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The difference, application scope and usage of passive crystal and active crystal oscillator

Release date:2019-12-24


1. Passive crystal oscillator - the passive crystal oscillator needs to use the oscillator in the DSP chip, and the proposed connection method is shown in the data manual. Passive crystal without the problem of voltage, signal level is variable, and that is to say, according to the vibration of the circuit, the same crystal can be applied to all kinds of voltage, can be used in a variety of different clock signal voltage requirements of DSP, and the price is usually lower, so if conditions allow it is recommended to use crystal general applications, it is particularly suitable for product line rich mass producers.


The disadvantage of passive crystals is that the signal quality is poor compared to the crystal oscillator, so it is usually necessary to match the peripheral circuit (capacitance, inductance, resistance, etc., used for signal matching) accurately. When changing crystals at different frequencies, the peripheral configuration circuit needs to be adjusted accordingly. High precision quartz crystals are recommended and low precision ceramics are avoided as far as possible.


2, active crystal, crystal active vibration does not need DSP internal oscillator, signal quality is good, stable, and the connection method is relatively simple, mainly to complete the power filtering, usually using capacitive and inductive type PI filtering network, by the output resistance signal small resistance filter), do not need complex configuration circuit.


Common USES of active crystal oscillators: one foot suspended, two feet grounded, three feet connected to the output, four feet connected to the voltage. The disadvantage of an active crystal oscillator, compared with a passive crystal, is that its signal level is fixed, so it is necessary to select the appropriate output level, poor flexibility, and high price.


For applications with time-sensitive requirements, I think it is best to use an active crystal oscillator, as more precise crystal oscillators can be selected, and even advanced temperature compensated crystal oscillators can be selected. Some DSPS have no internal oscillator circuit and can only use active crystal oscillators, such as the 6000 series of TI. Active crystal oscillators are usually larger than passive crystals, but many active crystal oscillators are now on the surface and are the size of crystals or even smaller than many crystals.