why xtal oscillator startup sim need ic current in inductor?

[John Xu]

xtal spice model

Hi,
I have a question on the startup simulation of xtal oscillator. We know, in normal, to kick off the simulation of xtal oscillator, we always add a initial current in the inductor of xtal's spice model, if not, it won't startup. Can anyone tell me why?

Same questions is for the RC oscillator, we alway set an initial condition to startup it.

From the view of sloving the differtial equations, would you pls. tell me why?

Thanks in advance

 

[huojinsi]

xtal spice

Hi,
I have a question on the startup simulation of xtal oscillator. We know, in normal, to kick off the simulation of xtal oscillator, we always add a initial current in the inductor of xtal's spice model, if not, it won't startup. Can anyone tell me why?

If a initial current isn't added, the circuit can work, only the startup time is very long! not as u say the circuit won't startup!

 

[rfsystem]

initial current of inductor

Any initial condition change the DC condition because the .OP is done before transient. Most designers avoid that by using a start pulse which is zero at time zero. A more realistic startup is using a noise source made of a PWL with amplitude similar to the real noise.

 

[John Xu]

xtal spice models

If a initial current isn't added, the circuit can work, only the startup time is very long! not as u say the circuit won't startup![/quote]

If you simulate a RC oscillator and you did not add initial condition, you will never start it up. why?

Added after 7 minutes:

Adding initial condition is to emulate the noise source, e.g., set initial condition voltage/current, powerup supply etc.., because, we know, there is no noise model for transient analysis. so we need add some disturbing signal to osc to made it bigger and bigger with positavie feedback. What I just want to know , from the view of sloving the differtial equations, how it works.

Thanks