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32.768KHz Tuning fork crystal oscillator

  • 2019-08-06 08:31:50

32.768KHz Tuning fork crystal oscillator

A-Crystal SMD 32.768KHz

SMD 32.768KHz

Tuning fork electrode diagram

Frequency calculation of tuning fork resonator

It shows that the frequency and resonant resistance of tuning fork crystal resonator will be very different in vacuum state and atmospheric state.

(1) . In vacuum state, the frequency will increase about 7-15hz (the increase depends on the size of tuning fork piece).

(2) In vacuum, the resonant resistance decreases by 7-10 times (the size of the tuning fork is related to the frequency of the tuning fork resonator). The formula for calculating the frequency of the tuning fork resonator is as follows:

tuning fork resonator

Circuit design

1. Compared with hc-49u, the tuning fork type quartz crystal resonators (such as dt-206 dt-308, pmx-206) are of low excitation power. Before use, the crystal current must be checked in a practical installation circuit.

2. The negative impedance of the circuit should be checked. The negative impedance (-R) should be more than 5 times the resonant impedance Re.

3. When the c-mos oscillator is used , the Rd in the circuit diagram is necessary. If Rd meets the requirement, the excitation power will remain within the specified value, and the resonant frequency will be stabilized.

4. In 10-30pf, c1 and c2can be used. If C1 and c2 < 10pf or > 30pf, the oscillation will be easily affected by the circuit phenomenon, the excitation power will increase, or the negative impedance will decrease, which will eventually lead to the instability of the oscillation.

5. The design of crystal oscillation circuit should be as brief as possible.

6. Stray capacitance between circuit and circuit board should be minimized.

7. Try to avoid crystal oscillation through other circuits.

8. If the circuit is in ic mode and the ic is manufactured differently, the frequency, excitation power, and negative impedance must be confirmed.

Basic Parameter

1. Nominal frequency: the nominal value of the central frequency or frequency of the oscillator's output.

2. Frequency accuracy: deviation of oscillator output frequency relative to nominal frequency at 25 ℃ ±2 in room temperature shift room .

3. Adjust frequency difference: the maximum allowable frequency deviation of the oscillator's output frequency relative to the measured value at 25 in a specified temperature range.

4. Static capacitance: in equivalent circuits, a capacitor connected to a series arm, also known as a parallel capacitance, usually expressed in c 0.

5. Load capacitance: an effective external capacitance, expressed in cl, that determines the resonant frequency of a load together with a crystal.

6. Operating temperature range: can ensure the oscillator output frequency and its various characteristics in accordance with the target temperature range.

7. Excitation level: the characteristic value of the power consumed in the operation of the crystal. The excitation level is less than 1 μ w.

8. Aging rate: the relative change of the output frequency within a specified time.

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