The Composition and Design of Quartz Crystal Oscillator Circuit
The parallel and series are two kinds of common quartz oscillation circuit. The most intuitive difference between the two kinds of circuit is the appearance of resonator. The parallel crystal oscillator is in the form of parallel resonance, and the series crystal oscillator is in the form of series resonance.In order to better understand the basic principle and circuit design of crystal oscillator, we explain the basic characteristics of crystal material and the composition of quartz crystal oscillator circuit. I. Basic Properties of Crystal Materials The quartz crystal devices are widely used in frequency control and frequency selection circuits. The piezoelectric properties, elastic properties and strength properties of quartz are different according to the orientation of quartz. The performance of resonator made of quartz is also different. Now, dozens of useful cutting methods have been found. Quartz crystal can be deformed under the action of pressure and electric field. The deformation produced by pressure will simultaneously produce polarization, and the polarization intensity is proportional to the pressure. This phenomenon is called the positive piezoelectric effect. The deformation produced by electric field is also proportional to the electric field intensity, which is called the inverse piezoelectric effect. Quartz crystal has high mechanical strength, stable physical and chemical properties, and low internal loss. Among the common crystal materials with piezoelectric effect, quartz crystal is undoubtedly a tailor-made for wireless communication equipment. II. Composition and Design of Quartz Crystal Oscillator Circuit In order to make the crystal oscillator work more efficiently, the quartz oscillator circuit is usually composed of many components, such as capacitor, resistor, load, XTAL and PCB, which have different functions in the circuit. 1. Capacitor In circuit theory, capacitance is defined as the capacity of a capacitor to store electric charge when a specific voltage difference is applied.The selection of capacitors should be based on user requirements, choosing either chip-type or traditional-structure products. The NP0 series temperature coefficient products feature high frequency and low loss characteristics, making them suitable for a wide range of applications. 2. Resistance The size of the resistor is not necessarily better when smaller. The optimal choice is to balance the size with power consumption to meet the requirements of the oscillation circuit. 3. Load The oscillation circuit (excluding CRYSTAL) must exhibit negative resistance characteristics (as measured by a network spectrum analyzer). The absolute value of the negative resistance in the oscillation circuit must exceed three times the ESR/RR value of the CRYSTAL resistor (CRYS2TAL) for stable oscillation. 4. Quartz Resonator XTAL The crystal's dimensions and packaging should be precisely tailored to user requirements, with ATMODE recommended for resonators operating above 1MHz. 5. polychlorinated biphenyls The grounding method, whether large-area or point-type, should be designed according to the specific application. In high-frequency usage scenarios, it is essential to minimize the distributed parameters of the circuit. When necessary, attention should be paid to EMI protection.
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