How does oscillator crystal circuit work | Xtalong
How does oscillator crystal circuit work？
Generally, the demitasse oscillator crystal circuit sustains oscillation by taking a voltage signal from the quartz resonator,
amplifying it, and feeding it back to the resonator. The rate of expansion and
compression of the quartz is the reverberative frequency, and is determined by the cut and size of the demitasse.
Electrically, oscillator crystal circuit can be equivalent to a two terminal network in
which a capacitor and a resistor are connected in parallel and then a capacitor is connected in series.
Electrotechnics, this network has two resonance points.
The lower frequency is series resonance and the higher frequency is parallel resonance.
Due to the characteristics of the crystal itself, the distance between the two frequencies is quite close.
Within this extremely narrow frequency range, the crystal oscillator is equivalent to an inductance.
Therefore, as long as appropriate capacitors are connected in parallel at both ends of the crystal oscillator,
it will form a parallel resonant circuit.
This parallel resonant circuit can be added to a negative feedback circuit to form a sine wave oscillation circuit.
Because the frequency range of crystal oscillator equivalent to inductance is very narrow,
even if the parameters of other components change greatly, the frequency of this oscillator will not change much.
The oscillator crystal circuit is connected to the crystal oscillator at both ends of an inverse amplifier,
and then two capacitors are connected to both ends of the crystal oscillator respectively,
and the other capacitor is grounded. The capacitance of these two capacitors in series is equal to the load capacitance.
An important parameter of the crystal oscillator is the load capacitance value.
By selecting a parallel capacitor equal to the load capacitance value,
the nominal resonant frequency of the crystal oscillator can be obtained.
In general, the oscillator crystal circuit is connected to the crystal oscillator at both ends of an inverse amplifier
(note that the amplifier is not an inverter), and then two capacitors are connected to both ends of the crystal oscillator respectively,
and the other end of each capacitor is connected to the ground. The capacity value of the two capacitors
in series should be equal to the load capacitance. Please note that the pins of general IC have equivalent input capacitance,
which cannot be ignored.
In a brief, oscillation circuit can produce oscillation current whose magnitude and direction change with the period.
This oscillating current circuit is called an oscillating circuit. The oscillation circuit is composed of an amplifier and a feedback network.
The amplifier circuit can supplement the energy loss. The positive feedback network can make the circuit produce sine wave signal.