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a question about the crysral oscillator used in RTC

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didibabawu

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A 32.768k crystal oscillator used in RTC(real time clock), I use the circuit in the picture. I want to know whether I need to add more inverters as buffer in the RTC system. I'm now using the same inv in the circuit. Both big L(6u) and small w(1u for nmos and 3u for pmos). Is there anything wrong in my circuits?

thank you very much.
 

Hi, schematic is correct. Buffer size depends upon loading but your numbers looks normal.
Please check suggested capacitance value with vendor and notce that R value are generally > 10Mohm.

Have fun.
 

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    didibabawu

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You also need the simulation of negative impedance seen from Xtal.

You need to have enough negative impedance to make sure it can oscillate.

By the may, low frequency XTAL oscillator may suffer from noise coupling.
 

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