working of piezoelectric oscillator| Xtalong
Piezoelectric oscillator are also known as quartz crystals, quartz resonators or passive crystal oscillators. The working principle of the piezoeletric oscillator is a passive resonant element made of the piezoelectric effect of the quartz crystal. It can be used together with semiconductor devices, resistors and capacitors to form a complete set of quartz crystal oscillator circuits.
Piezoelectric effect of quartz crystal: Applying a mechanical force to the quartz crystal causes the relative displacement of their internal positive and negative charge centers, resulting in polarization, which leads to the appearance of bound charges of opposite signs on the surfaces of the two ends of the quartz crystal. Within a certain stress range, the relationship between mechanical force and electric charge is linear and reversible. This phenomenon is called the piezoelectric effect of quartz crystals.
The role of quartz crystal resonators: to provide oscillation pulses, stable frequencies and frequency selection for digital systems.
Classification of quartz crystal resonators: plug-in type and SMD type. The plug-in type is suitable for manual welding, and the patch type is suitable for automatic SMT placement.
Main parameters of quartz crystal resonators:
1. Nominal frequency: Under specified conditions, the resonance center frequency of the quartz crystal resonator.
2. Frequency tolerance: Under the specified conditions, the maximum deviation value of the operating frequency at the reference temperature relative to the nominal frequency PPM (Parts Per Million).
3. Frequency stability: Under specified conditions, within the entire working temperature range, the allowable deviation of the working frequency relative to the reference temperature.
4. Load resonance resistance: The resistance value when the quartz crystal resonator is connected in series with the specified external capacitor and oscillates at the load resonance frequency.
5. Load capacitance: refers to the effective capacitance that determines the load resonance frequency together with the quartz crystal resonator. Commonly used load capacitances are: 8pF, 9pF, 12pF, 12.5pF, 15pF, 16pF, 18pF, 20pF, etc.
6. External capacitor: refers to the capacitive element in the circuit in which the frequency output pin of the quartz crystal resonator is connected in series with the input pin. Its function is to fine-tune the accuracy of the actual output frequency of the crystal oscillator through adjustment.