1. Crystal: the collective called of quartz crystal resonators and quartz crystal oscillator. However, in consume electronics products, it often means resonator, and the latter we often call CXO.
First, talking about the resonator.
Resonators are generally classified as plug-ins (Dip) and Patch (SMD). Plug-in is divided into HC-49U, HC-49U / S, the tuning fork type (column). HC-49U commonly known as 49 U, some procurement commonly known as "high type", and HC-49U / S( 49 S )commonly known as the "dwarf type." In accordance with the volume, Fork resonator can be divided into 3 * 8, 2 * 6,1 * 5,
1 * 4 and so on. SMD series asst by size and pin. For example, 7 * 5 (0705), 6 * 3.5 (0603), 5 * 3.2 (5032). There are 4Pin and 2pin style.
The oscillator also can be divided into DIP and SMD. DIP can be divided by size and pin. For example, the full-size, often known as the rectangular of DIP-14, and square of DIP-8, known as the half- size. However, we should pay attention that here the DIP-14 and DIP-8 that is the internal oscillator core IC pins, the oscillator itself is 4 pin. By different kinds of applications to points, it can be divided into OSC (general oscillator), TCXO (temperature compensation), the VCXO (voltage-controlled), OCXO (thermostats) and so on.
3. Basic terminology. This may often confuse many purchasers.
Here we elect some common used resonator terminology to explain.
Frequency Tolerance (adjusted frequency difference): under the conditions set forth in the reference temperature (25 ± 2 ℃) with a nominal frequency of permitted deviation. General use PPM (parts per million) as unit.
Frequency Stability (temperature frequency difference): refers to the required temperature range, and allowed the nominal frequency deviation.
The unit is PPM
Aging (aging rate): under the conditions set forth in the crystal frequency over time to allow the relative changes. In years when measured in units of time called the aging rate.
Shunt Capacitance (electrostatic capacity): Equivalent circuit in tandem with the boom and the next capacitance, and also called capacitors, usually said C0.
Load Capacitance (load capacitance): together with the crystal resonant frequency FL decided to load the effective external capacitor, usually said CL.
Generally， the most concerned parameters are frequency tolerance and load capacitance. If the temperature range is wide, the temperature range will be requested.
4. How to choose.
Mainly talk about the resonator.
Theoretically speaking, as long as the parameters is determined,the election can be any type. For example, 49 and 49 U S replaced, 49 S and cylindrical patch replaced is no problem. However, in accordance with the actual selection, we think of the circuit characteristics, cost and convenience to considerations and options. Generally speaking, the simple application is mainly by cost considerations. But some products, or the equivalent circuit will be crystal resistance, power, etc. incentive request, will be in different models to choose. In addition, the patch was mainly in order to adapt to the increasing miniaturization of products and improve production efficiency. We heard some friends say, only choose 49U S can not be 49 or vice versa, this is a small misunderstanding.
Choosing oscillator is mainly depended on the requirements of circuit, in general , oscillator’s precision applications and the need to meet the requirements will be better. For instance, mobile phones, communication equipment stations, satellite, and so on.