andy2000a said:1. use need 48M Xtal spice R-L-C model ..
2. use AC sim check invert + Xtal have 180 degree phase shift
and frequency = Xtal freq
3. check invert gain
but the inv+Xtal is close loop system,how to simulate openloop gain?
can you post your spice command config?
I don't understand what you said, could you modify my sim file to make it work? tks a lot!Jet_wu said:increase the openloop gain when 0 phase shift
set the initial current of L in crystal model to speed up the tran simulation.
thank you very much, i'll try.Nobody said:Here is my verified crystal model .
Adjust the init current to speed up the oscillation start-up time .
.subckt QZS12MHz 1 2
*
lqz 1 11 0.1H IC=1e-07
cs 11 12 1.75fF
rqz 12 2 40
cp 1 2 5pF
.ends
tks a lot, i'll try.Jet_wu said:you'd better change the timestep to 0.5n and reduce the rise time of vdd. There is no need to run so much time.
add ".opt accurate"
Jet_wu, tk u very much.Jet_wu said:you'd better change the timestep to 0.5n and reduce the rise time of vdd. There is no need to run so much time.
add ".opt accurate"
Nobody said:The xtal's Q is very high ( 10^4 ~ 10^5) .
The LRC envelop transition time constant is propotional to its Q(quality factor) . So it take very long time to achive the full swing . Due to its high Q , the equivalent impedance is quite high and that get very small feedback . The oscillation depend strongly on this small feedback voltage as well as correct phase. It's easy to lose oscillation once your simulator roundoff or other numerical accuracy's problem . This sounds like communication or ADC's S/N ratio. The signal part dominate from IC setting . The noise come from the computer/simulator accuracy. The oscillation condition will be lost with lower S/N ratio .
My problem was the circuit didn't work, add ic value just speed up the oscillate time.ysz said:thank you very much, i'll try.Nobody said:Here is my verified crystal model .
Adjust the init current to speed up the oscillation start-up time .
.subckt QZS12MHz 1 2
*
lqz 1 11 0.1H IC=1e-07
cs 11 12 1.75fF
rqz 12 2 40
cp 1 2 5pF
.ends
but do you mean if there has enough sim time, the ic value is not need?
Humungus said:There are some books on crystal oscillators in the e-book forum
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