Essential Selection of Crystal Oscillator: Complete Analysis of Core Professional Terms for Quartz Crystal Oscillator
To gain a deeper understanding of an industry, mastering the professional terminology of its core products is a crucial step, and the quartz crystal oscillator field is no exception. Mastering these terms can not only make the procurement and selection of crystal oscillators more efficient, but also effectively avoid circuit problems caused by parameter mismatches. Below, we will interpret the core professional terms of quartz crystal oscillators from three dimensions: frequency, capacitance, resistance, and other key indicators.
1. Frequency related terms
Frequency is the most fundamental parameter of a crystal oscillator, and understanding the following concepts is the first step in selection:
Nominal frequency: refers to the frequency value specified in the technical specifications of the crystal, usually directly marked on the outer shell of the crystal oscillator, and is the most basic frequency identification of the product.
Working frequency: This is not the frequency generated by the crystal oscillator alone, but the actual operating frequency generated by the interaction between the crystal and the supporting working circuit.
Adjust frequency difference: Under standard operating conditions, with a reference temperature of 25 ± 2 ℃, the allowable deviation range between the operating frequency of the crystal oscillator and the nominal frequency.
Temperature frequency difference: Under specified conditions, when the ambient temperature varies throughout the entire operating temperature range, the allowable deviation value of the crystal oscillator operating frequency relative to the frequency at a reference temperature of 25 ± 2 ℃.
Load resonant frequency (fL): The characteristic frequency that occurs when a crystal is connected in series or parallel with a load capacitor under specific conditions, and the overall impedance exhibits pure resistance characteristics. If it is a series load capacitor, the resonant frequency of the load is the one with the lower value; If it is a parallel load capacitor, it is the one with the higher value.
Fundamental frequency: The lowest order vibration frequency in the crystal oscillator vibration mode, which is the most fundamental vibration frequency of the crystal oscillator.
Pantone: a mechanical harmonic generated by crystal vibration, whose frequency is close to an integer multiple of the fundamental frequency, but not strictly an integer multiple (this is its core difference from electrical harmonics). Common overtone vibrations include 3, 5, 7, and so on.
2. Terminology related to capacitors and resistors
In the equivalent circuit model, the capacitance and resistance parameters directly determine the oscillation and stability of the crystal oscillator:
Static capacitance (C0): In the equivalent circuit of a crystal oscillator, the capacitance connected in parallel with the series arm, also known as the shunt capacitance, is usually represented by the symbol C0.
Load capacitance (CL): It is an external effective capacitance used in conjunction with a crystal to jointly determine the resonant frequency fL of the load. The optional series values are usually within the range of 6-33pF, and when selecting, it is recommended to prioritize standard values such as 7pF, 9pF, 12pF, 15pF, and 18pF.
Dynamic resistance (R1): Refers to the equivalent resistance of a crystal oscillator at the series resonant frequency, with R1 as the identification symbol.
Load resonant resistance (RL): It is the equivalent resistance exhibited by a crystal oscillator at the load resonant frequency, expressed as RL=R1 (1+C0/CL) ², where R1 is the dynamic resistance, C0 is the static capacitance, and CL is the load capacitance.
3. Other key terms
In addition to frequency and impedance, the following parameters determine the long-term reliability and operating state of the crystal oscillator:
Aging rate: Under the specified working environment and conditions, the operating frequency of the crystal oscillator will slowly change over time, and the relative allowable range of this change is the aging rate. If measured in years, it is called the annual aging rate.
Excitation level: a parameter used to characterize the power consumption of a crystal oscillator during operation. Common optional values include 100 μW, 50 μW, 20 μW, 10 μW, 1 μW, 0.1 μW, etc. Different excitation levels will directly affect the performance and stability of the crystal oscillator.
