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

[holddreams]

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.

 

[sunking]

crystal oscillator dutycycle

add a initial condition and try

 

[holddreams]

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?

 

[sunking]

20mhz oscillator circuit

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

 

[holddreams]

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.

 

[crystalguy]

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.

 

[mitgrace]

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

 

[holddreams]

20mhz crystal oscillator circuit

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

 

[adscrz]

crystal oscillator,duty cycle

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

May be can help u.

 

[micheal_han]

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