Understand the structure and function of quartz crystal oscillator

Quartz crystal oscillator is commonly known as crystal oscillator. It is a kind of resonant device made by piezoelectric effect of quartz crystal (silica crystal).The basic structure is as follows: slice a piece of quartz crystal at a certain azimuth (called a wafer, which can be square, rectangular or round) and apply it to two corresponding surfaces.The silver layer ACTS as the electrode, and a lead wire is welded on each electrode to connect to the pin, and the encapsulation shell is added to form the quartz crystal resonator, referred to as the quartz crystal or crystal, referred to as the crystal oscillator.The crystal element of an oscillating circuit composed of IC is called a crystal oscillator.The product is usually packaged in a metal case, but can also be packaged in a glass case, ceramic or plastic.

Structure of quartz crystal oscillator

The crystal oscillator body is an anisotropic crystal.It is made of wafers cut at a specific azimuth and coated with silver on the corresponding surface of the wafer.A pair of metal blocks are mounted as plates to form a quartz crystal oscillator.The reason why quartz crystals can be used as oscillating circuits is because of their piezoelectric effect.When an electric field is applied between two plates on the outside of the wafer, the crystal will deform mechanically.Conversely, when mechanical forces are applied between plates, an electric field is generated in the crystal.This phenomenon is called the piezoelectric effect.

Piezoelectric effect

If an electric field is added to the two electrodes of a quartz crystal, the chip undergoes mechanical deformation.Conversely, if mechanical pressure is applied on either side of the wafer, an electric field is generated in the corresponding direction of the wafer.This physical phenomenon is called the piezoelectric effect.If an alternating voltage is applied to both poles of the wafer, the wafer will produce mechanical vibration, and the mechanical vibration of the wafer will produce an alternating electric field.Generally speaking, the amplitude of mechanical vibration and alternating electric field of the chip is very small, but when the frequency of applied alternating voltage is a certain value, the amplitude obviously increases, far more than other frequencies.This phenomenon is called piezoelectric resonance, which is very similar to the resonance phenomenon of LC circuit.The resonant frequency depends on the cutting mode, the geometry and size of the chip.

The function of a quartz crystal oscillator

Quartz crystal oscillator (PXO) is widely used in the system frequency source, navigation and other communication fields of ordinary quartz crystal oscillator (PXO), operating frequency range of 1MHz to 150MHz, frequency stability of 25ppm, 50ppm and 100ppm, output rise and fall time of 5ns, the aging rate of 5ppm/ year.

There are also SMD crystal oscillator (PXO) and SMD voltage controlled/temperature complementary crystal oscillator (VCXO/TCXO/VCTCXO), which are mainly used in mobile phones, laptops, PHS, GPS devices and other wireless communication devices.SMD crystal oscillators for mobile phones are mainly characterized by high precision, high stability and small size, with the accuracy up to 5ppm. Meanwhile, the chip used is white in color, low in corrosion and not easy to vibrate, with stable quality. The size specifications are 7 5mm, 6 3.5mm, 5 3.2mm and 4 2.5mm.

The high precision and high stability quartz crystal oscillator in the fields of frequency standard, communication, electronic instrument, test device and precision measurement can be divided into TCXO, OCXO, VCXO, SPXO, LPXO (low noise crystal oscillator) and other types according to the long-term frequency stability.