# Phase Noise Simulation of Ring Osc. with spectreRF

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#### Ruritania

##### Member level 5
phasenoise simulation

Hi, all,

How to get the right phase noise curve in spectreRF?? I got the positive one for the close-in, thought it must be wrong.

Ruri

#### khouly

spectrerf oscillator application notes

check the cadence application note about oscillator simulation , there is a steps to measure the phase noise

khouly

#### Ruritania

##### Member level 5

Thank you, Khouly, did you mean the following document?

There's nothing about the Ring oscillator phase noise simulation. My current issue on the phase noise simulation is that the "close-in" phase noise of the osc is positive, how can this be possible??

Thanks,
Ruri

#### khouly

why positive phase noise?

i think that's y the PSS detected the oscillation frequqncy with soome error , so the oscillation occur in frequancy shift

i am not an expert in PSS setup , but try to make it detect the oscillation frequency more accurately

another thing try to increase the time , tstab , which may increase the accuracy of the simulation

which this help u

Khouly

#### Grig

##### Full Member level 4
why phase noise is positive?

Hello
PASE NOISE can be positive. For ex modulate vco with noise source the phase noise spectrum will be ~1/f.
voltage noise (in dbc) can be positive in <1Hz bounds. In such case integral of dbc can be 1 (0db)
Spectre PSS (and not only spectre PSS) prediction of oscillator voltage noise near carrier is not true. It is analysis property.

Regards

#### buckaroo

##### Member level 3
positive phase noise

of course no!
Grig said:
Hello
PASE NOISE can be positive. For ex modulate vco with noise source the phase noise spectrum will be ~1/f.
voltage noise (in dbc) can be positive in <1Hz bounds. In such case integral of dbc can be 1 (0db)
Spectre PSS (and not only spectre PSS) prediction of oscillator voltage noise near carrier is not true. It is analysis property.

Regards

#### Grig

##### Full Member level 4
phase noise spectre

Hi