no oscillation in oscillator

[chiu]

i designed a current mode OTA relaxation oscillator. the left part is OTA and the right part is schmitt trigger.
but i cannot get the oscillation in SPICE. i meant to give a 1 step voltage pulse kick start at feed back. but still cannot get the oscillation.
here is the schematic and plot of the circuit

 

[albbg]

I cannot see the image very well, it's too small. However it seems you used a battery to supply the circuits. You should use, instead, a pulse generator that starts at t=0 and then generates the Vcc for a time longer than your simulation time. However the voltage kick at the feedback should have the same effect.

 

[keith1200rs]

Ditto with the diagram - I cannot read it.

You could try kicking it down to zero.

One problem with getting oscillators to start in simulations can be the time step is too large. Make sure you set the maximum time step smaller than the period of oscillator by maybe a factor of 10. So, if you are expecting an oscillation at 1MHz, set a maximum time step of 100ns.

Keith.

Also, I cannot tell what Vref is connected to. You could try probing a few points in the circuit to see what happened immediately after the pulse.