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How to design a 20MHz crystal oscillator with 50% duty cycle

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holddreams

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crystal oscillator circuit 20mhz

How to design a 20MHz crystal oscillator circuit with 50% duty cycle?

I use 0.5um CMOS Logic process,and choose the circuit like some papers said,
but the duty cycle of post-simulation result is not exactly 50%.

I add decoupling capacitor between VDD and VSS.

How can I control the duty cycle to 50%?
How long should I simulate the circuit?10u?20u?or else?
Once I simulate the circuit for 1.5ms,and the duty cycel change with time.....

Thanks.
 

crystal oscillator dutycycle

add a initial condition and try
 

crystal with duty cycles changed

I give the conductor an initial current ,and run the simulation,
but the duty cycle change with time.
Is the initial condition wrong?
 

20mhz oscillator circuit

does the output peak to peak is stable? what kind osc? what kind crystal oscillator?
 

crystal oscillator 50% duty cycle

a pierce circuit.
when simulate a lont ime, the duty cycle is :
tt_corner: 49%
ss_corner:46.8%
ff_corner:52.8%

How can I get 50% duty cycle?
The three corners can not get 50% duty cycle at the same time.
 

20mhz crystal oscillator ic

The answer to your question is that you cannot achieve a true 50% duty cycle unless you have infinite bandwidth. Due to the charge storage elements in the inverter (I am assuming a pierce oscillator using a CMOS inverter) the symmetry will be skewed.
 

20mhz crystal circuits

it is hard to control 50 -50 duty for different corner . you can serires a resister to
output circuit , adjust resister , you can get more gain , that you can gte better 50-50 in the corner process

Added after 2 minutes:

the simulation time , i add initial condition , and simulation about 200us for ss/tt/ff , high/low voltage , -40 , 125 . becasue some corner don't need 200us , but in the worst case , maybe 200us is need for simulation time
 

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    holddreams

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20mhz crystal oscillator circuit

hi,mitgrace,
can you share me with the 20MHz crystal simulation model?
thanks.
 

crystal oscillator,duty cycle

Search : A 1.2-um CMOS Current-Controlled Oscillator.pdf
in google

May be can help u.
 

hi holddreams,
Can you upload the circuits you designed? And I help you analysis.
 

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