I wonder about crystal oscillator designs.

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YUJIN

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Hi
I want to design crystal oscillator (pierce) but i have in trouble...
Proposed oscillation frequency is around 39MHz
And i used crystal
L~4mH C~4.1fF R~10ohm Co~2pF

C1 C2=20pF(shunt cap for drain to gnd& gate to gnd)

Feedback resistor ~ 1Mohm
Vdd~1.5V
Transistor gm~80u

However, my oscillator input/output settles
to same voltage , not oscillate...

When i change crystal cap to 200fF by myself for just trying.. then it oscillates.

What is the problem? ..
Can crystal motional cap affect oscillation?
 

verify that you're using the proper caps per the manufacturers recommendation. You don't show your circuit, so it's difficult to give any more advice.
 



Hello I changed frequency for 32.768kHz (AB26T) and i designed like attached.
And i set initial inductor current as 10nA, but the oscillation decreased and not started up.

Also, third attached file is open loop gain, phase
but phase doesn't go to 0 degree ....

In the conclusion,
1. Why doesn't my design start oscillation?
2. Can inverter Length size affect to oscillation?
 

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