Ring oscillator doesn't work - need explanation

[abcyin]

ring oscillator excitation

Hi, all

I am freshman about ring oscillator, I am trying to make a ring oscillator oscillate, but it doesn't work, the schematic is shown in the following fig., anybody can tell me the probable reason, and is the testbench right?

 

[Kaiserh]

Re: about ring oscillator

Hi abcyin,

As I can see from the pic, there is a excitation missing from the schematic. you can try to add one vpulse from cadence analogLib and use 10ns (depends on your Fosc) to excite the circuit. Connect the vpulse to your oscillator loop.

Hope it will help.

Best Regards
K

 

[calculus_cuthbert]

Re: about ring oscillator

you can also try and decrease the transient step time.. what is the frequency you are designing for.. according to that try to decrease the time step.. you can do that by going to analysis->transient-> options ->time step..

Try making the max step to be 10ps or just try to decrease it by an order of magnitude of the existing one