RC and Crystal Oscillator

[amitk3553]

Hello all,

What is the difference in RC and crystal oscillator from implementation point of view for clocking purpose in SOCs.

like RC is used for low frequencies, but i had seen that it can be used for generating 20-30MHZ clocks, then whats the need of crystal oscillator???

I think because of more stable clocking by crystal oscillator?? We cannot produce low frequency clocks using crystal oscillators??

Please explain!!



Regards
Cam

 

[jpsganesh]

I think because of more stable clocking by crystal oscillator??

yes, u r right. X-tal OSC more stable than RC OSC

We cannot produce low frequency clocks using crystal oscillators??

low freq menas what? 32KHz also possible and may be less also.

RC OSC is cheaper than X-tal and simple too.

due to Temp and Humidity variation freq of RC OSC may varry. (more sensitive with temp and humidity)

"the difference in lead frame capacitance between package types will also affect the oscillation frequency, especially for low CEXT values"

tolerance of R and C valuse is very important.

pls find the attachment from PIC16F877A uC datasheet page no. 145 and 146

 

[Ow@i$]

at high frequency, Stability is the crucial thing and at higher frequency resistor exhibits properties of Cap and inductor and same goes for L an C .. thus unstable oscillator,
crystal osc perform much better and are more stable!!!