Crystal oscillators primarily serve to provide precise clock signals to chips. As the "heart" of a chip, crystal oscillators play an irreplaceable role in oscillation circuits. So, what are the basic parameters of crystal oscillators? Let's take a look with Interquip, a crystal oscillator manufacturer.

Crystal oscillators can be divided into passive crystal oscillators and active crystal oscillators. First, let's look at the parameters of passive crystal oscillators (crystal resonators):

Basic parameter requirements proposed by the demand side:

Nominal frequency: Frequency
Load capacitance: CL
Equivalent impedance: Rr (ohms)
Frequency temperature characteristics: TC (Relative to 25℃)
Other requirements: Operating temperature range, C0, C1, etc.

Parameters to be controlled by the supplier:

Frequency accuracy: FL or FR (ppm)
Equivalent resistance: Rr (ohms)
Static capacitance: C0 (pF)
Dynamic capacitance: C1 (fF)
Equivalent inductance: L (mH)
Quality factor: Q(k)
Pullability: TS (ppm/pF)
Drive level dependency: DLD
Frequency temperature characteristics: TC (Relative to 25℃)

Parameters of active crystal oscillators (crystal oscillators):

Room temperature frequency deviation (Frequency Tolerance)
The deviation of the output frequency of the crystal oscillator (under reference conditions) from the standard frequency. For example, +/-25PPM...

Frequency temperature deviation (Frequency Stability)
The frequency variation of the crystal oscillator within the operating temperature range. For example, +25PPM, +/-30PPM...

Overall frequency deviation (Overall Stability)

The allowable frequency deviation within the specified operating conditions. The overall frequency deviation includes frequency deviation, frequency temperature deviation, voltage frequency variation, load variation, aging, etc.

Applications requiring frequency stability of ±20ppm or above: Crystal oscillators;
Applications requiring frequency stability of ±0.5 to ±10ppm: TCXO;
Applications requiring frequency stability of ±1ppm or below: OCXO.

Power supply and load
The frequency of crystal oscillators is affected by power supply voltage variations and load variations.

Rated voltages include: 3.3V+/-10% or 5V+/-10%, 1.8V+/-5%, 2.8V+/-5%, etc. The rated load for CMOS output is 15pF.

Output waveform
Crystal oscillators have CMOS, TTL, PECL, LVPECL, LVDS, HCSL.

Measurement instruments include frequency counters, oscilloscopes, etc.