Passive crystals is the combination of quartz crystal resonator and quartz crystal oscillator, also known as quartz crystal resonator, the passive crystals have their own shortcomings, is the signal quality is bad, need to match some accurate peripheral circuit, such ability can play a role of their own, no crystals selection is mainly introduced how to select a good passive crystal vibration model, the following will introduce passive crystals selection of related content.
The first, pay attention to the frequency stability and phase noise
Passive crystals in the selection, the first to notice the stability of the passive crystals, only good stability can be used effectively, attention should be paid to the output of the oscillator frequency is affected by temperature changes, only affected by temperature changes little, passive crystals is excellent. Second is noticed its phase noise, phase noise is to display a parameters of the oscillator frequency spectrum purity, these two aspects should be focused on notice.
Second, pay attention to the output signal, frequency reproducibility
Passive quartz crystal resonator in the crystals selection manual according to its structure can be divided into different HC - 49 u, HC - 49 u/S, HC - 49 u/S, SMD, UM, UM - 1-5 and columnar crystals. Widely used in card reader. Digital cameras, computers, laptops, routers, switches, monitoring, security, etc. Also want to choose good, strong frequency reproducibility of output signal types, the output signal including falling edge along, over, load capacity, output voltage, output impedance and so on, are now common output signal of the square wave, sine wave, and chopped sine wave these kinds of waves. Frequency reproducibility is in a certain temperature, the oscillator is turned off before you wait for a moment, under the same temperature, and then boot, see if the difference between the output frequency and power off before frequency stability, can be judged by frequency reproducibility is good.
Third, pay attention to the aging rate, boot features, etc
Passive crystals in the selection, also should pay attention to each type of boot, aging rate and voltage-controlled characteristics, aging rate refers to, over time, such as a year, ten years, twenty years... crystal oscillator with the passage of time relative to the nominal frequency deviation value. Boot features is passive crystals after connected to the switch, use curve to represent the characteristics of frequency - time. Voltage-controlled characteristics is relative to the characteristics of mechanical adjusting range, the three also is in the selection of time needed to pay attention to, not the effect on it.
Passive crystals selection, that is, only before the selection of these are good to know, this will only be at the time of selection, has emphatically to pick out, not so hectic, after do all this well, all know, passive crystals will choose your satisfied, can use it better, at the time of selection to give it a try.
