# How to use transient analysis report for PSS analysis in Spectre?

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#### Ding Yan

##### Newbie level 4
Hi guys,

When I was trying to evaluate the Phase Noise performance of my LC tank VCO, I got a problem with the tools. I was following the Spectre RF tutorial from Cadence. It mentioned:

"Note: If your oscillator circuit does not contain a stimulate to start the oscillator, you must run a transient analysis before you run this PSS analysis. From the transient analysis, you save the node voltages and use them as initial conditions to start the oscillator in the PSS analysis"

May I ask, how can I "...save the node voltages and use them as initial conditions to start the oscillator in the PSS analysis." ?

I used a Isource between the V+ and V- to provide a initial current pulse to start the oscillation.I tried to run PSS and Pnoise in two ways.

The first one: After running transient analysis. I removed the Isource and set up the environments for PSS and Pnoise. Then I got this ERROR:

"Error found by spectre at time = 1 ns during periodic steady state analysis
pss'.
V(V+) is too small to reliably detect the period of the oscillator. This
may be because nodes with insignificant signal levels were chosen, or
it may be because the oscillator was never properly started."

The second way is I do not remove the Isource and set up PSS and Pnoise and run simulation directly. Then I got:

"Error found by spectre during periodic steady state analysis pss'.
I0' is a periodic input signal, which is inconsistent with autonomous
circuits.

Analysis pss' terminated prematurely due to error.

Error found by spectre.
PSS analysis must be executed before pnoise. Analysis skipped."

Can anybody give me some instruction on this? Thank you.

Yan

#### BigBoss

cadence pss is too small to reliably detect

In "option" window of transient analysis, there is a field to fill that you can save the transient analysis results by defining a file name as for instance "transient.ts"..
Then you can use this file in PSS analysis again in option window by filling simply the file name which you have save before..

#### Ding Yan

##### Newbie level 4
pnoise analysis setup

BigBoss said:
In "option" window of transient analysis, there is a field to fill that you can save the transient analysis results by defining a file name as for instance "transient.ts"..
Then you can use this file in PSS analysis again in option window by filling simply the file name which you have save before..

Thank you. I highlighted (saveinit) and the problem was resolved.

Yan

swjtuliwang

### swjtuliwang

Points: 2

#### swjtuliwang

##### Newbie level 1
In PSS analysis,there are a lot of fields in option window,which field did i filling in?
can you show it in detail,thank you.....

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