(1) Nominal Frequency and Tolerance
The output frequency from the oscillating circuit with the right oscillation circuit matching is called the "nominal frequency".Frequency units are generally expressed in terms of megahertz (MHz) or Kilohertz (kHz).
In practical production and oscillation line applications, products at room temperature (25oC) will have some frequency dispersion error with respect to the center frequency.The maximum spread value of the allowable frequency error of this type is generally expressed in parts per million or % (percent).
(2) Fundamental and Overtone Vibrations Mode (Fundamental and Overtone Vibrations Mode)
The resonators of quartz crystal AT the AT cutting Angle mainly exist in the thickness shear oscillation mode.In the resonance of quartz crystal, besides the basic wave oscillation, the high-order octave resonance and the basic wave oscillation also exist between the electrode region of quartz crystal.However, since the electrode of the piezoelectric material vibrates in an electrically opposite phase environment, only an odd number of high-frequency octaves can occur, and even number octaves will not exist in the quartz crystal resonator.
(3) Load Capacitance (Load Capacitance, CL)
The "load capacitance" on the oscillator line is defined as the capacitance of the oscillator line seen from the two terminals of the quartz crystal resonator in other words, the load capacitance on the oscillator line.The load capacitor can be connected with the quartz crystal resonator in parallel or series on the line.In parallel oscillating lines, the load capacitance (Cl) affects the characteristics of the nominal frequency.The resonant frequency of this parallel line with load capacitance is expressed in fL.
(4) Frequency-temperature Stability
Quartz frequency changes with temperature, because the thermal expansion coefficient of the quartz material is different in each coordinate axis. As the temperature changes, the lattice spacing in each axial direction changes slightly.When different cutting angles are used, the variation of different oscillation modes will be different.
The design of the thickness shear oscillation mode AT the cutting Angle of the AT generally uses the frequency of 25 ° C as the reference temperature point to define the stability of frequency variation over the operating ambient temperature range.When defining the stability parameter of frequency against Temperature, the corresponding operating Temperature Range should also be specified.
The temperature stability of the quartz frequency module is measured in PPM or %, as is the nominal frequency error.The frequency and temperature characteristics of the components depend greatly on the cutting Angle, oscillation mode, surface treatment and shape size of the quartz.In addition, the characteristics of load capacitance (CL) and drive power (drive level) on the oscillation line will also affect the stability of the output frequency of the oscillation line against temperature changes.
(5) Equivalent Series Resistance (ESR)
When the quartz crystal oscillates in series at FS, C1 and L1 are in opposite phases and cancel each other out. The admittance of the entire motional arm of the resonator is close to the minimum impedance value R1.In this case, the resonator of the whole quartz crystal is only a resistive component, and the resistance value R1 is the mechanical energy loss of the whole component.It contains the quartz material, and then all the energy loss on the material and the packaging material.
(6) Dynamic Capacitance (Motional capacitance-C1) and dynamic Inductance (Motional Inductance L1) in capacitance-C1
In Formula 1, the dynamic capacitor C1 and the dynamic inductance L1 are correlated with the series frequency of the parallel vibration, FS.
In the actual measuring system, we only measure the dynamic capacitance C1 and the series co-vibration frequency FS.The dynamic inductance L1 is calculated by Equation (4).
(7) Static Capacitance (Static Capacitance or Shunt Capacitance, CO)
The static capacitance, CO, mainly comes from the capacitor formed by the quartz chip as dielectric material and two electrodes.Another small portion of the static capacitance comes from the capacitance between the quartz chip and the conductive material of the wiring and the capacitance of the packaging case.
The static capacitance is measured at a range well below the oscillation frequency to avoid being affected by the dynamic capacitance near the oscillation frequency.Equation (5) is the mathematical expression of static capacitance.
(8) Drive power (Drive Level)
The driving power of quartz crystal refers to the power consumed by the resonator of quartz crystal, which is generally expressed in microwatt.The oscillator circuit must be designed to provide the right amount of power for the quartz crystal resonator to start and continue oscillating.The oscillation of quartz crystal is a physical high-frequency mechanical vibration. The electrical impedance value of the oscillation is about 10~100 ohms below (depending on the frequency range and size).Excessive driving power provided by the oscillator circuit will cause the nonlinear characteristics of the quartz crystal and the quartz/electrode/subsequent material interface to deteriorate, resulting in excessive changes in the oscillation frequency FL and equivalent impedance R1.Quartz crystals will be unstable when they work under excessively high driving power for a long period of time. With the low power consumption demand of various application surfaces and the trend of small shape of products, coupled with the substantial improvement of quartz products' technology in recent years, the electrical impedance value of quartz crystal resonators will decrease and be stable as a whole.The oscillator circuit design does not need to, and should not, provide excessive driving energy on the quartz crystal resonator.For most applications, the oscillator line provides a maximum power of 10 to 100 microwatt (depending on the size and frequency of the quartz resonator) for the quartz resonator, which is sufficient.
(9) Quality Factor (Q)
For quartz crystal resonators, the electrical mass factor Q is a very important characteristic. The mass factor of quartz crystal resonators can reach several million or more.
Pullability and Trim Sensitivity
Quartz crystal resonators are used in parallel oscillating circuits, and the oscillation frequency has a great relationship with the load capacitance Cl.Is the variation curve of FL frequency relative to load capacitance Cl on parallel oscillating circuit.
The "pull rate" of the frequency refers to the frequency change from the frequency FL1 of the load capacitor CL1 to the frequency FL2 of the load capacitor CL2.Can be the value of the frequency change between FL1(Cl =24pF) and FL2(Cl =10pF).In this example, the frequency traction rate is 220 PPM. If we minimize the load capacitance values of CL1 and CL2 (the curve is differentiated mathematically), we get the tangent value of the curve.The value of the tangent is the trim sensitivity of the load capacitance.
The frequency sensitivity of Cl =24 pF is 10 PPM /pF, and that of Cl =10 pF is 20 PPM /pF.In parallel circuits, the smaller the load capacitance, the more sensitive the frequency is to changes in the load capacitance.On the contrary, the higher the load capacitance, the less sensitive the frequency is to changes in the load capacitance. This is the case when quartz crystal resonators are used on VCXO lines, the line design will select a smaller load capacitance.On the contrary, when more accurate frequency signal is required, the line design will choose a higher load capacitance.
(11) Aging
The name "aging" means that in a certain period of time, the frequency of quartz crystal resonators changes with time, with parts per million (PPM) as the unit.The characteristic curve of aging in terms of frequency and time is usually exponential.The maximum frequency aging variation occurred during the first month after the quartz frequency module was manufactured. After that, the frequency variation gradually decreased with time.There are several major factors affecting the aging characteristics of frequency, such as packaging method, type of material, process temperature, process control, heat treatment process, and product size and frequency.Most specifications define short-term (1~3 months) or long-term (1~10 years) frequency aging requirements.
(12) Storage TEMPERATURE RANGE
In addition to the previous ambient Temperature Range, another temperature-related feature is the "Storage Temperature Range".This parameter refers to the maximum and minimum temperature range at which the product can be stored under static conditions.Within this temperature range, the product must be kept in the operating temperature range for a long period of time and conform to the specifications.This property is very important to the design of the components and manufacturing process of quartz crystal resonators, so it should be carefully defined.
(13) Negative Resistance (-R)
The negative impedance refers to the impedance characteristic value of the oscillator circuit at the oscillation frequency encountered from the two terminals of the quartz crystal resonator looking at the oscillator circuit.A sufficient amplification gain value must be provided on the oscillator circuit to compensate for the mechanical energy loss of the quartz crystal resonator.Negative impedance is not a product parameter of quartz oscillator, but an important characteristic parameter of oscillator circuit.From the perspective of the resonator, it is the "negative impedance" in the oscillating circuit.(1) Nominal Frequency and Tolerance
The output frequency from the oscillating circuit with the right oscillation circuit matching is called the "nominal frequency".Frequency units are generally expressed in terms of megahertz (MHz) or Kilohertz (kHz).
In practical production and oscillation line applications, products at room temperature (25oC) will have some frequency dispersion error with respect to the center frequency.The maximum spread value of the allowable frequency error of this type is generally expressed in parts per million or % (percent).
