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Principle of crystal oscillator circuit

Release date:2020-04-01

Crystal oscillator is short for crystal oscillator. In electrical terms, it is equivalent to a network of capacitors and resistors in parallel to a series capacitor. From the point of view of electricity, the network has two common vibration points. Because of the properties of the crystal itself, the distance between the two frequencies is very close. In this extremely narrow frequency range, the crystal vibration is equivalent to the inductance, so as long as the appropriate capacitance is connected to both ends of the crystal vibration, a parallel resonance circuit will be formed. The parallel resonant circuit can be added to the negative feedback circuit to form a sinusoidal oscillator circuit. Since the frequency range of the crystal oscillator equivalent to the inductance is very narrow, the frequency of the oscillator will not change much even if the parameters of other components vary greatly. The crystal oscillator has an important parameter, that is, the value of the load capacitance. General vibration crystal oscillation circuit are in an inverting amplifier (note that the amplifier is not inverter) on both ends of the crystal, the other two capacitance respectively at both ends of the crystal, each capacitor located at the other end of the receiving, its capacitance is two series capacitor value should be equal to the load capacitance, please pay attention to the general IC pin has the equivalent input capacitance, this should not be ignored. In general, the load capacitance of crystal vibration is 15p or 12.5p. If the equivalent input capacitance of the element pin is considered, an oscillating circuit with two 22p capacitors forming crystal vibrations is a better choice.