150 ~ 250MHz

Crystal resistance

For the same frequency, when working in high-order overtone vibration, the resistance value will be greater than when working in low-order vibration.

Temperature difference

When setting the temperature difference, consider the temperature rise tolerance caused by the equipment work. When the temperature difference requirements are high, while space and power are allowed to take the case, should be considered constant temperature work, thermostat crystal oscillator is designed for this purpose.

Load capacitance and frequency traction

In many applications, it is necessary to use a load reactance element to traverse the crystal frequency, which is necessary in phase-locked loop and frequency modulation applications. In most cases, this load reactance is capacitive. When the capacitance is CL , The relative load resonance frequency offset is: DL = C1 / [2 (C0 + CL)]. And CL as an adjustable element from DL1 to DL2, the relative frequency of traction:

DL1, L2 = C1 (CL1-CL2) / [2 (C0 + CL1) (C0 + CL2)].

The choice of load capacitance

Crystal work at the fundamental frequency, the load capacitance of the standard values of 20PF, 30PF, 50PF, 100PF. The overvoltage crystal often operates in series resonances. Where load capacitance is used, the load capacitance value should be selected from the following standard values: 8PF, 12PF, 15PF, 20PF, 30PF.

The effect of the excitation level

In general, the AT cut crystal excitation level increases, the frequency change is positive. Excessive excitation levels can cause non-linear effects, leading to possible parasitic oscillations; severe thermal drift; over-stress drift and resistance mutations. When the excitation level is too low will cause the starting resistance is not easy to overcome, poor work and indicators of instability.

Application of Filtering Circuit

In the filter circuit, in addition to the usual provisions, but should pay attention to its equivalent circuit components of the numerical and error and parasitic response to the location and amplitude, due to the special nature of the filter crystal design, so the user should be specified when the purchase.