When the parasitic frequency signal level is as strong as the main frequency, the oscillator will oscillate on the parasitic frequency. This phenomenon is called frequency hopping. Parasitic frequency patterns are often defined as resistivity or suppression ratios for frequency. For most oscillators, the frequency of resistance between 1.5 and 2.0 can prevent frequency hopping. The equivalent of -3 DB to -6db suppression ratio.

XO is a common crystal oscillator, no temperature compensation or voltage control to fine-tune the output frequency, Temperature characteristics are mainly caused by the crystal itself.

The VCXO voltage-controlled crystal oscillator is an oscillator with a foot that can be used to fine-tune the output frequency by an external voltage.

TCXO is a kind of crystal oscillator with temperature compensation circuit inside, and the output frequency has good stability when the working temperature is changing.

The Crystal resonator is applied to the computer/interface card/telephone/pager/REMOTE Control/GPS/audio/video products,

Oscillators are mainly used in computer/GPS/audio/video products,

VCXO mainly used in modem/wireless base station/SPC,

TCXO/VCTCXO mainly used in mobile phone/wireless base station/precision instrument/GPS,

Filter mainly used in mobile phone/wireless Transceiver.

The "load capacitance" on the oscillating line is defined as: all capacitance values encountered by the oscillator line are viewed from the two terminals of the quartz crystal resonator. The load capacitor can be connected with quartz crystal resonator in parallel  or in series in line.

The size of the load capacitance (CL) affects the characteristic of the nominal frequency in the oscillating line connected in parallel mode.

The resonance frequencies of this parallel line of load capacitance are expressed in FL:

Negative impedance is the value of the impedance characteristic of the oscillator line when the oscillation frequency is seen from the two terminals of the quartz crystal resonance oscillator. Sufficient amplification gain value must be provided on the oscillating circuit to compensate the mechanical energy loss of the quartz crystal resonator at resonance. Negative impedance is not the product parameter of quartz oscillator, but an important characteristic parameter of oscillatory circuit. From the point of view of the resonance, it is the "negative impedance" of the oscillating line.

 Simply put, in the design of high-frequency oscillator, the amplifier will face low high-frequency gain and high crystal equivalent resistance.