Why do we use schmitt trigger as xstal oscillator buffer?

[OMEsystem]

schmitt trigger oscillator

We can see some application material of xstal oscillator that they use
a schmitt trigger to follow the oscillator. What's the reason behind it?
For better noise? better interference immunity?

 

[davidgrm]

oscillator buffer

a crystal will most likely create a sine wave. This is an analogue signal and does not have a nice square digital waveform. The schmitt will convert the wave to a good digital signal. A non schmitt trigger device would generate false signals as the waveform crosses beteween the 0 to 1 region

 

[subharpe]

shmitt trigger

In addition to what davidgrm said, pulse shaping is another reason why it is done.

 

[Fom]

osilator buffer

Because starp-up time of crystal oscilator may be very large (seconds). At the beginning the oscillation amplitude is very low and gradually increases from uV to Vcc. So at the beginning any noise can interfere with oscillated frequency and cause glitches. Shmitt trigger guarantees that output is toggling when oscillator amplitude is more than Shmitt trigger hysteresis and large enough to be insensetive to noise.

 

[manish12]

oscilator buffer

in addition , we can use the driving ability of Schmitt trigger rather than oscillator directly ,

Schmitt trigger act as filter of noise / etc in both direction i.e +ve and -ve phase , as well wave shaping ckt ,it can also use to convert logic to desired logic level , etc

 

[OMEsystem]

oscillator schmitt trigger

in addition , we can use the driving ability of Schmitt trigger rather than oscillator directly ,

Schmitt trigger act as filter of noise / etc in both direction i.e +ve and -ve phase , as well wave shaping ckt ,it can also use to convert logic to desired logic level , etc

How come Schmitt trigger act as noise filter? Because of the hysteresis?Or..?
Would you explain it in more detail?

Thank you,

Added after 5 minutes:

In addition to what davidgrm said, pulse shaping is another reason why it is done.

Does pulse shaping mean correcting the duty cycle to 50-50?

 

[jecyhale]

clock oscillator driving schmitt trigger.

We can see some application material of xstal oscillator that they use
a schmitt trigger to follow the oscillator. What's the reason behind it?
For better noise? better interference immunity?

I use the self-biased inverter as the buffer, but I use the clock after some time by counte the clock.