1. Introduction of quartz crystal resonator
Quartz crystal resonator is an important electronic component for stabilizing frequency and ing frequency. It has been widely used in various military and civilian products, such as wired communication, wireless communication, radio and television, satellite communication, navigation, electronic measuring instruments, microcomputer processing, digital intelligent instruments, clocks and watches, automobiles and so on. Our quartz crystal resonator is not only widely used in national key military and aerospace projects, but also successfully matched for Shenzhou series spacecraft and its carrier rocket.
2. Commonly used terms in quartz crystal resonators
1) Nominal Frequency: Frequency specified in the technical specifications of crystal elements, usually marked on the product shell, it has a certain difference with the actual operating frequency of crystal elements.
2) operating frequency: the oscillation frequency produced by the crystal element and its circuit.
3) Adjusted frequency difference: The maximum allowable deviation between the operating frequency and the nominal frequency at the reference temperature (25 +2) under the specified conditions.
4) Temperature Frequency Difference: The maximum allowable deviation of the operating frequency from the reference temperature (25 +2) within the specified operating temperature range.
5) Total Frequency Difference: The maximum allowable deviation from the nominal frequency in the operating temperature range under specified conditions.
6) equivalent resistance (ESR)One，RrOne，ROneAlso known as resonant resistance. Under the specified conditions, the quartz crystal resonator does not connect the resistance of the load capacitor at resonance frequency.
7) load resonant resistance (R)LThe resistance of a quartz crystal resonator and a load capacitor in series at a resonant frequency under specified conditions.
8) static capacitance (C)ZeroThe capacitor connected to the series arm in the equivalent circuit is also called capacitance.
9) load capacitance (C)lAll the effective capacitance from the two ends of the quartz crystal resonator pin to the direction of the oscillation circuit is the load capacitance added to the quartz crystal resonator by the oscillator.
10) frequency traction sensitivity (T)sFor the relative frequency traction range of the load capacitance change rate, that is, the load capacitance change 1 pF when the frequency of the relative change value, it reflects the change of load capacitance caused by frequency sensitivity, also known as frequency adjustability.
11) excitation level: effective power consumed for quartz crystal resonator.
12) fundamental frequency: the lowest vibration frequency in the mode of vibration.
13) overtone: the mechanical vibration of crystal vibrations. The ratio of overtone frequency to fundamental frequency is close to integer but not integer, which is the main difference between overtone frequency and electrical harmonics. The overtone has 3 overtones, 5 overtones, 7 overtones, 9 overtones, etc.
3. Guide for the application of quartz crystal resonators
1) Choice of load capacitor: load capacitor and quartz resonator together determine the operating frequency of the oscillator. By adjusting the load capacitor, the operating frequency of the oscillator can generally be adjusted to the nominal value. The load capacitance stipulated in the product specification is not only a test condition, but also a use condition. This value can be adjusted according to specific conditions. When the load capacitance is too large, the influence of stray capacitance decreases, but the adjustable range decreases. Increase or even shake up. The load capacitance is Series, that is series resonance.
When the crystal operates at fundamental frequency, the standard value of its load capacitance is 15pF, 20pF, 30pF, 50pF and 100pF. Overtone crystal often works in series resonance, where the load capacitor is used, its load capacitance value should be ed from the following standard values: 8pF, 12pF, 15pF, 20pF, 30pF. The calculation method of load capacitance is as follows:
2) the typical application circuit of fundamental frequency and overtone in different modes of vibration is:
The circuit of overtone crystal oscillator is slightly different from the fundamental frequency. It has an additional frequency ion circuit to filter out the fundamental frequency. When applied to CMOS oscillator circuit, in order to keep the excitation level in a certain range of numerical value and obtain stable oscillation, the Rd in the circuit diagram is essential.
3) The influence of excitation level: Generally speaking, the frequency change is positive when the excitation level of AT-cut crystal increases. The excitation level specified in each product specification is a test condition and a use condition. The excitation level can be adjusted appropriately in actual use. High excitation level will cause nonlinear effects, which may lead to parasitic oscillation, severe thermal drift, over-stress drift and sudden change of resistance. When the excitation level is too low, the vibration resistance is difficult to overcome, the work is not good and the index is unstable. Commonly used standards are 50uW, 100uW, 300uW, 500uW and 1000 uW.