need help in ring vco design

[sekharcvr]

hi
iam designing vco in 180nm technology using differential ring oscillator.we have to get sinusoidal output.but we getting costant dc line.our circuit n testbench n output we r getting are attatched below. we r not getting any oscillations.

can any one help me if there are any mistakes in our ciruit. or give 3 stage differential ring oscillator circuit
thank u in advance.

 

[design_oriented]

Hi,
I am trying to design the same. Attached is a document that shows a differential ring oscillator.

Did you get a simple single ended three stage oscillator running?

Try that first to see if you can get it to oscillate.

It is a simple circuit with three inverters in series and the output of the last inverter connected to the gate of the first.

Make sure you set an initial condition and set an initial voltage with the Nodeset command in Spectre. This is needed to start the oscillations.