There are source crystal:
There is an internal oscillator of the DSP without DSP. The signal quality is good, relatively stable, and the connection method is relatively simple (mainly for power filtering, usually a PI filter network composed of a capacitor and inductance. The resistance filtering signal of the value is only available), and no complex configuration circuit is required.
There is a definition of source crystals, which means that the usual method is usually connected: one foot is suspended, two feet are ground, three feet are connected to the output, and the four feet are connected to the voltage. Compared to the passive crystals, the defect of the source crystal is that its signal level is fixed. It is necessary to choose the appropriate output level, poor flexibility, and high price.
For sensitive applications required by timing, I personally think that the active crystal is good, because it can be selected from more precise crystals, or even high -end temperature compensation crystals. Some DSPs have no vibration circuit inside, and can only use active crystals, such as TI's 6000 series. Source crystals are usually large than passive crystals, but now many source crystals are table stickers, the volume is equivalent to the crystal, and some are even smaller than many crystals.
Patriotic crystal:
The passive crystal requires the oscillator in the DSP tablet. The passive crystal has no voltage problem. The signal level is variable, that is, it is determined by the vibration circuit. The same crystal can be applied to a variety of voltage, which can be used for DSP requirements required by a variety of different clock signal voltage, and the price is usually low. Therefore, it is recommended to use crystals for general applications. Producer.
The passive crystal is compared to the crystal. Its shortcomings are poor signal quality. Generally, accurate matching peripheral circuits (capacitors, inductors, resistors, etc. for signal matching) need to be used. Essence It is recommended to use high -accurate quartz crystals, so as not to use as low accuracy as much as possible.
The difference between source crystals and passive crystals is that the source of the source crystal has no load, and the passive crystal has a load without voltage.
A few points of precautions for crystal vibration:
1. The CPU that needs to be multiplied needs to be configured with the PLL peripheral configuration circuit, which is mainly isolation and filtering;
2. The crystal crystal below 20MHz is basically the device of the base frequency. The stability is good. Most of the 20MHz or more are harmonic (such as 3 harmonics, 5 harmonics, etc.). Using low -frequency devices, after all, the peripheral configuration required for PLL circuits for frequent frequency is mainly capacitors, resistors, and inductors.
3. The length of the clock signal wiring is as short as possible, the width of the line is as large as possible, and the distance between the other printing line is as large as possible.
4. There are special design requirements when introducing the clock signal through the backboard, and you need to refer to the relevant information in detail.
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