How to get oscillation in a LC oscillator

[spswaroopa]

Hii
I hope all are doing well. I am facing a problem and I need all of you help.
I am designing a LC Oscillator with the architecture shown below, and I have taken LC values to achieve corresponding 1GHz frequency ( c=25pF, L=1nH, R=10k ohm) by using f=1/(2*pi*sqrt(L*C)). for a single stage, (if i take it as LC amplifier) I am getting 23 dB maximum gain at 1GHz. but after connecting two stages back to back as shown in figure, I am not getting any oscillations, I also tried by giving initial node voltage as 0.5V.
Observation : the gain at node X is higher than the node Y

How to choose the R values? and what are the issues I need to take care?
Why I am not getting the oscillations?
please any one help me to get the oscillator output. or suggest me any other architecture.

 

[frankrose]

Hi.

To get oscillation run for long time the transient analysis, and use TRAP integration method instead of GEAR,GEAR2 or else.
For faster start-up you can help with addition of transient noise in Spectre (if you use Cadence), set initial condition for the L or C, or couple a voltage spike to M1 or M2 gate.
I cannot recommend you other architecture, I don't know this circuit either so I don't know what is the function of R1,Rp. I guess they are loss model of inductors. This figure seems is coming from Razavi's book, there should be explained everything you need.
I recommend you to check loop gain of the connected amplifiers, separately is not the best.

 

[BradtheRad]

A symmetric astable circuit like this usually requires some imbalance between right and left sides, in order to get oscillations going.

With real components we rarely get perfect symmetry (thus oscillations are more reliable).

However a simulation often stagnates at the start because components match.

Change one or more component values to see if it results in oscillating behavior.

 

[spswaroopa]

Thank you to those who are all replied to my question.
I got the oscillation. I gave 0.5V voltage as initial condition set voltage to create imbalance then I get the wave forms.