What are Resonators?

Catalog

I. Types

1. Quartz crystal resonator

Quartz crystal resonators use the piezoelectric effect of quartz crystals (applying mechanical force to certain dielectrics to cause the relative displacement of the positive and negative charge centers inside them, resulting in polarization, resulting in the appearance of bound charges with opposite signs on the surfaces of both ends of the medium. Within a certain stress range, the mechanical force and the charge have a linear and reversible relationship.) The resonant component is made.

Diagram of how quartz crystal resonators work 

1.1 Working Principle

A crystal refers to a solid in which atoms, molecules, or ions extend in all directions in a regular and repetitive pattern.

Crystals and almost all elastic materials have a natural resonance frequency, which can be used through appropriate sensors. For example, steel has good elasticity and a fast speed of sound. Before quartz crystal was widely used, steel was used as a mechanical filter. The resonance frequency depends on the crystal size, shape, elasticity, and speed of sound in the substance. Crystals for high frequency are usually cut into simple shapes, such as square slices. Typical low-frequency crystals are often cut into tuning fork shapes, such as those used in watches. If too high accuracy is not required, ceramic resonators can also be used instead of quartz crystal resonators.

When the electrodes on the quartz crystal are used to apply an electric field to a properly cut and placed quartz crystal, the crystal will deform. This is the reverse piezoelectric effect. When the applied electric field is removed, the quartz crystal will return to its original shape and emit an electric field, thus generating a voltage on the electrode. Such characteristics cause quartz crystals to behave in a circuit similar to an RLC circuit formed by a combination of inductors, capacitors, and resistors. The resonance frequency of the inductor and capacitor in the combination reflects the physical resonance frequency of the quartz crystal.

The advantage of a quartz crystal is that when the temperature changes, the elastic coefficient, and size that affect the oscillation frequency change slightly, so the frequency characteristics are stable. The characteristics of resonance also depend on the cutting angle between the vibration mode and the quartz (relative to the crystal axis). At present, AT cutting is commonly used, and its oscillation is the thickness-shear oscillation mode. In addition, in strict occasions requiring high precision and stability, quartz crystals will be placed in a constant temperature box and a vibration-absorbing container to prevent interference from external temperature and vibration.

1.2 Pros and Cons

Advantages: The signal level is variable, that is to say, it is determined according to the oscillating circuit. The same crystal can be applied to a variety of voltages, can be used for a variety of chips with different clock signal voltage requirements, and the price is usually lower. . The accuracy of the crystal resonator is 1PPM (parts per million) to 100PPM.

Disadvantages: The crystal resonator is a non-polar component with 2 pins. It needs the help of a clock circuit to generate an oscillating signal, and it cannot oscillate by itself. Compared with crystal oscillators, the defect of crystal resonators is that the signal quality is poor. It usually needs to accurately match the peripheral circuits (capacitors, inductances, resistances for signal matching, etc.). When replacing crystals with different frequencies, the peripheral configuration circuits need to be done accordingly. Adjustment.

The crystal resonator has some equivalent parameters, and different use environments may have different requirements. When selecting, the environment temperature, load capacitance, frequency accuracy, and other requirements must be considered. This requires some control of the parameters of the peripheral oscillator circuit for a stable frequency to be output.

2. Ceramic resonator

A ceramic resonator is a piezoelectric ceramic device used to oscillate at a specific frequency. The materials used to manufacture such devices excite resonance characteristics during the production process. Because this resonance characteristic is within the production error range, and its quality factor is much lower than that of quartz, the frequency stability that ceramic resonators can provide is not as good as crystal resonators. Generally, ceramic resonators are used on occasions with low cost and low-performance requirements.

Advantages: Compared with crystals, the cost of ceramic resonators is only half that of crystals and the size is smaller.

Disadvantages: Compared with crystals, it lacks frequency and temperature stability. Its accuracy is poor, probably between 1% and 0.1%.

The typical initial accuracy of ceramic resonators is in the range of 0.5% to 0.1%, and drift caused by aging or temperature changes may change this accuracy range. The tolerances of inexpensive ceramic resonators are only ±1.1%, and the accuracy of higher-end automobiles is ±0.25% and ±0.3%, respectively. The future application lies in the automotive CAN (controller area network) bus application, with an operating temperature of -40°C to +125°C. Low-cost ceramic resonators with frequencies ranging from 200 KHZ to about 1 GHZ are suitable for embedded systems that do not have strict timing requirements. Ceramic devices start quickly and generally have smaller volumes than quartz devices. They are also more able to withstand shock and vibration.

The difference between ceramic resonators and quartz resonators lies in accuracy and temperature stability. Quartz crystals have higher accuracy and better temperature stability than ceramic crystals. The accuracy of the quartz crystal can reach six digits after the decimal point, and the unit is expressed in ppm (parts per million). For example, the error of the 4M and 11.0592M quartz crystals you use is generally less than +/-30ppm, that is, the accuracy is between 30 parts per million. The accuracy of ceramic resonators can only meet three decimal places, which is expressed in khz. For example, the accuracy of 4MHz ceramic resonators is generally +/-750kHz.

In terms of technical parameters, quartz resonators can replace ceramic resonators, but ceramic resonators may not be able to replace quartz resonators. Ceramic resonators are mostly used in TV remote controls, toy products, and other products that do not require high precision. Quartz resonators are needed where precision is required in consumer electronic products such as instrumentation, communications, and communications.

II. Characteristics

The main characteristic parameters of resonators include nominal frequency, adjustment frequency difference, temperature frequency difference, equivalent resistance, excitation level, load capacitance, static capacitance, aging rate, and temperature range.

①Nominal frequency: under specified conditions, the specified resonance center frequency of the resonator.

②Adjust the frequency difference: under the specified conditions, the maximum deviation value of the operating frequency at the reference temperature from the nominal frequency.

③Temperature frequency difference: The allowable deviation of the operating frequency from the reference temperature in the entire operating temperature range under specified conditions.

④ Reference temperature: the specified ambient temperature when measuring the parameters of the quartz crystal resonator. For constant-temperature quartz crystal resonators, it is generally the center point of the operating temperature range; for non-temperature-controlled quartz crystal resonators, it is 25°C±2°C.

⑤Load resonance resistance: the resistance value of the quartz crystal resonator in series with the specified external capacitor at the load resonance frequency.

⑥ Excitation level: refers to the effective power consumed when the quartz crystal resonator is working, and it is a measure of the excitation state applied to the quartz crystal element. Commonly used standard values are 0.1mW, 0.5mW, 1mW, 2mW and 4mW. In actual use, the excitation level can be adjusted. When the excitation is strong, it is easy to start to vibrate, and when the excitation is too weak, the frequency stability becomes worse or even no vibration.

⑦Load capacitance: refers to the effective external capacitance that determines the resonant frequency of the load together with the quartz crystal resonator. Commonly used standard values of load capacitance are 16pF, 20pF, 30pF, 50pF and 100pF. The load capacitance can be adjusted appropriately according to the specific situation. Generally, the working frequency of the resonator can be adjusted to the nominal value through adjustment.

⑧Static capacitance: the static capacitance between the two pins of the quartz crystal resonator.

⑨Aging rate: refers to the error caused by the aging of the quartz crystal with the increase of time.

⑩Temperature range: refers to the allowable range of ambient temperature changes in working conditions.

III. Applications

Dielectric resonator

As early as 1939, the concept and theory of dielectric resonators had been proposed. However, because no suitable dielectric materials were found, this theory was not in practice for more than 20 years. By the 1960s, rutile porcelain and other high dielectric constants The successful development of ceramics (ε≈80100) made the dielectric resonator start to be noticed again. But because the temperature coefficient of rutile porcelain is too high, it limits its practical application. In the 1970s, barium titanate and zirconium titanate ceramics were developed. Their high dielectric rate, low loss, and low-temperature coefficient made dielectric resonators practical. Dielectric resonators have the advantages of small size, lightweight, high-quality factor, and good stability. In particular, it is easy to be applied to microstrip circuits or microwave integrated circuits and millimeter-wave bands, which have received great attention and developed rapidly. When the dielectric rate is high, the interface between the medium and the air is similar to an open road, and the emission coefficient of electromagnetic waves at the interface is close to 1. At this time, the surface of the dielectric resonator can be regarded as an open circuit wall, that is, a magnetic wall. Therefore, the dielectric resonator becomes a closed system with homogeneous boundary conditions, that is, an equivalent open wall (magnetic wall) resonant cavity.

Other uses

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 appearance structures.

HC-49U is suitable for electronic products with wide space, such as communication equipment, televisions, telephones, and electronic toys.

HC-49U/S is suitable for all kinds of thin and small electronic devices and products whose space height is restricted.

HC-49U/S·SMD is a quasi-surface-mount product, suitable for all kinds of ultra-thin, small computers and electronic equipment.

Columnar quartz crystal resonators are suitable for frequency-stabilized timing electronic products such as timers, electronic clocks, calculators, etc. in a small space.

UM series products are mainly used in mobile communication products, such as BP machines, mobile phones, etc.