What is a crystal oscillator?

What is a crystal oscillator? What is its function? The topic of this article is a crystal oscillator. Some people say that this is a component. Others say that a quartz crystal oscillator uses the piezoelectric effect of quartz crystal (silicon dioxide crystal). It is a resonant device made. Let’s take a closer look at what a crystal oscillator is and what exactly is a crystal oscillator?

Quartz crystal oscillator is a high-precision and high-stability oscillator. It is widely used in various oscillation circuits such as color TVs, computers, remote controls, etc., as well as in communication systems for frequency generators and clock signals for data processing equipment. Provides a baseline signal for a specific system.

A quartz crystal oscillator is a resonant device made by utilizing the piezoelectric effect of quartz crystal (silicon dioxide crystal). Its basic composition is roughly as follows: cut a thin slice (referred to as a wafer for short) from a quartz crystal at a certain azimuth angle. It can be square, rectangular or circular, etc.), apply silver layers on its two corresponding surfaces as electrodes, solder a lead on each electrode to the pin, and add the packaging shell to form Quartz crystal resonator, referred to as quartz crystal or crystal, crystal oscillator. Its products are generally packaged in metal shells, but also in glass shells, ceramics or plastics.

If an electric field is applied to the two electrodes of a quartz crystal, the wafer will undergo mechanical deformation. On the contrary, if mechanical pressure is applied to both sides of the wafer, an electric field will be generated in the corresponding direction of the wafer. This physical phenomenon is called the piezoelectric effect. If an alternating voltage is applied to the two poles of the wafer, the wafer will generate mechanical vibration, and at the same time, the mechanical vibration of the wafer will generate an alternating electric field. Under normal circumstances, the amplitude of the mechanical vibration of the wafer and the amplitude of the alternating electric field are very small, but when the frequency of the external alternating voltage reaches a certain value, the amplitude increases significantly, which is much larger than the amplitude at other frequencies. This is This phenomenon is called piezoelectric resonance, which is very similar to the resonance phenomenon of the LC circuit. Its resonant frequency is related to the cutting method, geometry, size, etc. of the wafer.

What are the common types of crystal oscillators?

Many people don’t know much about the crystal oscillator. The crystal oscillator is known as the heart of the circuit. It cooperates with other components to generate pulse signals and issue instructions to achieve work. Crystal oscillators are widely used in different fields such as automotive electronics, smart home, digital electronics, security equipment, and communication equipment. There are many types of crystal oscillators. According to different performances, they can be divided into active crystal oscillators and passive crystal oscillators, active crystal oscillators, temperature-compensated crystal oscillators, voltage-controlled crystal oscillators, and voltage-controlled temperature-compensated crystal oscillators. Passive crystal oscillators are divided into two materials: quartz crystal oscillators and ceramic crystal oscillators.

According to the different equipment needs in different fields, many manufacturers choose to use crystal oscillators imported from Taiwan and crystal oscillator brands imported from Japan. Taiwanese crystal oscillator brands: Asia Ceramics crystal oscillator, Hongxing crystal oscillator, TXC crystal oscillator, heightened crystal oscillator, etc. Japanese crystal oscillator brands: KDS large vacuum crystal oscillator, Seiko Epson crystal oscillator, Citizen crystal oscillator, Kyocera crystal oscillator, NDK crystal oscillator, etc. Quartz crystal oscillators are divided into two types: patch and plug-in. The most common plug-in quartz crystals are cylindrical crystals and oval crystals. There are many package sizes of SMD crystal oscillators, mainly 7.0x5.0mm, 5.0x3.2mm, 3.2x2.5mm, 2.0x1.6mm, 1.6x1.2mm. Different package sizes of SMD crystal oscillators have different performance when used in different fields. different.

The most critical parameters for choosing a crystal oscillator are six points: the package size of the crystal oscillator, the frequency of the crystal oscillator (some frequencies are less commonly used), the accuracy deviation of the crystal oscillator, the load capacitance of the crystal oscillator, the temperature range requirements of the crystal oscillator, and the requirements of the active crystal oscillator. Supply voltage requirements. Different parameters are selected according to the products used by customers in different environments.

What are the classifications according to the various characteristics of crystal oscillators? According to the production materials: they can be divided into quartz crystal oscillators and ceramic crystal oscillators. Classification according to application characteristics: it can be divided into series resonance crystal oscillator and parallel resonance crystal oscillator. Classification according to load capacitance characteristics: it can be divided into low load capacitance type crystal oscillator and high load capacitance type crystal oscillator. According to the function and implementation technology of the crystal oscillator: the crystal oscillator can be divided into temperature compensated crystal oscillator (TCXO), voltage controlled crystal oscillator (VCXO), ordinary crystal oscillator (SPXO), and constant temperature crystal oscillator (OCXO).

Classified by packaging form: It can be divided into glass vacuum sealed crystal oscillator, metal shell packaged crystal oscillator, ceramic packaged crystal oscillator and plastic packaged crystal oscillator. Classification by appearance: It can be divided into rectangular crystal oscillator, cylindrical crystal oscillator and oval crystal oscillator. Classification according to resonant frequency accuracy: it can be divided into high-precision crystal oscillator, medium-precision crystal oscillator and ordinary crystal oscillator.

Classification of crystal oscillators

According to the different functions and implementation technologies of crystal oscillators, crystal oscillators can be divided into the following four categories:

1) Constant temperature crystal oscillator (hereinafter referred to as OCXO)

The solution for temperature stability of this type of crystal oscillator adopts constant temperature bath technology. The crystal is placed in a constant temperature bath. By setting a constant temperature working point, the bath body maintains a constant temperature state and is not affected by the external temperature within a certain range to achieve stable output. frequency effect. This type of crystal oscillator is mainly used in various types of communication equipment, including switches, SDH transmission equipment, mobile communication repeaters, GPS receivers, radio stations, digital TVs and military equipment. According to user needs, this type of crystal oscillator can have voltage control pins. The working principle of OCXO is shown in Figure 3 below:

The main advantage of OCXO is that due to the use of constant temperature bath technology, the frequency and temperature characteristics are the best among all types of crystal oscillators. Due to the precise circuit design, its short-term stability and phase noise are better. The main disadvantages are high power consumption, large size, and it takes about 5 minutes of heating time to work properly.

2) Temperature compensated crystal oscillator (hereinafter referred to as TCXO)

Its temperature stability solution uses some temperature compensation methods. The main principle is to sense the ambient temperature, appropriately transform the temperature information and then control the output frequency of the crystal oscillator to achieve the effect of stabilizing the output frequency. Traditional TCXO uses analog devices for compensation. With the development of compensation technology, many digitally compensated TCXOs have begun to appear. This digitally compensated TCXO is also called DTCXO. When using a microcontroller for compensation, we call it MCXO. Due to the use of digital Technology, this type of crystal oscillator has achieved high accuracy in temperature characteristics and can adapt to a wider operating temperature range. It is mainly used in the military industry and in harsh environments. With the joint efforts of the vast number of R&D personnel, our company has independently developed high-precision MCXO. Its design principles and design are world-leading. Equipped with a highly automated production and testing system, its monthly output can reach 5,000 pieces. The design principle is shown in Figure 4.

3) Ordinary crystal oscillator (SPXO)

This is a simple crystal oscillator, usually called a clock oscillator. Its working principle is as shown in Figure 3 except for the "voltage control", "temperature compensation" and "AGC" parts. It is completely completed by the free oscillation of the crystal. This type of crystal oscillator is mainly used in situations where stability requirements are not high.

4) Voltage controlled crystal oscillator (VCXO)

This is classified according to whether the crystal oscillator has a voltage control function. A type of crystal oscillator with a voltage control input pin is called a VCXO. The above three types of crystal oscillators can all have a voltage control port. The above is some analysis of the crystal oscillator, I hope it can help you.