ProductiveCrystal oscillatorIt has the function of self-loading capacitor, and needs external capacitor when it is practical on the line, so it will makeCrystal oscillatorThe accuracy is more precise. There are also many IC in use.Crystal oscillatorWhen the outside does not need capacitors, but this product is generally not very strict requirements, but the use of merchants to be very like. Electrically, it can be equivalent to a capacitor and a resistor in parallel and then a capacitor in series. In electrotechnics, this network has two resonance points. The lower frequency is series resonance, the higher frequency is parallel resonance. Because of the characteristics of crystal itself, the distance between the two frequencies is very close. In this very narrow frequency range, crystal oscillator is equivalent to an inductance. So long as the two ends of crystal oscillator are connected in parallel with the appropriate capacitors, it will form a parallel resonant circuit. The parallel resonant circuit can be added to a negative feedback circuit to form a sinusoidal oscillator circuit. Because the frequency range of crystal oscillator equivalent to inductance is very narrow, the frequency of the oscillator will not change greatly even if the parameters of other components vary greatly.
Crystal oscillatorThere is an important parameter, that is, the value of the load capacitance, choose the parallel capacitance equivalent to the value of the load capacitance, you can get the nominal resonance frequency. In general, crystal oscillator oscillator circuit is connected to the crystal oscillator at both ends of an inverted amplifier (note that the amplifier is not a inverter), and then two capacitors are connected to the two ends of the crystal oscillator respectively. The other end of each capacitor is connected to the ground again. The capacitance value of the two capacitors in series should be equal to the load capacitance. There is equivalent input capacitance, which can not be ignored.
In general, the load capacitance of crystal oscillator is 15p, 20pF or 12.5p. If the equivalent input capacitance of element pin is considered, the oscillation circuit composed of two 22P capacitors is a better choice.
Crystal oscillator is a component that provides frequency reference for circuit. It is usually divided into active crystal oscillator and passive crystal oscillator. Passive crystal oscillator needs oscillator in the chip. The signal voltage of crystal oscillator is determined according to the starting circuit, and different voltage is allowed. But passive crystal oscillator usually has poor signal quality and precision, so it needs accurate matching. Peripheral circuit (inductance, capacitance, resistance, etc.), if need to replace the crystal oscillator at the same time to replace the peripheral circuit. Active crystal oscillator does not need the internal oscillator of chip, it can provide high-precision frequency reference, and the signal quality is better than passive crystal oscillator.
The Manual of each chip will provide a standard circuit with external crystal oscillator input, indicating the highest usable frequency of the chip and other parameters, which should be mastered in circuit design. Unlike the CPU used in computers, the crystal oscillator frequencies that single-chip computers can receive are relatively low, but sufficient for general control circuits.
Crystal oscillator is also divided into two types: passive crystal oscillator and active crystal oscillator. The passive crystal oscillator is different from the active crystal oscillator in English. The passive crystal oscillator is called crystal and the active crystal oscillator is called oscillator. The passive crystal oscillator needs the help of clock circuit to produce oscillation signal, so it can not oscillate itself, so the term "passive crystal oscillator" is not accurate; the active crystal oscillator is a complete resonant oscillator.
Resonant oscillators include quartz (or its crystal material) crystal resonators, ceramic resonators, LC resonators, etc. Crystal oscillator and resonant oscillator have their common active crystal resonant oscillators.
The reason why a quartz wafer can oscillate is based on its piezoelectric effect. Physically, if an electric field is applied between the two plates of the wafer, the crystal will deform mechanically; otherwise, if a mechanical force is applied between the plates, an electric field will be generated in the corresponding direction. This phenomenon is called piezoelectric effect. If alternating voltage is added between the plates, mechanical deformation vibration will occur, and mechanical deformation vibration will produce alternating electric field. Generally speaking, the amplitude of this mechanical vibration is relatively small, and its vibration frequency is very stable. But when the frequency of the applied alternating voltage is equal to the natural frequency of the wafer (depending on the size of the wafer), the amplitude of the mechanical vibration will increase sharply. This phenomenon is called piezoelectric resonance, so the quartz crystal is also called quartz crystal resonator. It is characterized by high frequency stability.
Quartz crystal oscillator and quartz crystal resonator are electronic devices that provide stable circuit frequency. The quartz crystal oscillator is excited by the piezoelectric effect of the quartz crystal, and the quartz crystal resonator is operated by the combination of the quartz crystal and the built-in IC. The oscillator is directly applied to the circuit. When the resonator works, it is usually necessary to provide 3.3V voltage to maintain the work. An important technical parameter of the oscillator is resonance resistance (RR), which has no resistance requirement. The size of RR directly affects the performance of the circuit, and it is also an important parameter for every business to compete. The crystal oscillator meets the market IC and matches the line demand. The conventional frequency point and load capacitor can be specified specially. The custom-made crystal oscillator can absolutely meet the development of electronic and digital products in the market.