Crystal oscillators are also called active crystal oscillators. The other type is called crystal resonators (passive crystal oscillators). Both are generally referred to as crystal oscillators. In the purchase of crystal oscillators, there are some differences between the purchase requirements of active and passive crystal oscillators. Today, I will talk about the purchase precautions of the 5-point crystal oscillator provided.
　　1. The working principle of crystal oscillator
　　The crystal oscillator can generate the clock frequency signal necessary for the central processing unit (CPU) to execute instructions. All instructions of the CPU are executed on this basis. The higher the frequency of the clock signal, the faster the CPU generally runs. As long as it is an electronic product that contains a CPU, it contains at least one clock source. Even if the actual oscillator circuit is not visible outside, it is integrated inside the chip. It is called the heart of the circuit system.
　　Second, the purchase requirements of crystal oscillators
　　1. Appearance inspection
　　By checking the appearance of the product, whether the marking text is clear and standard, whether there are cracks on the surface of the appearance, and whether the pins have been soldered. If the product is found to be imperfect on the outside, it should not be used.
　　2. Frequency
　　The customer chooses the appropriate frequency according to the product requirements. The frequency is the most important, and the frequency cannot be replaced casually. Negotiations must be conducted after passing the qualification verification or professional test. If the frequency required by the actual circuit is 13.56MHZ, don't use it with a similar frequency if there is no supply.
　　3. Model
　　When using a crystal oscillator, you must see the model mark of the shell. The model indicates a number of parameters of the crystal oscillator. According to the customer's product requirements, we can find out our model by corresponding to the product parameters. Then send the detailed parameter specification to the customer for confirmation before it can be shipped normally. If the crystal oscillator model is not selected properly, it will cause application errors.
　　4. Output mode
　　When choosing a crystal oscillator, consider the output type of the crystal oscillator required by the circuit, generally divided into level output and differential output, level output methods are: CMOS, TTL, HCMOS; and CMOS is the most commonly used output type , And differential output methods are: LVPECL, LVDS, HCSL, CML; and LVPECL, LVDS commonly used differential output types. There is no need to change between different output types, especially differential and ordinary crystal oscillators.
　　5. Substitution principle
　　If a crystal oscillator is damaged, in principle, it should be replaced by the original model crystal oscillator. When the original model is not available, it is best to consider replacing it with another model or other type of crystal oscillator after testing.