Resonators and Generators
(246)What are resonators, resistors, and cristal oscillators?
A quartz resonator is an electronic device, which is used to keep track of time with high precision. This accuracy is due to the electric pulses generated at equal intervals. This phenomenon is referred to as fixed clock rate. Resonators are used, among others in microcontroller development boards, computers, TV remote controls, toys, watches and many other commonly used electronic equipment. Quartz resonators are also commonly known as quartz crystals, but you can also meet terms such as quartz resistor or quartz oscillator.
Resonator types
There are several types of resonators. The most popular of these are quartz resonators, but there are alsoceramic resonators, and the increasingly popular silicon resonators. The quartz resonators used in watches are a special variety of resonators (oscillators).
Quartz crystal resonators. made of a precisely cut quartz crystal, i.e. silicon dioxide (SiO2), have two leads. They are attached to metal electrodes. The different natural frequency of the resonator is achieved by the different shape and size of the quartz used. Ceramic resonators have a similar structure, but their main element is a piezoelectric material other than quartz.
Quartz resonators use the piezoelectric effect, which is the ability of certain materials to generate an electric charge in response to applied mechanical stress (the ends of the crystal become electrically charged). Piezoelectric material also exhibits the reverse piezoelectric effect. When a voltage difference is applied to its ends, it deforms. The quartz resonator connected to an electronic circuit causes it to vibrate; by supplying energy to the circuit, it generates a mechanical resonance with a frequency equal to the natural frequency of the used quartz crystal. The most common type of electronic oscillator is the Pierce oscillator.Sometimes you can find ready-made modules in the form of pulse generators. They have on-board electronics and usually 4 leads, which are responsible for ground and power supply, pulse output and control input.
Quartz resonator properties - accuracy and frequency
he accuracy of quartz resonators is determined by a unit called PPM (parts per million). For example, 1% accuracy is equal to 10 000 PPM. It is particularly important, among other things, in high quality watches so that these do not lose or gain a few seconds per day. Quartz resonators have the highest accuracy with an average of several tens of PPM, which in practice means a range of roughly 3 to 100 PPM. Currently manufactured ceramic resonators have very similar stability, starting at around 10 PPM, while quartz resonators used in watches do not exceed 20 PPM.
Please note that the accuracy and stability of the pulses generated by crystal resonator are highly dependent on temperature. Thus, constant temperature crystal oscillators are available; this is possible thanks to an additional electronic circuit. It is interesting to note that the frequency of the pulses generated by a resonator can even be affected by its spatial orientation relative to the gravity vector, as the force of the Earth's attraction can to some extent alter he frequency of natural vibrations of the crystal.
Of course, in addition to accuracy, the frequency is equally important with quartz resonators. This value can range from tens of kilohertz[kHz] to tens of megahertz [MHz]. The quartz resonators used in watches could be the most interesting here, as they will have a frequency of 32 768 kHz in virtually every case. This is due by the fact that when you divide this value by two to the power of fifteen, you get a pulse once per second, the time base of an analogue clock.
Quartz resonator parameters
The frequency of the resonator is usually stamped on the package. Unfortunately, like most devices, quartz resonators can change their frequency characteristics to some degree over time due to aging.
Selection of quartz crystal resonators
Quartz crystal oscillators, like virtually any other electronic component, are available in THT or SMD packages.
When choosing a quartz resonator, the pitch of the resonator, affecting mechanical compatibility, should be taken into account. The term is used to describe the distance between the leads of electronic components, e.g., integrated circuits or terminal blocks. The standard pitches for quartz resonators are 0.7mm, 1.1mm, 2.54mm, 4.88mm, and 5.1mm.
The most common package types for quartz crystal oscillators are cylindrical packages (HC-49, HC-49-S, HC-49/U, TC26, and TC38) which are THT (through-hole mounting) packages, and HC-49SM and HC-49SMD (SMD, surface mounting).
Attention can also be paid to a number of other parameters, such as the operating temperature, which can range from about -55°C to 150°C, power, given in milliwatts[mW] or even nanowatts [nW], but also the capacitance, which can range from about 6 pF (picofarad) to 30 F.
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