Parameters of crystal oscillator and Crystal

1. Differences between crystal oscillator and Crystal Oscillator

1)Crystal OscillatorIt is short for the source crystal oscillator, also known as the oscillator. The English name is oscillator.CrystalsIt is short for passive crystal oscillator, also called a resonator. English name: Crystal.
2)Passive crystal oscillator (crystal)Generally, it is a non-polar element directly inserted with two feet. It must use a clock circuit to generate an oscillating signal. Common packages include 49u and 49s.
3)Active crystal oscillator (Crystal Oscillator)Generally, the table is encapsulated with four feet. There is a clock circuit inside, and only the power supply can generate an oscillating signal. It is generally divided into 7050, 5032, 3225, and 2520 encapsulation forms.

2. Difference Between MEMS silicon crystal oscillator and Z Crystal Oscillator
MEMS silicon crystal oscillator is made of silicon as raw material and advanced semiconductor technology. Therefore, in terms of high performance and low cost, it has obvious advantages over Z, as shown in the following aspects:
1) fully automated semiconductor technology (chip-level), no air tightness problems, never stop vibration.
2) The internal includes a temperature fill circuit, no temperature drift,-40-85 deg C full temperature assurance.
3) the average working time without faults is 0.5 billion hours.
4) the seismic performance is 25 times higher than that of the Z oscillator.
5) supports any frequency point of 1-MHz, accurate to 5 digits after the decimal point.
6) it supports 1.8 V, 2.5 V, 2.8 V, and 3.3v operating voltage matching.
7) supports precision matching of 10ppm, 20ppm, 25ppm, 30ppm, and 50ppm.
8) All standard sizes of 7050, 5032, 3225, and 2520 are supported.
9) The standard quad-pin and six-pin packages directly replace the Z oscillator without any design changes.
10) Differential output, single-ended output, vcxo, and tcxo are supported.
11) the market growth rate of 300% is expected to replace the market of more than 80% Z Oscillator in three years.

3. Equivalent Circuit of the Crystal Resonator

Is a crystal resonator with the same resonance frequencyImpedanceSimplified Circuit of features. Among them, C1 is a dynamic capacitor or equivalent series capacitor; L1 is a dynamic inductor or equivalent series inductor; R1 is a dynamic resistor or equivalent series resistor; c0 is a static capacitor, also known as an equivalent parallel capacitor.

This equivalent circuit has two most useful zero-phase frequencies, one being the resonant frequency (FR) and the other being the anti-resonant frequency (FA ). When a crystal element is actually used in an oscillating circuit, it is usually connected with a load capacitor to work together to make the crystal work at a certain frequency between FR and Fa, this frequency is determined by the phase of the oscillating circuit and the effective impedance. By changing the circuit's impedance conditions, the crystal frequency can be adjusted within a limited range.

4. Key Parameters

4.1 nominal frequency

It refers to the frequency specified in the crystal element specification, that is, the ideal operating frequency that the user wants in circuit design and component selection.

4.2 adjustment frequency difference

The maximum allowable deviation between the operating frequency and the nominal frequency at the reference temperature. Usually expressed in ppm (1/106.

4.3 Temperature Difference
Allowable Deviation between the operating frequency within the entire temperature range and the operating frequency of the benchmark temperature. Usually expressed in ppm (1/106.

4.4 Aging Rate
It refers to the frequency drift caused by time under specified conditions. This indicator is necessary for precision crystals, but it "does not have clear test conditions, but is continuously monitored by the manufacturer through planned sampling of all products, some crystal elements may be less efficient than the specified level, which is acceptable "(according to IEC announcement ). The best solution to aging problems is to rely on close negotiation between manufacturers and users.

4.5 Resonant Resistance (RR)
It refers to the equivalent resistance of the crystal element at the resonant frequency. When the effect of C0 is not considered, it is also similar to the dynamic resistance r1 of the so-called crystal or equivalent series resistance (ESR ). This parameter controls the quality factor of the crystal element, and determines the crystal oscillator level in the applied circuit, thus affecting the stability of the crystal so that it can be ideal for vibration. Therefore, it is an important indicator parameter of the crystal element. Generally, the smaller the selection of crystal boxes for a given frequency, the higher the average value of ESR. In most cases, the resistance value of a specific crystal element cannot be predicted during the manufacturing process, however, the resistance must be lower than the maximum value given in the specification.

4.6 load resonance resistance (RL)
The resistance of the crystal element in connection with the specified external capacitor at the load resonance frequency FL. For a given crystal element, the load resonance resistance value depends on the load capacitance value working with the element. The resonance resistance after the load capacitance is attached to the string is always greater than the resonance resistance of the crystal element.

4.7 load capacitance (CL)
Together with the crystal element, determine the effective external capacitance of the load resonant frequency FL. CL in the crystal element specification is a test condition and a use condition. This value can be adjusted based on your actual usage, to fine tune the actual operating frequency of FL (that is, the manufacturing tolerances of the crystal can be adjusted ). However, it has an appropriate value, otherwise it will lead to deterioration of the oscillating circuit. The value is usually 10pf, 15pf, 20pf, 30pf, 50pf, or else, when the CL mark is "listen", it indicates that it is applied in a series resonant circuit. Do not add a load capacitor, and the operating frequency is the crystal (series) resonant frequency Fr. Users should note that for some crystals (including non-encapsulated vibrator applications), ± 0 under a fixed load capacitor (especially for small load capacitors) in a production specification. the deviation of the actual capacitance of the 5pf circuit can produce a frequency error of ± 10 × 10-6. Therefore, the load capacitor is a very important specification for ordering.

4.8 static capacitor (C0)
The capacitance in the static arm of the equivalent circuit. Its size mainly depends on the electrode area, wafer thickness and wafer processing technology.

4.9 dynamic capacitance (C1)
The capacitance in the dynamic arm of the equivalent circuit. Its size mainly depends on the electrode area, and also depends on the chip parallelism and fine-tuning volume.

4.10 dynamic inductance (L1)
Inductance in the dynamic arm of the equivalent circuit. Dynamic inductance and dynamic capacitance are related to each other.

4.11 resonance frequency (FR)
It refers to the lower of the two frequencies in which the electrical impedance of the crystal element is resistance under the specified conditions. Based on the equivalent circuit, when the function of C0 is not taken into account, FR is determined by C1 and L1, which is approximately equal to the so-called series (Branch) resonance frequency (FS ). This frequency is the natural resonance frequency of the Crystal. In the design of the high-stability crystal oscillator, it is a design parameter used to make the crystal oscillator work stably at the nominal frequency, determine the frequency adjustment range, and set the frequency fine-tuning device.

4.12 load resonance frequency (FL) 
It refers to one of the two frequencies when the combination impedance of a crystal element is displayed as resistance in series or in parallel with a load capacitor under specified conditions. When the series load capacitor is used, FL is the lower of the two frequencies; when the parallel load capacitor is used, FL is the higher of the two frequencies. For a given load capacitance value (CL), the actual effect is that the two frequencies are the same.
This frequency is the actual frequency in the circuit when the majority of crystals are used. It is also the Testing Index parameter of the manufacturer to meet the user's requirement for the product to meet the nominal frequency.

4.13 quality factor (q)
Quality Factor, also known as mechanical Q value, is an important parameter that reflects the performance of the resonator. It has the following relationships with L1 and C1:
Q = wl1/R1 = 1/wr1c1
In the above formula, the larger the R1, the lower the Q value, the larger the power dissipation, and the unstable frequency. The higher the Q value, the more stable the frequency.

4.14 level of drive)
It is a measure of the excitation conditions applied to crystal elements, expressed in the form of dissipation power. The frequency and resistance of all crystal elements change with the excitation level to some extent, which is called the excitation level correlation (DLD ), therefore, the excitation level in the ordering specification must be the excitation level in the actual application circuit of the crystal. Because of the inherent excitation level correlation characteristics of crystal elements, when you design the oscillator circuit and use the crystal, it is important to note and ensure that there is no phenomenon of low incentive level resulting from poor vibration or abnormal frequency of excessive incentives.

4.15 incentive level correlation (DLD)
Due to the piezoelectric effect, the excitation level forces the harmonic oscillator to produce mechanical oscillation. In this process, the acceleration work is converted into kinetic energy and elastic energy, and the power consumption is converted into heat. The conversion of the latter is caused by the friction between the interior and exterior of the Z harmonic oscillator.
Friction Loss is related to the speed of the Vibration Particle. When the shock is no longer linear, or when the tension, strain, displacement, or acceleration of the inner or its surface and installation Points reach critical, friction Loss will increase. This causes changes in frequency and resistance.
The main cause of poor DLD during processing is as follows. The result may be that it cannot be affected:
1) particle contamination on the surface of the harmonic oscillator. The main cause is that the production environment is not clean or the wafer surface is illegally exposed;
2) mechanical damage to the harmonic oscillator. The main cause is the scratches generated during the grinding process.
3) particles or silver balls exist in the electrode. The main reason is that the vacuum chamber is not clean and the coating rate is not suitable.
4) mounting is poor contact with electrodes;
5) there is a mechanical stress between the bracket, electrode and the quartile.

4.16 dld2 (unit: OHM)

The difference between the maximum and minimum values of the load resonance resistance at different excitation levels. (For example, from 0.1uw ~ 200uw, 20 steps in total ).

4.17 RLD2 (unit: OHM)

The average value of the load resonant resistance at different excitation levels <is close to the value of the Resonant Resistance RR, but is larger>. (For example, from 0.1uw ~ 200uw, 20 steps in total ).

4.18 parasitic response
All Crystal elements have other frequency responses in addition to the primary response (required frequency. The method to reduce the parasitic response is to change the chip's geometric size, electrode, and wafer processing technology, but it also changes the dynamic and static parameters of the crystal.

Parasitic Response Measurement
1) SPDB uses dB to indicate the difference between the FR amplitude and the maximum parasitic amplitude;

2) spur's resistance at the maximum parasitic position;
3) the distance between the minimum resistance parasitic and resonance frequency of spfr, expressed in Hz or ppm.

5. Classification of Crystal Oscillator

5.1 package Z oscillator (spxo)

A Z Oscillator with no temperature control or temperature compensation. The frequency and temperature characteristics depend on the stability of the Z oscillating crystal.
5.2 temperature compensated Z oscillator (tcxo)
The temperature compensation circuit is added to reduce the frequency of the Z oscillator that changes due to the surrounding temperature.

5.3 Voltage Controlled Z oscillator (vcxo)

A Z oscillator that controls external voltage and enables the output frequency to change or adjust.
5.4 thermostatic grooz oscillator (ocxo)

Maintain a Z oscillator or a Z oscillator at a certain temperature in a constant temperature tank, and control its output frequency to maintain a very small variation in the surrounding temperature.

In addition to the above four kinds of oscillator, along with the application of PLL, digital, memory technology, the diversified Z Oscillator with other functions also rapidly increased.