Chip quartz crystal resonator Apply mechanical force on some dielectrics to cause their internal positive and negative charge centers relative displacement , generated polarization Thus, binding charges with opposite signs appear on the surfaces of both ends of the medium. Within a certain stress range, the mechanical force and charge are linearly reversible. This phenomenon is called piezoelectric effect Function: provide System oscillation Pulse, stabilize frequency, select frequency a. Nominal frequency: under specified conditions resonance center frequency . b. Adjustment of frequency difference: under specified conditions, the maximum deviation of the operating frequency at the reference temperature from the nominal frequency (ppm)
c. Temperature frequency difference: the allowable deviation value of the operating frequency relative to the reference temperature within the whole operating temperature range under specified conditions
d. Load Resonance resistance : The crystal oscillator is connected in series with the specified external capacitor resonant frequency Resistance value at e. Load capacitance : refers to the effective external capacitance that together with the crystal oscillator determines the resonant frequency of the load. Common standard values are: 12pF, 16pF, 20pF, 30pF First of all Quartz crystal resonator 。 Resonators are generally divided into plug-in (Dip) and patch（ SMD ）The plug-ins are also divided into HC-49U, HC-49S, HC-49SS tuning fork Type (cylindrical crystal oscillator). HC-49U is generally called 49U, some purchases are commonly called "high type", while HC-49S is generally called 49S, commonly called "short type", HC-49SS is generally called 49SS, commonly called (super short type, usually 2.5mm package height), tuning fork type can be divided into 3 * 9, 3 * 8, 2 * 6, 1 * 5, 1 * 4, etc. according to volume. Patch types are classified by size and foot position. For example, 7 * 5 (0705), 6 * 3.5 (0603), 5 * 3.2 (5032), etc. There are 4 pin and 2 pin feet. Oscillators can also be divided into plug-ins and patches. Plug ins can be classified by size and foot position. For example, the so-called full size is also called rectangle or 14pin, and the half size is also called square or 8pin. However, it should be noted that the 14pin and 8pin refer to the number of pins of the core IC inside the oscillator. The oscillator itself is 4pin. From different application levels, it can be divided into OSC (ordinary Chime ）、 TCXO (Warming the clock) VCXO (pressure control bell vibration) OCXO (Thermostatic bell) and so on. [1] The figure above shows Quartz resonator Of modality Spectrum, including fundamental mode, third-order Overtone , 5th order overtones and some spurious signal responses, namely parasitic modes. In oscillator application, the oscillator always selects the strongest mode to operate. Some interference modes have frequency temperature characteristics of sharp rise and fall. Sometimes, when the temperature changes, at a certain temperature, the frequency of the parasitic mode is consistent with the oscillation frequency, which leads to "decreased activity". When the activity decreases, the excitation of parasitic mode causes resonator The consumption of additional energy of, leads to the decrease of Q value, the increase of equivalent series resistance and the change of oscillator frequency. When the impedance increases to a considerable value, the oscillator will stop, that is, the oscillator will fail. When the temperature changes away from the temperature where the activity decreases, the oscillator will work again. The parasitic mode can be properly designed and controlled by packaging method. Constantly correct the size relationship between the electrode and the chip (that is, apply the energy trapping principle), and keep the main plane of the chip parallel, so that parasitic modes can be minimized. Nominal frequency: center frequency Or frequency Nominal value 。 Frequency accuracy: the deviation of the oscillator output frequency from the nominal frequency at room temperature (25 ℃± 2 ℃).
Adjust the frequency difference: within the specified temperature range, the maximum allowable value of the measured value when the oscillator output frequency is relative to 25 ℃ Frequency deviation 。 load resonant frequency (fL): Under the specified conditions, the crystal and Load capacitance Phase series or phase parallel connection When the combined impedance is resistive ( resonance ）One of the two frequencies of. When the load capacitance is connected in series, the load resonant frequency is the lower one of the two frequencies, and when the load capacitance is connected in parallel, it is the higher one of the two frequencies. Static capacitance: equivalent circuit The capacitance connected in parallel with the series arm in the, also called shunt capacitance, is usually expressed as C0. Operating temperature range: the temperature range that can ensure that the output frequency of the oscillator and its various characteristics meet the indicators.
Frequency temperature Stability : Under nominal power supply and load, the maximum allowable working temperature without implied reference temperature or with implied reference temperature within the specified temperature range frequency offset 。 ft=±（fmax-fmin)/(fmax+fmin)
ftref=±MAX[|(fmax-fref)/fref|，|(fmin-fref)/fref|]
Ft: frequency temperature stability (without implied reference)
Ftref: frequency temperature stability (with implied reference temperature)
Fmax: the highest frequency measured within the specified temperature range
Fmin: the lowest frequency measured within the specified temperature range
Fref: frequency measured at the specified reference temperature
Note: The production difficulty of crystal oscillator with ftref index is higher than that with ft index crystal oscillator Therefore, the crystal oscillator of the ftref index has a high price. Load capacitance : Determine load together with crystal resonant frequency The effective external capacitance of FL is expressed in CL. Load capacitor series: 8PF 12PF 15PF 20PF 30PF 50PF 100PF
Excitation level: the characteristic value of the power consumed by the crystal during operation. The optional values of excitation level are: 2mW, 1mW, 0.5mW, 0.2mW, 0.1mW, 50 μ W, 20 μ W, 10 μ W, 1 μ W, 0.1 μ W, etc
Aging rate: the relative change of output frequency within a certain time.
fundamental frequency : at the lowest order of vibration mode Vibration frequency 。 Overtone : Machinery for crystal vibration harmonic 。 The ratio of overtone frequency to fundamental frequency is close to but not integral multiple, which is the main difference between overtone frequency and electrical harmonic. Overtone vibration has three overtones, five overtones, seven overtones, nine overtones, etc. Quartz crystal resonators can be divided into HC-49U, HC-49U/S, HC-49U/S · SMD, UM-1, UM-5 and columnar crystals according to their different shapes and structures.
HC-49U is applicable to electronic products with wide space, such as communication equipment, television telephone 、 electronic toy Medium. HC-49U/S is applicable to all kinds of thin and small electronic equipment and products with limited space and height.
HC-49U/S · SMD is a quasi surface mount product, suitable for all kinds of ultra-thin, small computers and electronic equipment.
Cylindrical quartz crystal resonator is suitable for frequency stabilization and timing electronic products with narrow space, such as timer 、 Electronic clock , calculator, etc. UM series products are mainly used in mobile communication products, such as beeper , mobile phones, etc. Quartz crystal resonator is mainly used for frequency control and Frequency selection Circuit. This guide helps ensure that there are no unsatisfactory performance, inappropriate cost and poor availability. 1. Relation between vibration mode and frequency:
3 times Overtone 10～75MHz Five overtones 50 ～ 150MHz
Seven overtones 100 ～ 200MHz
Nine overtones 150 ～ 250MHz
2. Crystal resistance: for the same frequency, the resistance value when working at high overtone vibration will be greater than that when working at low overtone vibration.
"Signal source+level meter" function is controlled by network analyzer complete Ri, R0: internal resistance of the instrument: generally 50 Ω
R1 -- External impedance of filter input end, Impedance value Subtract 50 Ω from the matching impedance. R2 -- External impedance at the output end of the filter. The impedance value is the matching impedance minus 50 Ω.
In the matching impedance of filter conditions, sometimes there is a requirement for parallel connection capacitance, which should be connected according to the figure above.
3. Operating temperature range and temperature frequency difference: when proposing temperature frequency difference, the tolerance of temperature rise caused by equipment operation shall be considered. When the requirements for temperature frequency difference are very high, and space and power are both allowed, constant temperature operation should be considered, Thermostatic crystal oscillator It is designed for this purpose. 4、 Load capacitance And frequency traction: in many applications, a load reactance element is used to traction the requirements of crystal frequency, which can be found in the phase-locked loop circuit and frequency modulation It is very necessary in application. In most cases, the load reactance is capacitive. When the capacitance value is CL, it is relative to the load resonant frequency Offset: DL=C1/[2 (C0+CL)]. When CL is used as an adjustable component, the relative frequency traction is: DL1，L2= C1（CL1－CL2）/[2（C0+CL1）（C0+CL2）]。
5、 Load capacitance Selection of: crystal works in fundamental frequency The standard values of its load capacitance are 20PF, 30PF, 50PF, 100PF. and Overtone Crystals often work in Series resonance Where load capacitance is used, its load capacitance value shall be selected from the following standard values: 8PF, 12PF, 15PF, 20PF, 30PF. 6. Influence of excitation level: Generally speaking, the frequency change is positive when the excitation level of AT cut crystal increases. High excitation level will cause nonlinear effect , which may lead to parasitic oscillation; Severe thermal frequency drift; Over stress frequency drift and sudden change of resistance. When the excitation level is too low, the starting resistance will be difficult to overcome, the work will be poor and the index will be unstable. 7. Application in filter circuit: application in filter circuit In addition to the usual provisions, attention should be paid to the value and error of its equivalent circuit components as well as the position and amplitude of the parasitic response. Due to the particularity of the design of the filter crystal, the user should give special instructions when purchasing. [2] 
